जावा 8 में लैम्ब्डा भाव

लंबे समय से प्रतीक्षित लैम्ब्डा के भाव अंततः जावा 8 के नए संस्करण में दिखाई दिए। शायद नवीनतम संस्करण में यह सबसे महत्वपूर्ण नई विशेषता है; वे आपको तेजी से लिखने और कोड को स्पष्ट करने की अनुमति देते हैं, और कार्यात्मक प्रोग्रामिंग की दुनिया का दरवाजा भी खोलते हैं। इस लेख में मैं बताऊंगा कि यह कैसे काम करता है।



90 के दशक में जावा को एक वस्तु-उन्मुख भाषा के रूप में कल्पना की गई थी, जब अनुप्रयोग-विकास में ऑब्जेक्ट-ओरिएंटेड प्रोग्रामिंग मुख्य प्रतिमान था। इससे पहले, ऑब्जेक्ट-ओरिएंटेड प्रोग्रामिंग थी, लिस्प और स्कीम जैसी कार्यात्मक प्रोग्रामिंग भाषाएं थीं, लेकिन अकादमिक वातावरण के बाहर उनके फायदे की सराहना नहीं की गई थी। हाल ही में, कार्यात्मक प्रोग्रामिंग का महत्व काफी बढ़ गया है क्योंकि यह समवर्ती प्रोग्रामिंग और इवेंट-आधारित प्रोग्रामिंग ("प्रतिक्रियाशील") के लिए अच्छी तरह से अनुकूल है। इसका मतलब यह नहीं है कि ऑब्जेक्ट ओरिएंटेशन खराब है। इसके विपरीत, इसके बजाय, एक जीत की रणनीति ऑब्जेक्ट-ओरिएंटेड प्रोग्रामिंग और कार्यात्मक को मिलाना है। यह समझ में आता है भले ही आपको समानता की आवश्यकता न हो। उदाहरण के लिए, संग्रह पुस्तकालयों को एक शक्तिशाली एपीआई मिल सकता है यदि भाषा में कार्यात्मक अभिव्यक्तियों के लिए सुविधाजनक वाक्यविन्यास है।



जावा 8 में एक बड़ा सुधार इसके उद्देश्य उन्मुख आधार पर कार्यात्मक सॉफ्टवेयर निर्माण के लिए समर्थन का जोड़ है। इस लेख में, मैं मूल सिंटैक्स का प्रदर्शन करूंगा और इसे कई महत्वपूर्ण संदर्भों में कैसे उपयोग करूं। लंबोदर की अवधारणा के मुख्य बिंदु:

• एक लैम्ब्डा अभिव्यक्ति मापदंडों के साथ कोड का एक ब्लॉक है।
• जब आप समय में बाद में बिंदु पर कोड के एक ब्लॉक को निष्पादित करना चाहते हैं, तो एक लैम्ब्डा अभिव्यक्ति का उपयोग करें।
• लैम्ब्डा अभिव्यक्तियों को कार्यात्मक इंटरफेस में बदला जा सकता है।
• लैंबडा एक्सप्रेशंस के दायरे से अंतिम चर तक पहुंच है।
• मेथड और कंस्ट्रक्टर रेफरेंस मेथड्स या कंस्ट्रक्टर्स को बिना बुलाए रेफर करते हैं।
• अब आप डिफॉल्ट मेथड्स और स्टैटिक मेथड्स को स्पेसिफिक में जोड़ सकते हैं जो स्पेसिफिक इम्प्लीमेंटेशन प्रदान करते हैं।
• आपको कई इंटरफ़ेस से डिफ़ॉल्ट विधियों के बीच किसी भी टकराव को हल करना होगा।

लंबोदर की जरूरत क्यों है?

एक लंबोदर अभिव्यक्ति कोड का एक ब्लॉक है जिसे किसी अन्य स्थान पर पारित किया जा सकता है, इसलिए इसे बाद में, एक या अधिक बार निष्पादित किया जा सकता है। सिंटैक्स (और एक जिज्ञासु नाम) में जाने से पहले, आइए एक कदम पीछे देखें और देखें कि आपने जावा में कोड के समान ब्लॉक का उपयोग कहां किया था।



यदि आप अलग थ्रेड में क्रियाओं को निष्पादित करना चाहते हैं, तो आप उन्हें Runnable



की run



विधि में डालते हैं, जैसे:

 class MyRunner implements Runnable { public void run() { for (int i = 0; i < 1000; i++) doWork(); } ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     

फिर, जब आप इस कोड को निष्पादित करना चाहते हैं, तो आप MyRunner



वर्ग को MyRunner



। आप थ्रेड पूल में उदाहरण डाल सकते हैं, या इसे आसान कर सकते हैं और एक नया धागा शुरू कर सकते हैं:

 MyRunner r = new MyRunner(); new Thread(r).start();
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     

मुख्य बिंदु यह है कि run



विधि में कोड होता है जिसे अलग थ्रेड में निष्पादित करने की आवश्यकता होती है।



एक कस्टम तुलनित्र का उपयोग करके छंटाई पर विचार करें। यदि आप लाइनों को लंबाई के आधार पर क्रमबद्ध करना चाहते हैं, और डिफ़ॉल्ट रूप से नहीं, तो आप Comparator



विधि को sort



विधि से पास कर सकते हैं:

 class LengthStringComparator implements Comparator<String> { public int compare(String firstStr, String secondStr) { return Integer.compare(firstStr.length(),secondStr.length()); } } Arrays.sort(strings, new LengthStringComparator ());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     

sort



विधि अभी भी compare



पद्धति को कॉल करती है, तत्वों को फिर से व्यवस्थित करती है यदि वे क्रम में नहीं हैं, जब तक कि सरणी को सॉर्ट नहीं किया जाता है। आप तत्वों की तुलना करने के लिए आवश्यक कोड स्निपेट के साथ sort



विधि प्रदान करते हैं, और यह कोड बाकी प्रकार के लॉजिक में एम्बेडेड होता है, जिसे शायद आपको फिर से परिभाषित करने की आवश्यकता नहीं है। ध्यान दें कि Integer.compare (, )



कॉल करने पर शून्य वापस आ जाता है यदि x और y बराबर हैं, तो ऋणात्मक संख्या यदि x <y, और सकारात्मक संख्या है तो x> y। यह स्थिर विधि जावा 7 में जोड़ी गई थी। आपको x और y की तुलना करने के लिए x - y की गणना करने की आवश्यकता नहीं है, क्योंकि गणना विपरीत संकेत के बड़े ऑपरेंड के लिए अतिप्रवाह का कारण बन सकती है।



आस्थगित निष्पादन के एक अन्य उदाहरण के रूप में, एक बटन के लिए कॉलबैक पर विचार करें। आप कॉलबैक कार्रवाई को उस वर्ग की विधि में डालते हैं जो श्रोता इंटरफ़ेस को लागू करता है, एक उदाहरण बनाता है, और उदाहरण पंजीकृत करता है। यह एक ऐसा सामान्य परिदृश्य है कि कई प्रोग्रामर वाक्यविन्यास का उपयोग करते हैं "एक अनाम वर्ग का अज्ञात उदाहरण":

 button.setOnAction(new EventHandler<ActionEvent>() { public void handle(ActionEvent event) { System.out.println("The button has been clicked!"); } });
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     

handle



विधि के अंदर कोड यहाँ महत्वपूर्ण है। जब भी कोई बटन दबाया जाता है तो इस कोड को निष्पादित किया जाता है।



चूंकि Java 8 जावाएफएक्स को स्विंगिंग जीयूआई टूलकिट के उत्तराधिकारी के रूप में रखता है, इसलिए मैं इन उदाहरणों में जावाएफएक्स का उपयोग करता हूं। विवरण मायने नहीं रखता। प्रत्येक उपयोगकर्ता इंटरफ़ेस लाइब्रेरी में, चाहे स्विंग, जावाएफ़एक्स या एंड्रॉइड, आप बटन को कुछ कोड पास करते हैं जिसे आप बटन दबाए जाने पर चलाना चाहते हैं।



तीनों उदाहरणों में आपने एक ही दृष्टिकोण देखा। कोड का एक ब्लॉक किसी पर पारित किया गया था - एक थ्रेड पूल, छँटाई विधि, या बटन। इस कोड को कुछ समय बाद कहा गया था।



अब तक जावा में पासिंग कोड आसान नहीं रहा है। आप कहीं भी कोड ब्लॉक पास नहीं कर सकते। जावा एक ऑब्जेक्ट-ओरिएंटेड भाषा है, इसलिए आपको एक क्लास से संबंधित ऑब्जेक्ट बनाना होगा जिसमें सही कोड के साथ एक विधि हो।

अन्य भाषाओं में, आप सीधे कोड के ब्लॉक के साथ काम कर सकते हैं। जावा डिजाइनरों ने लंबे समय तक इस सुविधा को जोड़ने का विरोध किया है। आखिरकार, जावा की महान ताकत इसकी सादगी और निरंतरता में निहित है। यदि भाषा में वे सभी कार्य शामिल हैं जो थोड़े अधिक संक्षिप्त कोड देते हैं, तो भाषा बहुत गड़बड़ हो सकती है। हालाँकि, उन अन्य भाषाओं में, धारा प्रवाह या एक क्लिक बटन हैंडलर को पंजीकृत करना आसान नहीं है; उनके कई एपीआई सरल, अधिक सुसंगत और शक्तिशाली हैं। जावा में, एक समान इंटरफेस लिख सकता है जो क्लास ऑब्जेक्ट्स को स्वीकार करता है जो एक विशेष फ़ंक्शन को लागू करते हैं, लेकिन ऐसे एपीआई का उपयोग करने के लिए असुविधाजनक होगा।



हाल ही में, सवाल यह नहीं है कि कार्यात्मक प्रोग्रामिंग के लिए जावा का विस्तार करना है या नहीं, लेकिन यह कैसे करना है। यह स्पष्ट होने से पहले कि जावा के लिए यह अच्छी तरह से काम करता है, कई वर्षों के प्रयोग हुए। अगले भाग में, आप देखेंगे कि आप जावा 8 में कोड के ब्लॉक के साथ कैसे काम कर सकते हैं।

लैम्ब्डा एक्सप्रेशन सिंटैक्स

पिछले छँटाई उदाहरण पर फिर से विचार करें। हम एक कोड में पास होते हैं जो यह जांचता है कि कौन सी रेखा छोटी है। हम हिसाब लगाते हैं

 Integer.compare(firstStr.length(), secondStr.length())
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     

firstStr



और secondStr



क्या हैं? वे दोनों लाइनें हैं! जावा एक दृढ़ता से टाइप की गई भाषा है, और हमें प्रकार निर्दिष्ट करने होंगे:

 (String firstStr, String secondStr) -> Integer.compare(firstStr.length(),secondStr.length())
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     

आपने अभी-अभी अपना पहला लंबोदर एक्सप्रेशन देखा है! इस तरह की अभिव्यक्ति बस कोड का एक ब्लॉक है साथ ही किसी भी चर के विनिर्देश के साथ जिसे कोड को पारित किया जाना चाहिए।



ऐसा नाम क्यों? कई साल पहले, जब अभी तक कोई कंप्यूटर नहीं थे, तो तर्कशास्त्री अलोंजो चर्च औपचारिक रूप से गणना के लिए गणितीय फ़ंक्शन के लिए इसका क्या अर्थ है, यह औपचारिक रूप देना चाहता था। (उत्सुकता से, ऐसे कार्य हैं जो अस्तित्व के लिए जाने जाते हैं, लेकिन कोई भी अपने मूल्यों की गणना करना नहीं जानता है।) उन्होंने मापदंडों को चिह्नित करने के लिए ग्रीक अक्षर लैम्ब्डा (λ) का उपयोग किया। यदि वह जावा एपीआई के बारे में जानता है, तो वह कुछ ऐसा नहीं लिखेगा जो आपने देखा था, सबसे अधिक संभावना है।



पत्र λ क्यों है? क्या चर्च ने वर्णमाला के सभी अक्षरों का उपयोग किया था? वास्तव में, प्रिंसिपिया मैथेमेटिका के आदरणीय कार्य में प्रतीक का उपयोग ener मुक्त चर को दर्शाने के लिए किया गया है जिसने चर्च को मापदंडों के लिए राजधानी लैंबडा (Λ) का उपयोग करने के लिए प्रेरित किया। लेकिन अंत में, उन्होंने पत्र के निचले संस्करण में स्विच किया। तब से, चर मापदंडों के साथ एक अभिव्यक्ति को "लंबोदर अभिव्यक्ति" कहा जाता है।



आपने अभी जावा में लैम्बडा एक्सप्रेशन का एक रूप देखा है: पैरामीटर, एरो -> और एक्सप्रेशन। यदि कोड एक गणना करता है जो एक एकल अभिव्यक्ति में फिट नहीं होता है, तो इसे उसी तरह से लिखें जैसे आप एक विधि लिखेंगे: {} में संलग्न और स्पष्ट return



। उदाहरण के लिए

 (String firstStr, String secondStr) -> { if (firstStr.length() < secondStr.length()) return -1; else if (firstStr.length() > secondStr.length()) return 1; else return 0; }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     

यदि लैम्ब्डा अभिव्यक्ति में कोई पैरामीटर नहीं है, तो आप अभी भी खाली ब्रैकेट लगाते हैं, ठीक उसी तरह जैसे बिना मापदंडों के एक विधि के साथ:

 () -> { for (int i = 0; i < 1000; i++) doWork(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     

यदि लंबोदर अभिव्यक्ति के पैरामीटर प्रकार का अनुमान लगाया जा सकता है, तो आप उन्हें छोड़ सकते हैं। उदाहरण के लिए

 Comparator<String> comp = (firstStr, secondStr) // Same as (String firstStr, String secondStr) -> Integer.compare(firstStr.length(),secondStr.length());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     

यहां, संकलक निष्कर्ष निकाल सकता है कि firstStr



और secondStr



तार होना चाहिए, क्योंकि लैम्ब्डा अभिव्यक्ति स्ट्रिंग तुलनित्र को सौंपा गया है। (हम इस असाइनमेंट पर बाद में विचार करेंगे।)



यदि विधि के प्रकार का एक पैरामीटर प्रदर्शित किया जा रहा है, तो आप कोष्ठक को छोड़ भी सकते हैं:

 EventHandler<ActionEvent> listener = event -> System.out.println("The button has been clicked!"); // Instead of (event) -> or (ActionEvent event) ->
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     

आप लैम्बडा पैरामीटर में एनोटेशन या final



संशोधक को उसी तरह से जोड़ सकते हैं जैसे कि विधि पैरामीटर के लिए:

 (final String var) -> ... (@NonNull String var) -> ...
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     

आप लैंबडा एक्सप्रेशन के परिणाम प्रकार को कभी निर्दिष्ट नहीं करते हैं। यह हमेशा संदर्भ से स्पष्ट है। उदाहरण के लिए, अभिव्यक्ति

 (String firstStr, String secondStr) -> Integer.compare(firstStr.length(), secondStr.length())
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     

एक संदर्भ में प्रयोग किया जा सकता है जहां एक int



प्रकार के परिणाम की उम्मीद है।



ध्यान दें कि एक लैम्ब्डा अभिव्यक्ति कुछ शाखाओं में एक मूल्य नहीं लौटा सकता है, और दूसरों में वापस नहीं कर सकता है। उदाहरण के लिए, (int x) -> { if (x <= 1) return -1; }



(int x) -> { if (x <= 1) return -1; }



अमान्य है।

कार्यात्मक इंटरफेस

जैसा कि हमने चर्चा की, जावा में कई मौजूदा इंटरफेस हैं जो कोड के ब्लॉक को Runnable



, जैसे कि Runnable



या Comparator



। इन इंटरफेस के साथ लैम्ब्डा एक्सप्रेशन पिछड़े हुए हैं।



जब भी एक सार विधि के साथ एक इंटरफ़ेस ऑब्जेक्ट की उम्मीद की जाती है, तो आप एक लैम्ब्डा अभिव्यक्ति की आपूर्ति कर सकते हैं। इस तरह के एक इंटरफ़ेस को एक कार्यात्मक इंटरफ़ेस कहा जाता है।



आप आश्चर्यचकित हो सकते हैं कि एक कार्यात्मक इंटरफ़ेस में एक एकल सार पद्धति क्यों होनी चाहिए। इंटरफ़ेस सार में सभी तरीके नहीं हैं? वास्तव में, इंटरफ़ेस के लिए Object



क्लास के तरीकों को ओवरराइड करना हमेशा संभव था, जैसे कि toString



या clone



, और ये घोषणाएं तरीकों को सार नहीं बनाती हैं। (जावा एपीआई में कुछ इंटरफेस javadoc टिप्पणियों को संलग्न करने के लिए Object



विधियों को ओवरराइड करते हैं। एक उदाहरण के लिए तुलनित्र एपीआई देखें।) अधिक महत्वपूर्ण बात, जैसा कि आप जल्द ही देखेंगे जावा 8 में, इंटरफेस गैर-अमूर्त विधियों की घोषणा कर सकते हैं।



एक कार्यात्मक इंटरफ़ेस में रूपांतरण प्रदर्शित करने के लिए, Arrays.sort



विधि पर विचार करें। इसके दूसरे पैरामीटर में एक एकल विधि के साथ Comparator



इंटरफ़ेस की एक उदाहरण की आवश्यकता होती है। बस लंबोदर प्रदान करें:

 Arrays.sort(strs, (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length()));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     

पर्दे के पीछे, Arrays.sort



पद्धति को कुछ वर्ग की एक वस्तु मिलती है जो कि Comparator . compare -. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



, - , - Java. , , , (String, String) -> int



, , . Java - Object



, Object



. Java , .



Java API java.util.function. , BiFunction <T, U, R>



, U R. :

BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());





, . Arrays.sort



, BiFunction



. , . Java . , Comparator



, , . Java 8 . - - , , .



java.util.function Java 8 API , , , . , - , API, . , @FunctionalInterface



. . , . Javadoc , . . , , . @FunctionalInterface



- .



, , checked . - checked , . , :

Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





Runnable.run



, . , . -. , . , call



Callable



. , Callable ( return null



).





, , . , , event



, . ,

button.setOnAction(event -> System.out.println(event));





, println



setOnAction



. :

button.setOnAction(System.out::println);





System.out::println



, - x -> System.out.println(x)



.



, , . :

Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



-, . , System.out::println



x -> System.out.println(x)



. , Math::pow



(x, y) -> Math.pow(x, y)



. . , String::compareToIgnoreCase



- , (x, y) -> x.compareToIgnoreCase(y)



.



, . , Math.max



, int



double



. , , Math.max



. , -, . .



this



. , this::equals



– , x -> this.equals(x)



. super



. super::instanceMethod



this



. , :

class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }





Runnable



, super::speak



, speak



. ( , , EnclosingClass.this::method



EnclosingClass.super::method



.)





, , , new



. , Button::new



Button



. ? . , . , , , :

List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());





stream



, map



collect



. , , map



Button(String)



. Button



, , , , .



. , int[]::new



: . - x -> new int[x]



.



Java. T. new T[n]



, new Object[n]



. . , , . Stream



toArray



, Object



:

Object[] buttons = stream.toArray();





. , . . Button[]::new



toArray



:

Button[] buttons = stream.toArray(Button[]::new);





toArray



. .





-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



.



, , . - repeatText



. text



count



?



, , -. - :



; , ,

- , text



count



. , -, , , "Hi!" 2000. , -. ( , . , - , .)



. - , , , Java . Java - . , . Java 8 .



, - . Java, , , . - , . , :

public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



. -. final



; , , .



, . . matchCount



– , , .



, , . ,

List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





, matchedObjs



final



. ( final



, .) matchedObjs



ArrayList



. , . add



, .



. . .



, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



- this



, . , ,

public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }





this.toString()



toString



Application



, Runnable



. this



-. - doWork



, this



.





. , , , . , :

for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));





. forEach



, .

strList.forEach(System.out::println);





, . Java , . Collection



, forEach



, , , Collection



, , . Java.



Java , ( ). . . Java 8 forEach



Iterable



, Collection



, , .



:

interface Person { long getId(); default String getFirstName() { return "Jack"; } }





: getId



, , getFirstName



. , Person



, , , getId



, , getFirstName



.



, , , Collection/AbstractCollection



WindowListener/WindowAdapter



. .

, , ? C++ . , Java . :



. , . . , ( ), .

. getFirstName



:

interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }





, , ?

class Student implements Person, Naming { ... }





getFirstName



, Person



Naming



. , Java . getFirstName



Student



. , :

class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }





, Naming



getFirstName



:

interface Naming { String getFirstName(); }





Student



Person



? , Java . , . , , .



, -Java 8 . : . .



. , , . , , Person



Student



:

class Student extends Person implements Naming { ... }





, . Student



getFirstName



Person



, , Naming



getFirstName



. « » . « » Java 7. , , , . : , Object



. , toString



equals



, , List



. , Object.toString



Object.equals



.





- , - Java, - , . ? Java , . , , , . , , Java 8.











लागू करती है Comparator . compare -. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



, - , - Java. , , , (String, String) -> int



, , . Java - Object



, Object



. Java , .



Java API java.util.function. , BiFunction <T, U, R>



, U R. :

BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());





, . Arrays.sort



, BiFunction



. , . Java . , Comparator



, , . Java 8 . - - , , .



java.util.function Java 8 API , , , . , - , API, . , @FunctionalInterface



. . , . Javadoc , . . , , . @FunctionalInterface



- .



, , checked . - checked , . , :

Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





Runnable.run



, . , . -. , . , call



Callable



. , Callable ( return null



).





, , . , , event



, . ,

button.setOnAction(event -> System.out.println(event));





, println



setOnAction



. :

button.setOnAction(System.out::println);





System.out::println



, - x -> System.out.println(x)



.



, , . :

Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



-, . , System.out::println



x -> System.out.println(x)



. , Math::pow



(x, y) -> Math.pow(x, y)



. . , String::compareToIgnoreCase



- , (x, y) -> x.compareToIgnoreCase(y)



.



, . , Math.max



, int



double



. , , Math.max



. , -, . .



this



. , this::equals



– , x -> this.equals(x)



. super



. super::instanceMethod



this



. , :

class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }





Runnable



, super::speak



, speak



. ( , , EnclosingClass.this::method



EnclosingClass.super::method



.)





, , , new



. , Button::new



Button



. ? . , . , , , :

List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());





stream



, map



collect



. , , map



Button(String)



. Button



, , , , .



. , int[]::new



: . - x -> new int[x]



.



Java. T. new T[n]



, new Object[n]



. . , , . Stream



toArray



, Object



:

Object[] buttons = stream.toArray();





. , . . Button[]::new



toArray



:

Button[] buttons = stream.toArray(Button[]::new);





toArray



. .





-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



.



, , . - repeatText



. text



count



?



, , -. - :



; , ,

- , text



count



. , -, , , "Hi!" 2000. , -. ( , . , - , .)



. - , , , Java . Java - . , . Java 8 .



, - . Java, , , . - , . , :

public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



. -. final



; , , .



, . . matchCount



– , , .



, , . ,

List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





, matchedObjs



final



. ( final



, .) matchedObjs



ArrayList



. , . add



, .



. . .



, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



- this



, . , ,

public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }





this.toString()



toString



Application



, Runnable



. this



-. - doWork



, this



.





. , , , . , :

for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));





. forEach



, .

strList.forEach(System.out::println);





, . Java , . Collection



, forEach



, , , Collection



, , . Java.



Java , ( ). . . Java 8 forEach



Iterable



, Collection



, , .



:

interface Person { long getId(); default String getFirstName() { return "Jack"; } }





: getId



, , getFirstName



. , Person



, , , getId



, , getFirstName



.



, , , Collection/AbstractCollection



WindowListener/WindowAdapter



. .

, , ? C++ . , Java . :



. , . . , ( ), .

. getFirstName



:

interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }





, , ?

class Student implements Person, Naming { ... }





getFirstName



, Person



Naming



. , Java . getFirstName



Student



. , :

class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }





, Naming



getFirstName



:

interface Naming { String getFirstName(); }





Student



Person



? , Java . , . , , .



, -Java 8 . : . .



. , , . , , Person



Student



:

class Student extends Person implements Naming { ... }





, . Student



getFirstName



Person



, , Naming



getFirstName



. « » . « » Java 7. , , , . : , Object



. , toString



equals



, , List



. , Object.toString



Object.equals



.





- , - Java, - , . ? Java , . , , , . , , Java 8.











Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



, - , - Java. , , , (String, String) -> int



, , . Java - Object



, Object



. Java , .



Java API java.util.function. , BiFunction <T, U, R>



, U R. :

BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());





, . Arrays.sort



, BiFunction



. , . Java . , Comparator



, , . Java 8 . - - , , .



java.util.function Java 8 API , , , . , - , API, . , @FunctionalInterface



. . , . Javadoc , . . , , . @FunctionalInterface



- .



, , checked . - checked , . , :

Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





Runnable.run



, . , . -. , . , call



Callable



. , Callable ( return null



).





, , . , , event



, . ,

button.setOnAction(event -> System.out.println(event));





, println



setOnAction



. :

button.setOnAction(System.out::println);





System.out::println



, - x -> System.out.println(x)



.



, , . :

Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



-, . , System.out::println



x -> System.out.println(x)



. , Math::pow



(x, y) -> Math.pow(x, y)



. . , String::compareToIgnoreCase



- , (x, y) -> x.compareToIgnoreCase(y)



.



, . , Math.max



, int



double



. , , Math.max



. , -, . .



this



. , this::equals



– , x -> this.equals(x)



. super



. super::instanceMethod



this



. , :

class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }





Runnable



, super::speak



, speak



. ( , , EnclosingClass.this::method



EnclosingClass.super::method



.)





, , , new



. , Button::new



Button



. ? . , . , , , :

List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());





stream



, map



collect



. , , map



Button(String)



. Button



, , , , .



. , int[]::new



: . - x -> new int[x]



.



Java. T. new T[n]



, new Object[n]



. . , , . Stream



toArray



, Object



:

Object[] buttons = stream.toArray();





. , . . Button[]::new



toArray



:

Button[] buttons = stream.toArray(Button[]::new);





toArray



. .





-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



.



, , . - repeatText



. text



count



?



, , -. - :



; , ,

- , text



count



. , -, , , "Hi!" 2000. , -. ( , . , - , .)



. - , , , Java . Java - . , . Java 8 .



, - . Java, , , . - , . , :

public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



. -. final



; , , .



, . . matchCount



– , , .



, , . ,

List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





, matchedObjs



final



. ( final



, .) matchedObjs



ArrayList



. , . add



, .



. . .



, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



- this



, . , ,

public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }





this.toString()



toString



Application



, Runnable



. this



-. - doWork



, this



.





. , , , . , :

for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));





. forEach



, .

strList.forEach(System.out::println);





, . Java , . Collection



, forEach



, , , Collection



, , . Java.



Java , ( ). . . Java 8 forEach



Iterable



, Collection



, , .



:

interface Person { long getId(); default String getFirstName() { return "Jack"; } }





: getId



, , getFirstName



. , Person



, , , getId



, , getFirstName



.



, , , Collection/AbstractCollection



WindowListener/WindowAdapter



. .

, , ? C++ . , Java . :



. , . . , ( ), .

. getFirstName



:

interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }





, , ?

class Student implements Person, Naming { ... }





getFirstName



, Person



Naming



. , Java . getFirstName



Student



. , :

class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }





, Naming



getFirstName



:

interface Naming { String getFirstName(); }





Student



Person



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     button.setOnAction(event -> System.out.println("The button has been clicked!"));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     ,       U     R.           : 
      

        
        
        
      

     BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     .    .  ,          .   Javadoc    ,      .     .       ,  ,  .    @FunctionalInterface
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      Runnable.run
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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        ,     ,        . , ,        event
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     button.setOnAction(event -> System.out.println(event));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       ,        println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       setOnAction
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     button.setOnAction(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      System.out::println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        ,   - x -> System.out.println(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     object::instanceMethod Class::staticMethod Class::instanceMethod 
      

        
        
        
      

     
      

        
        
        
      

             -,    .   , System.out::println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     ,   int
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     .  ,   -,       .       . 
      

        
        
        
      

     
      

        
        
        
      

         this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        . , this::equals
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     –   ,   x -> this.equals(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    super
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  super::instanceMethod
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             .   ,   : 
      

        
        
        
      

     class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          Runnable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  super::speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ( ,            ,  EnclosingClass.this::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      EnclosingClass.super::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .) 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

         ,    ,   ,     new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . , Button::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    ?    . ,     . ,       ,       ,    : 
      

        
        
        
      

     List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       collect
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         .   ,  ,   map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Button(String)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        .    Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,     ,     ,     . 
      

        
        
        
      

     
      

        
        
        
      

             . , int[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
           :  .   - x -> new int[x]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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             Java.      T.  new T[n]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      ,      new Object[n]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      . , ,     .  Stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   Object
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     Object[] buttons = stream.toArray();
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       .    ,   .          .  Button[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     Button[] buttons = stream.toArray(Button[]::new);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
            .      . 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

                     -.   : 
      

        
        
        
      

     public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      : 
      

        
        
        
      

     repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      text
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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       ,   ,   .  -      repeatText
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          .    text
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,  -,      ,    , "Hi!"  2000.  ,      -. (   ,   . ,   -     ,           .) 
      

        
        
        
      

     
      

        
        
        
      

                .  - ,     ,  ,  Java   .  Java -  .   ,       . Java 8      . 
      

        
        
        
      

     
      

        
        
        
      

       , -       .  Java,  ,    ,   .  -     ,    . ,    : 
      

        
        
        
      

     public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         .    -  .    ,      . 
      

        
        
        
      

     int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          ,      .  matchCount++
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,     ,  ,       . 
      

        
        
        
      

     
      

        
        
        
      

             .  Java 8         final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .         -.         final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      ;  ,   ,    . 
      

        
        
        
      

     
      

        
        
        
      

      ,       .         .  matchCount
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     –        ,     ,      . 
      

        
        
        
      

     
      

        
        
        
      

      ,     ,      . , 
      

        
        
        
      

     List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,   matchedObjs
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ( final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       ,         .)    matchedObjs
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             ArrayList
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .   ,    .      add
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    . 
      

        
        
        
      

     
      

        
        
        
      

            .          .          . 
      

        
        
        
      

     
      

        
        
        
      

         ,   ,   -       .    1,  : 
      

        
        
        
      

     int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

     ,    .        ,   ,    ,     . 
      

        
        
        
      

     
      

        
        
        
      

      -     ,    .         .        ,     ,    . 
      

        
        
        
      

     Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

                 .  ,          -.     this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -     this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   . , ,   
      

        
        
        
      

     public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      this.toString()
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       toString
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Application
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    Runnable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -.   -    doWork
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             . 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

              .     ,      ,  ,  . ,  : 
      

        
        
        
      

     for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       .      forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,      .      
      

        
        
        
      

     strList.forEach(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,       .    Java     ,   .   Collection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       ,   forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   ,     ,  Collection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , ,      .     Java. 
      

        
        
        
      

     
      

        
        
        
      

      Java      ,        (    ).         .          .  Java 8  forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         Iterable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  Collection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  ,    . 
      

        
        
        
      

     
      

        
        
        
      

       : 
      

        
        
        
      

     interface Person { long getId(); default String getFirstName() { return "Jack"; } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        : getId
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   ,     getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,   Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , , ,   getId
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,   getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       . 
      

        
        
        
      

     
      

        
        
        
      

                ,         , ,  Collection/AbstractCollection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      WindowListener/WindowAdapter
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .        . 
      

        
        
        
      

      ,             ,          ?     C++      .  ,   Java  .  : 
      

        
        
        
      

     
      

        
        
        
      

       .     ,            .  .       ,             (   ),         . 
      

        
        
        
      

         .       getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,    ,  ? 
      

        
        
        
      

     class Student implements Person, Naming { ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

           getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Naming
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      ,  Java        .    getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Student
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .           ,   : 
      

        
        
        
      

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-. , - , . - , , , .



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button.setOnAction(event -> System.out.println("The button has been clicked!"));





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count



text



-. , -. , repeatText



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?



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; , ,

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public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





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, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



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     button.setOnAction(event -> System.out.println("The button has been clicked!"));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         . 
      

        
        
        
      

     
      

        
        
        
      

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     ,       U     R.           : 
      

        
        
        
      

     BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     .  : 
      

        
        
        
      

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     object::instanceMethod Class::staticMethod Class::instanceMethod 
      

        
        
        
      

     
      

        
        
        
      

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     .         .  , String::compareToIgnoreCase
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     .     ,      ,   Math.max
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,   -,       .       . 
      

        
        
        
      

     
      

        
        
        
      

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        . , this::equals
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     –   ,   x -> this.equals(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    super
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  super::instanceMethod
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             .   ,   : 
      

        
        
        
      

     class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          Runnable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  super::speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ( ,            ,  EnclosingClass.this::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      EnclosingClass.super::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .) 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

         ,    ,   ,     new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . , Button::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    ?    . ,     . ,       ,       ,    : 
      

        
        
        
      

     List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       collect
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         .   ,  ,   map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Button(String)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        .    Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,     ,     ,     . 
      

        
        
        
      

     
      

        
        
        
      

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     . 
      

        
        
        
      

     
      

        
        
        
      

             Java.      T.  new T[n]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      ,      new Object[n]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      . , ,     .  Stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   Object
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     Object[] buttons = stream.toArray();
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       .    ,   .          .  Button[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     Button[] buttons = stream.toArray(Button[]::new);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
            .      . 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

                     -.   : 
      

        
        
        
      

     public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      : 
      

        
        
        
      

     repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      text
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -.  ,       -.  ,     repeatText
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

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      count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,  -,      ,    , "Hi!"  2000.  ,      -. (   ,   . ,   -     ,           .) 
      

        
        
        
      

     
      

        
        
        
      

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     : 
      

        
        
        
      

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Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





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:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



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. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





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 Comparator .   compare
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          -.         ,     -   ,     .     -   ,    ,  ,       . 
      

        
        
        
      

     
      

        
        
        
      

         –  ,   -  .    .    : 
      

        
        
        
      

     button.setOnAction(event -> System.out.println("The button has been clicked!"));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     ,       U     R.           : 
      

        
        
        
      

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     , ,  checked          .   -   checked ,          . ,    : 
      

        
        
        
      

     Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     ). 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

        ,     ,        . , ,        event
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   . ,     
      

        
        
        
      

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       ,        println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       setOnAction
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  : 
      

        
        
        
      

     button.setOnAction(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      System.out::println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        ,   - x -> System.out.println(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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        , ,         .     : 
      

        
        
        
      

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     object::instanceMethod Class::staticMethod Class::instanceMethod 
      

        
        
        
      

     
      

        
        
        
      

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      x -> System.out.println(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     -    ,   (x, y) -> x.compareToIgnoreCase(y)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     .  ,   -,       .       . 
      

        
        
        
      

     
      

        
        
        
      

         this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     –   ,   x -> this.equals(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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      EnclosingClass.super::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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         ,    ,   ,     new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . , Button::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    ?    . ,     . ,       ,       ,    : 
      

        
        
        
      

     List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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       Button(String)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        .    Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     Object[] buttons = stream.toArray();
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       .    ,   .          .  Button[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     Button[] buttons = stream.toArray(Button[]::new);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
            .      . 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

                     -.   : 
      

        
        
        
      

     public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      : 
      

        
        
        
      

     repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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      text
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -.  ,       -.  ,     repeatText
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     .  ,  -,      ,    , "Hi!"  2000.  ,      -. (   ,   . ,   -     ,           .) 
      

        
        
        
      

     
      

        
        
        
      

                .  - ,     ,  ,  Java   .  Java -  .   ,       . Java 8      . 
      

        
        
        
      

     
      

        
        
        
      

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     public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         .    -  .    ,      . 
      

        
        
        
      

     int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          ,      .  matchCount++
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,     ,  ,       . 
      

        
        
        
      

     
      

        
        
        
      

             .  Java 8         final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .         -.         final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      ;  ,   ,    . 
      

        
        
        
      

     
      

        
        
        
      

      ,       .         .  matchCount
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      ,     ,      . , 
      

        
        
        
      

     List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,   matchedObjs
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ( final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       ,         .)    matchedObjs
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             ArrayList
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .   ,    .      add
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    . 
      

        
        
        
      

     
      

        
        
        
      

            .          .          . 
      

        
        
        
      

     
      

        
        
        
      

         ,   ,   -       .    1,  : 
      

        
        
        
      

     int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

     ,    .        ,   ,    ,     . 
      

        
        
        
      

     
      

        
        
        
      

      -     ,    .         .        ,     ,    . 
      

        
        
        
      

     Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

                 .  ,          -.     this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     ,   . , ,   
      

        
        
        
      

     public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      this.toString()
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       toString
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Application
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    Runnable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -.   -    doWork
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             . 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

              .     ,      ,  ,  . ,  : 
      

        
        
        
      

     for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       .      forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,      .      
      

        
        
        
      

     strList.forEach(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,       .    Java     ,   .   Collection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       ,   forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   ,     ,  Collection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , ,      .     Java. 
      

        
        
        
      

     
      

        
        
        
      

      Java      ,        (    ).         .          .  Java 8  forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         Iterable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     ,  ,    . 
      

        
        
        
      

     
      

        
        
        
      

       : 
      

        
        
        
      

     interface Person { long getId(); default String getFirstName() { return "Jack"; } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        : getId
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   ,     getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,   Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , , ,   getId
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,   getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       . 
      

        
        
        
      

     
      

        
        
        
      

                ,         , ,  Collection/AbstractCollection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      WindowListener/WindowAdapter
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .        . 
      

        
        
        
      

      ,             ,          ?     C++      .  ,   Java  .  : 
      

        
        
        
      

     
      

        
        
        
      

       .     ,            .  .       ,             (   ),         . 
      

        
        
        
      

         .       getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,    ,  ? 
      

        
        
        
      

     class Student implements Person, Naming { ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

           getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Naming
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      ,  Java        .    getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Student
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .           ,   : 
      

        
        
        
      

     class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,  Naming
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
            getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     interface Naming { String getFirstName(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        Student
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
           Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ?     ,   Java     .    ,    .       ,    ,     . 
      

        
        
        
      

     
      

        
        
        
      

                ,     -Java 8     .      :      .       . 
      

        
        
        
      

     
      

        
        
        
      

             .   ,     ,      . , ,  Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        Student
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      : 
      

        
        
        
      

     class Student extends Person implements Naming { ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

            ,          .    Student
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,    Naming
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      .   « »  .  « »    Java 7.        ,       ,    ,     .    :        ,       Object
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ,         toString
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     ,         ,  List
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      ,        Object.toString
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Object.equals
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

      
      

        
        
        
      

          -        , -   Java, - ,   .   ?    Java ,           .    , ,    ,         . ,      ,      Java 8.
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     

Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



, - , - Java. , , , (String, String) -> int



, , . Java - Object



, Object



. Java , .



Java API java.util.function. , BiFunction <T, U, R>



, U R. :

BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());





, . Arrays.sort



, BiFunction



. , . Java . , Comparator



, , . Java 8 . - - , , .



java.util.function Java 8 API , , , . , - , API, . , @FunctionalInterface



. . , . Javadoc , . . , , . @FunctionalInterface



- .



, , checked . - checked , . , :

Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





Runnable.run



, . , . -. , . , call



Callable



. , Callable ( return null



).





, , . , , event



, . ,

button.setOnAction(event -> System.out.println(event));





, println



setOnAction



. :

button.setOnAction(System.out::println);





System.out::println



, - x -> System.out.println(x)



.



, , . :

Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



-, . , System.out::println



x -> System.out.println(x)



. , Math::pow



(x, y) -> Math.pow(x, y)



. . , String::compareToIgnoreCase



- , (x, y) -> x.compareToIgnoreCase(y)



.



, . , Math.max



, int



double



. , , Math.max



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this



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this



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class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }





Runnable



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, speak



. ( , , EnclosingClass.this::method



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, , , new



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stream



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, , , , .



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Button[] buttons = stream.toArray(Button[]::new);





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. .





-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



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. , -, , , "Hi!" 2000. , -. ( , . , - , .)



. - , , , Java . Java - . , . Java 8 .



, - . Java, , , . - , . , :

public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



. -. final



; , , .



, . . matchCount



– , , .



, , . ,

List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





, matchedObjs



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. ( final



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. , . add



, .



. . .



, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



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public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }





this.toString()



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.





. , , , . , :

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Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





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Runnable



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. ( , , EnclosingClass.this::method



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Button



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Button[] buttons = stream.toArray(Button[]::new);





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-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



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. , -, , , "Hi!" 2000. , -. ( , . , - , .)



. - , , , Java . Java - . , . Java 8 .



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public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



. -. final



; , , .



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List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





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int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



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Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





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interface Person { long getId(); default String getFirstName() { return "Jack"; } }





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getFirstName



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class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }





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interface Naming { String getFirstName(); }





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button.setOnAction(event -> System.out.println("The button has been clicked!"));





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Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





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button.setOnAction(event -> System.out.println(event));





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Arrays.sort(strs, String::compareToIgnoreCase)





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object::instanceMethod Class::staticMethod Class::instanceMethod



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x -> System.out.println(x)



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Runnable



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. , Button::new



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. ? . , . , , , :

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Object[] buttons = stream.toArray();





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:

Button[] buttons = stream.toArray(Button[]::new);





toArray



. .





-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



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, , . - repeatText



. text



count



?



, , -. - :



; , ,

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. , -, , , "Hi!" 2000. , -. ( , . , - , .)



. - , , , Java . Java - . , . Java 8 .



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public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



. -. final



; , , .



, . . matchCount



– , , .



, , . ,

List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





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final



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. , . add



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, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



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Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



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public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }





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. , , , . , :

for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));





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strList.forEach(System.out::println);





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, , ? C++ . , Java . :



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. , :

class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }





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interface Naming { String getFirstName(); }





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      : 
      

        
        
        
      

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       : 
      

        
        
        
      

     interface Person { long getId(); default String getFirstName() { return "Jack"; } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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                ,         , ,  Collection/AbstractCollection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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-. , - , . - , , , .



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button.setOnAction(event -> System.out.println("The button has been clicked!"));





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count



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. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





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     button.setOnAction(event -> System.out.println("The button has been clicked!"));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     .  : 
      

        
        
        
      

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     object::instanceMethod Class::staticMethod Class::instanceMethod 
      

        
        
        
      

     
      

        
        
        
      

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        double
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .     ,      ,   Math.max
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,   -,       .       . 
      

        
        
        
      

     
      

        
        
        
      

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        . , this::equals
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     –   ,   x -> this.equals(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    super
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  super::instanceMethod
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             .   ,   : 
      

        
        
        
      

     class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          Runnable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  super::speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ( ,            ,  EnclosingClass.this::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      EnclosingClass.super::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .) 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

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     . , Button::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    ?    . ,     . ,       ,       ,    : 
      

        
        
        
      

     List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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       collect
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         .   ,  ,   map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Button(String)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        .    Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,     ,     ,     . 
      

        
        
        
      

     
      

        
        
        
      

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      ,      new Object[n]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      . , ,     .  Stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   Object
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     Object[] buttons = stream.toArray();
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       .    ,   .          .  Button[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     Button[] buttons = stream.toArray(Button[]::new);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
            .      . 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

                     -.   : 
      

        
        
        
      

     public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      : 
      

        
        
        
      

     repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      text
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -.  ,       -.  ,     repeatText
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

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. - . , .

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button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



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button.setOnAction(event -> System.out.println(event));





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Button[] buttons = stream.toArray(Button[]::new);





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. .





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public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



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public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



. -. final



; , , .



, . . matchCount



– , , .



, , . ,

List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





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final



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, . , , , .



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int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





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public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





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-. , -. , repeatText



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. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





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, , - . 1, :

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, . , , , .



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Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



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     button.setOnAction(event -> System.out.println(event));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     button.setOnAction(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      System.out::println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     –   ,   x -> this.equals(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          Runnable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      EnclosingClass.super::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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          Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    ?    . ,     . ,       ,       ,    : 
      

        
        
        
      

     List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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         .   ,  ,   map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Button(String)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        .    Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,     ,     ,     . 
      

        
        
        
      

     
      

        
        
        
      

             . , int[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
           :  .   - x -> new int[x]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      ,      new Object[n]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      . , ,     .  Stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     : 
      

        
        
        
      

     Object[] buttons = stream.toArray();
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       .    ,   .          .  Button[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     Button[] buttons = stream.toArray(Button[]::new);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
            .      . 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

                     -.   : 
      

        
        
        
      

     public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      : 
      

        
        
        
      

     repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      text
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -.  ,       -.  ,     repeatText
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

       ,   ,   .  -      repeatText
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          .    text
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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           ;  , ,          
      

        
        
        
      

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      count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,  -,      ,    , "Hi!"  2000.  ,      -. (   ,   . ,   -     ,           .) 
      

        
        
        
      

     
      

        
        
        
      

                .  - ,     ,  ,  Java   .  Java -  .   ,       . Java 8      . 
      

        
        
        
      

     
      

        
        
        
      

       , -       .  Java,  ,    ,   .  -     ,    . ,    : 
      

        
        
        
      

     public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         .    -  .    ,      . 
      

        
        
        
      

     int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          ,      .  matchCount++
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,     ,  ,       . 
      

        
        
        
      

     
      

        
        
        
      

             .  Java 8         final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .         -.         final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      ;  ,   ,    . 
      

        
        
        
      

     
      

        
        
        
      

      ,       .         .  matchCount
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      ,     ,      . , 
      

        
        
        
      

     List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,   matchedObjs
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ( final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       ,         .)    matchedObjs
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             ArrayList
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .   ,    .      add
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    . 
      

        
        
        
      

     
      

        
        
        
      

            .          .          . 
      

        
        
        
      

     
      

        
        
        
      

         ,   ,   -       .    1,  : 
      

        
        
        
      

     int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

     ,    .        ,   ,    ,     . 
      

        
        
        
      

     
      

        
        
        
      

      -     ,    .         .        ,     ,    . 
      

        
        
        
      

     Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

                 .  ,          -.     this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -     this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   . , ,   
      

        
        
        
      

     public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      this.toString()
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       toString
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Application
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    Runnable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -.   -    doWork
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             . 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

              .     ,      ,  ,  . ,  : 
      

        
        
        
      

     for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       .      forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,      .      
      

        
        
        
      

     strList.forEach(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,       .    Java     ,   .   Collection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       ,   forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   ,     ,  Collection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , ,      .     Java. 
      

        
        
        
      

     
      

        
        
        
      

      Java      ,        (    ).         .          .  Java 8  forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         Iterable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  Collection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  ,    . 
      

        
        
        
      

     
      

        
        
        
      

       : 
      

        
        
        
      

     interface Person { long getId(); default String getFirstName() { return "Jack"; } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        : getId
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   ,     getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,   Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , , ,   getId
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,   getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       . 
      

        
        
        
      

     
      

        
        
        
      

                ,         , ,  Collection/AbstractCollection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      WindowListener/WindowAdapter
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .        . 
      

        
        
        
      

      ,             ,          ?     C++      .  ,   Java  .  : 
      

        
        
        
      

     
      

        
        
        
      

       .     ,            .  .       ,             (   ),         . 
      

        
        
        
      

         .       getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,    ,  ? 
      

        
        
        
      

     class Student implements Person, Naming { ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

           getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Naming
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      ,  Java        .    getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Student
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .           ,   : 
      

        
        
        
      

     class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,  Naming
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
            getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     interface Naming { String getFirstName(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        Student
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
           Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ?     ,   Java     .    ,    .       ,    ,     . 
      

        
        
        
      

     
      

        
        
        
      

                ,     -Java 8     .      :      .       . 
      

        
        
        
      

     
      

        
        
        
      

             .   ,     ,      . , ,  Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        Student
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      : 
      

        
        
        
      

     class Student extends Person implements Naming { ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

            ,          .    Student
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,    Naming
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      .   « »  .  « »    Java 7.        ,       ,    ,     .    :        ,       Object
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ,         toString
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      equals
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,         ,  List
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      ,        Object.toString
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Object.equals
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

      
      

        
        
        
      

          -        , -   Java, - ,   .   ?    Java ,           .    , ,    ,         . ,      ,      Java 8.
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     

Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



, - , - Java. , , , (String, String) -> int



, , . Java - Object



, Object



. Java , .



Java API java.util.function. , BiFunction <T, U, R>



, U R. :

BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());





, . Arrays.sort



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java.util.function Java 8 API , , , . , - , API, . , @FunctionalInterface



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- .



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Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





Runnable.run



, . , . -. , . , call



Callable



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).





, , . , , event



, . ,

button.setOnAction(event -> System.out.println(event));





, println



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. :

button.setOnAction(System.out::println);





System.out::println



, - x -> System.out.println(x)



.



, , . :

Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



-, . , System.out::println



x -> System.out.println(x)



. , Math::pow



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, . , Math.max



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. , , Math.max



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class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }





Runnable



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, speak



. ( , , EnclosingClass.this::method



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, , , new



. , Button::new



Button



. ? . , . , , , :

List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());





stream



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collect



. , , map



Button(String)



. Button



, , , , .



. , int[]::new



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Java. T. new T[n]



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Object[] buttons = stream.toArray();





. , . . Button[]::new



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:

Button[] buttons = stream.toArray(Button[]::new);





toArray



. .





-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



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, , . - repeatText



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count



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, , -. - :



; , ,

- , text



count



. , -, , , "Hi!" 2000. , -. ( , . , - , .)



. - , , , Java . Java - . , . Java 8 .



, - . Java, , , . - , . , :

public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



. -. final



; , , .



, . . matchCount



– , , .



, , . ,

List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





, matchedObjs



final



. ( final



, .) matchedObjs



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. , . add



, .



. . .



, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



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public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }





this.toString()



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.





. , , , . , :

for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));





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interface Person { long getId(); default String getFirstName() { return "Jack"; } }





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class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }





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interface Naming { String getFirstName(); }





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Comparator . compare



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BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());





, . Arrays.sort



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. , . Java . , Comparator



, , . Java 8 . - - , , .



java.util.function Java 8 API , , , . , - , API, . , @FunctionalInterface



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Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





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, . , . -. , . , call



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button.setOnAction(event -> System.out.println(event));





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. :

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.



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Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



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x -> System.out.println(x)



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. ( , , EnclosingClass.this::method



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, , , new



. , Button::new



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. ? . , . , , , :

List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());





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:

Button[] buttons = stream.toArray(Button[]::new);





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. .





-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



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. text



count



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, , -. - :



; , ,

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count



. , -, , , "Hi!" 2000. , -. ( , . , - , .)



. - , , , Java . Java - . , . Java 8 .



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public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



. -. final



; , , .



, . . matchCount



– , , .



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List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





, matchedObjs



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. , . add



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int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



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Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





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interface Person { long getId(); default String getFirstName() { return "Jack"; } }





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. .

, , ? C++ . , Java . :



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interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }





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class Student implements Person, Naming { ... }





getFirstName



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Student



. , :

class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }





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getFirstName



:

interface Naming { String getFirstName(); }





Student



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? , Java . , . , , .



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class Student extends Person implements Naming { ... }





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getFirstName



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Comparator . compare



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button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



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Java API java.util.function. , BiFunction <T, U, R>



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BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());





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. , . Java . , Comparator



, , . Java 8 . - - , , .



java.util.function Java 8 API , , , . , - , API, . , @FunctionalInterface



. . , . Javadoc , . . , , . @FunctionalInterface



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Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





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, . , . -. , . , call



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button.setOnAction(event -> System.out.println(event));





, println



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. :

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System.out::println



, - x -> System.out.println(x)



.



, , . :

Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



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x -> System.out.println(x)



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(x, y) -> Math.pow(x, y)



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- , (x, y) -> x.compareToIgnoreCase(y)



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. , , Math.max



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class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }





Runnable



, super::speak



, speak



. ( , , EnclosingClass.this::method



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, , , new



. , Button::new



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. ? . , . , , , :

List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());





stream



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. Button



, , , , .



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Java. T. new T[n]



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:

Object[] buttons = stream.toArray();





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:

Button[] buttons = stream.toArray(Button[]::new);





toArray



. .





-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



.



, , . - repeatText



. text



count



?



, , -. - :



; , ,

- , text



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. , -, , , "Hi!" 2000. , -. ( , . , - , .)



. - , , , Java . Java - . , . Java 8 .



, - . Java, , , . - , . , :

public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



. -. final



; , , .



, . . matchCount



– , , .



, , . ,

List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





, matchedObjs



final



. ( final



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ArrayList



. , . add



, .



. . .



, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



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, . , ,

public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }





this.toString()



toString



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. this



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.





. , , , . , :

for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));





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, .

strList.forEach(System.out::println);





, . Java , . Collection



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, , . Java.



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, , .



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interface Person { long getId(); default String getFirstName() { return "Jack"; } }





: getId



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. .

, , ? C++ . , Java . :



. , . . , ( ), .

. getFirstName



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interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }





, , ?

class Student implements Person, Naming { ... }





getFirstName



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. , Java . getFirstName



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. , :

class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }





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:

interface Naming { String getFirstName(); }





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? , Java . , . , , .



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class Student extends Person implements Naming { ... }





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 Comparator .   compare
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     .  : 
      

        
        
        
      

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        ,   - x -> System.out.println(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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       : 
      

        
        
        
      

     interface Person { long getId(); default String getFirstName() { return "Jack"; } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     : 
      

        
        
        
      

     interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





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button.setOnAction(event -> System.out.println(event));





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:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



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toArray



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-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



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public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





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int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





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     .  ,   Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , , ,   getId
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,   getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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                ,         , ,  Collection/AbstractCollection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      ,             ,          ?     C++      .  ,   Java  .  : 
      

        
        
        
      

     
      

        
        
        
      

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     interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     class Student implements Person, Naming { ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     .           ,   : 
      

        
        
        
      

     class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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      .   « »  .  « »    Java 7.        ,       ,    ,     .    :        ,       Object
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



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. Java , .



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.



, , . :

Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



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x -> System.out.println(x)



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.



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Runnable



, super::speak



, speak



. ( , , EnclosingClass.this::method



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Button[] buttons = stream.toArray(Button[]::new);





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-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



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. - , , , Java . Java - . , . Java 8 .



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public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





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. Java 8 final



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List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





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final



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int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



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Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



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interface Naming { String getFirstName(); }





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 Comparator .   compare
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          -.         ,     -   ,     .     -   ,    ,  ,       . 
      

        
        
        
      

     
      

        
        
        
      

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     button.setOnAction(event -> System.out.println("The button has been clicked!"));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         . 
      

        
        
        
      

     
      

        
        
        
      

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     Java API        java.util.function.   , BiFunction <T, U, R>
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,       U     R.           : 
      

        
        
        
      

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     .    .  ,          .   Javadoc    ,      .     .       ,  ,  .    @FunctionalInterface
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     -   . 
      

        
        
        
      

     
      

        
        
        
      

     , ,  checked          .   -   checked ,          . ,    : 
      

        
        
        
      

     Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      Runnable.run
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        ,    .   ,     .       -.      ,       . ,  call
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     ). 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

        ,     ,        . , ,        event
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   . ,     
      

        
        
        
      

     button.setOnAction(event -> System.out.println(event));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       ,        println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       setOnAction
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  : 
      

        
        
        
      

     button.setOnAction(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      System.out::println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        ,   - x -> System.out.println(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

        , ,         .     : 
      

        
        
        
      

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             ::        .    : 
      

        
        
        
      

     
      

        
        
        
      

     object::instanceMethod Class::staticMethod Class::instanceMethod 
      

        
        
        
      

     
      

        
        
        
      

             -,    .   , System.out::println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      x -> System.out.println(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .   , Math::pow
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      (x, y) -> Math.pow(x, y)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .         .  , String::compareToIgnoreCase
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     -    ,   (x, y) -> x.compareToIgnoreCase(y)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

                  ,     . ,     Math.max
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   int
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        double
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .     ,      ,   Math.max
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,   -,       .       . 
      

        
        
        
      

     
      

        
        
        
      

         this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        . , this::equals
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     –   ,   x -> this.equals(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    super
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  super::instanceMethod
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             .   ,   : 
      

        
        
        
      

     class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          Runnable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  super::speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ( ,            ,  EnclosingClass.this::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      EnclosingClass.super::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .) 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

         ,    ,   ,     new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . , Button::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    ?    . ,     . ,       ,       ,    : 
      

        
        
        
      

     List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       collect
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         .   ,  ,   map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Button(String)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        .    Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,     ,     ,     . 
      

        
        
        
      

     
      

        
        
        
      

             . , int[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
           :  .   - x -> new int[x]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

             Java.      T.  new T[n]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      ,      new Object[n]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      . , ,     .  Stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   Object
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     Object[] buttons = stream.toArray();
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       .    ,   .          .  Button[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

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button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



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. .





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:

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:

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. - . , .

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     : 
      

        
        
        
      

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Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





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:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



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. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





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 Comparator .   compare
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          -.         ,     -   ,     .     -   ,    ,  ,       . 
      

        
        
        
      

     
      

        
        
        
      

         –  ,   -  .    .    : 
      

        
        
        
      

     button.setOnAction(event -> System.out.println("The button has been clicked!"));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     ,       U     R.           : 
      

        
        
        
      

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     , ,  checked          .   -   checked ,          . ,    : 
      

        
        
        
      

     Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     ). 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

        ,     ,        . , ,        event
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   . ,     
      

        
        
        
      

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       ,        println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       setOnAction
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  : 
      

        
        
        
      

     button.setOnAction(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      System.out::println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        ,   - x -> System.out.println(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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        , ,         .     : 
      

        
        
        
      

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     class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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          Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    ?    . ,     . ,       ,       ,    : 
      

        
        
        
      

     List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     Button[] buttons = stream.toArray(Button[]::new);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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                     -.   : 
      

        
        
        
      

     public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      : 
      

        
        
        
      

     repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread 
      

        
        
        
      

         count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     .  ,  -,      ,    , "Hi!"  2000.  ,      -. (   ,   . ,   -     ,           .) 
      

        
        
        
      

     
      

        
        
        
      

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     public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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             .  Java 8         final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      ,       .         .  matchCount
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,   matchedObjs
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     . ( final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       ,         .)    matchedObjs
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             ArrayList
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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         ,   ,   -       .    1,  : 
      

        
        
        
      

     int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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      -     ,    .         .        ,     ,    . 
      

        
        
        
      

     Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

                 .  ,          -.     this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      this.toString()
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       toString
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      -.   -    doWork
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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             . 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

              .     ,      ,  ,  . ,  : 
      

        
        
        
      

     for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     ,      .      
      

        
        
        
      

     strList.forEach(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,       .    Java     ,   .   Collection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       ,   forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      Java      ,        (    ).         .          .  Java 8  forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         Iterable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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       : 
      

        
        
        
      

     interface Person { long getId(); default String getFirstName() { return "Jack"; } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        : getId
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   ,     getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,   Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , , ,   getId
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,   getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       . 
      

        
        
        
      

     
      

        
        
        
      

                ,         , ,  Collection/AbstractCollection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      WindowListener/WindowAdapter
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      ,             ,          ?     C++      .  ,   Java  .  : 
      

        
        
        
      

     
      

        
        
        
      

       .     ,            .  .       ,             (   ),         . 
      

        
        
        
      

         .       getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     class Student implements Person, Naming { ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

           getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Naming
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      ,  Java        .    getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Student
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .           ,   : 
      

        
        
        
      

     class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,  Naming
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
            getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     interface Naming { String getFirstName(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        Student
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
           Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ?     ,   Java     .    ,    .       ,    ,     . 
      

        
        
        
      

     
      

        
        
        
      

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      : 
      

        
        
        
      

     class Student extends Person implements Naming { ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

            ,          .    Student
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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         getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      .   « »  .  « »    Java 7.        ,       ,    ,     .    :        ,       Object
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     .      ,        Object.toString
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Object.equals
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

      
      

        
        
        
      

          -        , -   Java, - ,   .   ?    Java ,           .    , ,    ,         . ,      ,      Java 8.
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     

Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



, - , - Java. , , , (String, String) -> int



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Java API java.util.function. , BiFunction <T, U, R>



, U R. :

BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());





, . Arrays.sort



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. , . Java . , Comparator



, , . Java 8 . - - , , .



java.util.function Java 8 API , , , . , - , API, . , @FunctionalInterface



. . , . Javadoc , . . , , . @FunctionalInterface



- .



, , checked . - checked , . , :

Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





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Callable



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).





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button.setOnAction(event -> System.out.println(event));





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button.setOnAction(System.out::println);





System.out::println



, - x -> System.out.println(x)



.



, , . :

Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



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x -> System.out.println(x)



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(x, y) -> Math.pow(x, y)



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this



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class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }





Runnable



, super::speak



, speak



. ( , , EnclosingClass.this::method



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.)





, , , new



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Button



. ? . , . , , , :

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stream



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Java. T. new T[n]



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:

Object[] buttons = stream.toArray();





. , . . Button[]::new



toArray



:

Button[] buttons = stream.toArray(Button[]::new);





toArray



. .





-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



.



, , . - repeatText



. text



count



?



, , -. - :



; , ,

- , text



count



. , -, , , "Hi!" 2000. , -. ( , . , - , .)



. - , , , Java . Java - . , . Java 8 .



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public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



. -. final



; , , .



, . . matchCount



– , , .



, , . ,

List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





, matchedObjs



final



. ( final



, .) matchedObjs



ArrayList



. , . add



, .



. . .



, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



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public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }





this.toString()



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.





. , , , . , :

for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));





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strList.forEach(System.out::println);





, . Java , . Collection



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interface Naming { String getFirstName(); }





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class Student extends Person implements Naming { ... }





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• Comparator . compare



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– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



, - , - Java. , , , (String, String) -> int



, , . Java - Object



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. Java , .



Java API java.util.function. , BiFunction <T, U, R>



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, . Arrays.sort



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, , . Java 8 . - - , , .



java.util.function Java 8 API , , , . , - , API, . , @FunctionalInterface



. . , . Javadoc , . . , , . @FunctionalInterface



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Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





Runnable.run



, . , . -. , . , call



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, , . , , event



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button.setOnAction(event -> System.out.println(event));





, println



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. :

button.setOnAction(System.out::println);





System.out::println



, - x -> System.out.println(x)



.



, , . :

Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



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x -> System.out.println(x)



. , Math::pow



(x, y) -> Math.pow(x, y)



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.



, . , Math.max



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. , , Math.max



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. , :

class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }





Runnable



, super::speak



, speak



. ( , , EnclosingClass.this::method



EnclosingClass.super::method



.)





, , , new



. , Button::new



Button



. ? . , . , , , :

List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());





stream



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collect



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Button(String)



. Button



, , , , .



. , int[]::new



: . - x -> new int[x]



.



Java. T. new T[n]



, new Object[n]



. . , , . Stream



toArray



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:

Object[] buttons = stream.toArray();





. , . . Button[]::new



toArray



:

Button[] buttons = stream.toArray(Button[]::new);





toArray



. .





-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



.



, , . - repeatText



. text



count



?



, , -. - :



; , ,

- , text



count



. , -, , , "Hi!" 2000. , -. ( , . , - , .)



. - , , , Java . Java - . , . Java 8 .



, - . Java, , , . - , . , :

public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



. -. final



; , , .



, . . matchCount



– , , .



, , . ,

List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





, matchedObjs



final



. ( final



, .) matchedObjs



ArrayList



. , . add



, .



. . .



, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



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public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }





this.toString()



toString



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. this



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, this



.





. , , , . , :

for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));





. forEach



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strList.forEach(System.out::println);





, . Java , . Collection



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interface Person { long getId(); default String getFirstName() { return "Jack"; } }





: getId



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. , Person



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.



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WindowListener/WindowAdapter



. .

, , ? C++ . , Java . :



. , . . , ( ), .

. getFirstName



:

interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }





, , ?

class Student implements Person, Naming { ... }





getFirstName



, Person



Naming



. , Java . getFirstName



Student



. , :

class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }





, Naming



getFirstName



:

interface Naming { String getFirstName(); }





Student



Person



? , Java . , . , , .



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Student



:

class Student extends Person implements Naming { ... }





, . Student



getFirstName



Person



, , Naming



getFirstName



. « » . « » Java 7. , , , . : , Object



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equals



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Object.equals



.





- , - Java, - , . ? Java , . , , , . , , Java 8.




  
  
  
  
• Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



, - , - Java. , , , (String, String) -> int



, , . Java - Object



, Object



. Java , .



Java API java.util.function. , BiFunction <T, U, R>



, U R. :

BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());





, . Arrays.sort



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. , . Java . , Comparator



, , . Java 8 . - - , , .



java.util.function Java 8 API , , , . , - , API, . , @FunctionalInterface



. . , . Javadoc , . . , , . @FunctionalInterface



- .



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Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





Runnable.run



, . , . -. , . , call



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).





, , . , , event



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button.setOnAction(event -> System.out.println(event));





, println



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. :

button.setOnAction(System.out::println);





System.out::println



, - x -> System.out.println(x)



.



, , . :

Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



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x -> System.out.println(x)



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(x, y) -> Math.pow(x, y)



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- , (x, y) -> x.compareToIgnoreCase(y)



.



, . , Math.max



, int



double



. , , Math.max



. , -, . .



this



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this



. , :

class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }





Runnable



, super::speak



, speak



. ( , , EnclosingClass.this::method



EnclosingClass.super::method



.)





, , , new



. , Button::new



Button



. ? . , . , , , :

List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());





stream



, map



collect



. , , map



Button(String)



. Button



, , , , .



. , int[]::new



: . - x -> new int[x]



.



Java. T. new T[n]



, new Object[n]



. . , , . Stream



toArray



, Object



:

Object[] buttons = stream.toArray();





. , . . Button[]::new



toArray



:

Button[] buttons = stream.toArray(Button[]::new);





toArray



. .





-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



.



, , . - repeatText



. text



count



?



, , -. - :



; , ,

- , text



count



. , -, , , "Hi!" 2000. , -. ( , . , - , .)



. - , , , Java . Java - . , . Java 8 .



, - . Java, , , . - , . , :

public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



. -. final



; , , .



, . . matchCount



– , , .



, , . ,

List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





, matchedObjs



final



. ( final



, .) matchedObjs



ArrayList



. , . add



, .



. . .



, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



- this



, . , ,

public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }





this.toString()



toString



Application



, Runnable



. this



-. - doWork



, this



.





. , , , . , :

for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));





. forEach



, .

strList.forEach(System.out::println);





, . Java , . Collection



, forEach



, , , Collection



, , . Java.



Java , ( ). . . Java 8 forEach



Iterable



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, , .



:

interface Person { long getId(); default String getFirstName() { return "Jack"; } }





: getId



, , getFirstName



. , Person



, , , getId



, , getFirstName



.



, , , Collection/AbstractCollection



WindowListener/WindowAdapter



. .

, , ? C++ . , Java . :



. , . . , ( ), .

. getFirstName



:

interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }





, , ?

class Student implements Person, Naming { ... }





getFirstName



, Person



Naming



. , Java . getFirstName



Student



. , :

class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }





, Naming



getFirstName



:

interface Naming { String getFirstName(); }





Student



Person



? , Java . , . , , .



, -Java 8 . : . .



. , , . , , Person



Student



:

class Student extends Person implements Naming { ... }





, . Student



getFirstName



Person



, , Naming



getFirstName



. « » . « » Java 7. , , , . : , Object



. , toString



equals



, , List



. , Object.toString



Object.equals



.





- , - Java, - , . ? Java , . , , , . , , Java 8.




  
  
  
  
• Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



, - , - Java. , , , (String, String) -> int



, , . Java - Object



, Object



. Java , .



Java API java.util.function. , BiFunction <T, U, R>



, U R. :

BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());





, . Arrays.sort



, BiFunction



. , . Java . , Comparator



, , . Java 8 . - - , , .



java.util.function Java 8 API , , , . , - , API, . , @FunctionalInterface



. . , . Javadoc , . . , , . @FunctionalInterface



- .



, , checked . - checked , . , :

Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





Runnable.run



, . , . -. , . , call



Callable



. , Callable ( return null



).





, , . , , event



, . ,

button.setOnAction(event -> System.out.println(event));





, println



setOnAction



. :

button.setOnAction(System.out::println);





System.out::println



, - x -> System.out.println(x)



.



, , . :

Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



-, . , System.out::println



x -> System.out.println(x)



. , Math::pow



(x, y) -> Math.pow(x, y)



. . , String::compareToIgnoreCase



- , (x, y) -> x.compareToIgnoreCase(y)



.



, . , Math.max



, int



double



. , , Math.max



. , -, . .



this



. , this::equals



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. super



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this



. , :

class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }





Runnable



, super::speak



, speak



. ( , , EnclosingClass.this::method



EnclosingClass.super::method



.)





, , , new



. , Button::new



Button



. ? . , . , , , :

List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());





stream



, map



collect



. , , map



Button(String)



. Button



, , , , .



. , int[]::new



: . - x -> new int[x]



.



Java. T. new T[n]



, new Object[n]



. . , , . Stream



toArray



, Object



:

Object[] buttons = stream.toArray();





. , . . Button[]::new



toArray



:

Button[] buttons = stream.toArray(Button[]::new);





toArray



. .





-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



.



, , . - repeatText



. text



count



?



, , -. - :



; , ,

- , text



count



. , -, , , "Hi!" 2000. , -. ( , . , - , .)



. - , , , Java . Java - . , . Java 8 .



, - . Java, , , . - , . , :

public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



. -. final



; , , .



, . . matchCount



– , , .



, , . ,

List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





, matchedObjs



final



. ( final



, .) matchedObjs



ArrayList



. , . add



, .



. . .



, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



- this



, . , ,

public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }





this.toString()



toString



Application



, Runnable



. this



-. - doWork



, this



.





. , , , . , :

for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));





. forEach



, .

strList.forEach(System.out::println);





, . Java , . Collection



, forEach



, , , Collection



, , . Java.



Java , ( ). . . Java 8 forEach



Iterable



, Collection



, , .



:

interface Person { long getId(); default String getFirstName() { return "Jack"; } }





: getId



, , getFirstName



. , Person



, , , getId



, , getFirstName



.



, , , Collection/AbstractCollection



WindowListener/WindowAdapter



. .

, , ? C++ . , Java . :



. , . . , ( ), .

. getFirstName



:

interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }





, , ?

class Student implements Person, Naming { ... }





getFirstName



, Person



Naming



. , Java . getFirstName



Student



. , :

class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }





, Naming



getFirstName



:

interface Naming { String getFirstName(); }





Student



Person



? , Java . , . , , .



, -Java 8 . : . .



. , , . , , Person



Student



:

class Student extends Person implements Naming { ... }





, . Student



getFirstName



Person



, , Naming



getFirstName



. « » . « » Java 7. , , , . : , Object



. , toString



equals



, , List



. , Object.toString



Object.equals



.





- , - Java, - , . ? Java , . , , , . , , Java 8.




  
  
  
  

Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



, - , - Java. , , , (String, String) -> int



, , . Java - Object



, Object



. Java , .



Java API java.util.function. , BiFunction <T, U, R>



, U R. :

BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());





, . Arrays.sort



, BiFunction



. , . Java . , Comparator



, , . Java 8 . - - , , .



java.util.function Java 8 API , , , . , - , API, . , @FunctionalInterface



. . , . Javadoc , . . , , . @FunctionalInterface



- .



, , checked . - checked , . , :

Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





Runnable.run



, . , . -. , . , call



Callable



. , Callable ( return null



).





, , . , , event



, . ,

button.setOnAction(event -> System.out.println(event));





, println



setOnAction



. :

button.setOnAction(System.out::println);





System.out::println



, - x -> System.out.println(x)



.



, , . :

Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



-, . , System.out::println



x -> System.out.println(x)



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     ,      .      
      

        
        
        
      

     strList.forEach(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,       .    Java     ,   .   Collection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       ,   forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      .   « »  .  « »    Java 7.        ,       ,    ,     .    :        ,       Object
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



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button.setOnAction(event -> System.out.println(event));





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.



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object::instanceMethod Class::staticMethod Class::instanceMethod



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.



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double



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, super::speak



, speak



. ( , , EnclosingClass.this::method



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Button[] buttons = stream.toArray(Button[]::new);





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-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





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repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



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public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





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final



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int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



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 Comparator .   compare
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          -.         ,     -   ,     .     -   ,    ,  ,       . 
      

        
        
        
      

     
      

        
        
        
      

         –  ,   -  .    .    : 
      

        
        
        
      

     button.setOnAction(event -> System.out.println("The button has been clicked!"));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     Java API        java.util.function.   , BiFunction <T, U, R>
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,       U     R.           : 
      

        
        
        
      

     BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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       java.util.function    Java 8  API ,  , ,       .    ,       -   ,     API,    .  ,          @FunctionalInterface
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    .  ,          .   Javadoc    ,      .     .       ,  ,  .    @FunctionalInterface
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     -   . 
      

        
        
        
      

     
      

        
        
        
      

     , ,  checked          .   -   checked ,          . ,    : 
      

        
        
        
      

     Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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        ,    .   ,     .       -.      ,       . ,  call
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     ). 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

        ,     ,        . , ,        event
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   . ,     
      

        
        
        
      

     button.setOnAction(event -> System.out.println(event));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       ,        println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       setOnAction
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  : 
      

        
        
        
      

     button.setOnAction(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      System.out::println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        ,   - x -> System.out.println(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

        , ,         .     : 
      

        
        
        
      

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             ::        .    : 
      

        
        
        
      

     
      

        
        
        
      

     object::instanceMethod Class::staticMethod Class::instanceMethod 
      

        
        
        
      

     
      

        
        
        
      

             -,    .   , System.out::println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     .   , Math::pow
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     .         .  , String::compareToIgnoreCase
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     -    ,   (x, y) -> x.compareToIgnoreCase(y)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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                  ,     . ,     Math.max
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   int
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        double
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .     ,      ,   Math.max
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,   -,       .       . 
      

        
        
        
      

     
      

        
        
        
      

         this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        . , this::equals
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     –   ,   x -> this.equals(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    super
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  super::instanceMethod
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             .   ,   : 
      

        
        
        
      

     class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          Runnable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  super::speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ( ,            ,  EnclosingClass.this::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      EnclosingClass.super::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .) 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

         ,    ,   ,     new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . , Button::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    ?    . ,     . ,       ,       ,    : 
      

        
        
        
      

     List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       collect
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         .   ,  ,   map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Button(String)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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       ,     -  ,      -  Java.    ,    ,    ,   (String, String) -> int
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     ,  Object
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        .  Java      ,       . 
      

        
        
        
      

     
      

        
        
        
      

     Java API        java.util.function.   , BiFunction <T, U, R>
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,       U     R.           : 
      

        
        
        
      

     BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       ,      .    Arrays.sort
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   BiFunction
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .        ,     .   Java    .  ,  Comparator
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   ,          . Java 8   .     -  - ,        ,       . 
      

        
        
        
      

     
      

        
        
        
      

       java.util.function    Java 8  API ,  , ,       .    ,       -   ,     API,    .  ,          @FunctionalInterface
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    .  ,          .   Javadoc    ,      .     .       ,  ,  .    @FunctionalInterface
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     -   . 
      

        
        
        
      

     
      

        
        
        
      

     , ,  checked          .   -   checked ,          . ,    : 
      

        
        
        
      

     Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      Runnable.run
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        ,    .   ,     .       -.      ,       . ,  call
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Callable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        .  ,     Callable (  return null
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ). 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

        ,     ,        . , ,        event
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   . ,     
      

        
        
        
      

     button.setOnAction(event -> System.out.println(event));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       ,        println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       setOnAction
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  : 
      

        
        
        
      

     button.setOnAction(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      System.out::println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        ,   - x -> System.out.println(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

        , ,         .     : 
      

        
        
        
      

     Arrays.sort(strs, String::compareToIgnoreCase)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

             ::        .    : 
      

        
        
        
      

     
      

        
        
        
      

     object::instanceMethod Class::staticMethod Class::instanceMethod 
      

        
        
        
      

     
      

        
        
        
      

             -,    .   , System.out::println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      x -> System.out.println(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .   , Math::pow
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      (x, y) -> Math.pow(x, y)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .         .  , String::compareToIgnoreCase
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     -    ,   (x, y) -> x.compareToIgnoreCase(y)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

                  ,     . ,     Math.max
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   int
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        double
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .     ,      ,   Math.max
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,   -,       .       . 
      

        
        
        
      

     
      

        
        
        
      

         this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        . , this::equals
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     –   ,   x -> this.equals(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    super
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  super::instanceMethod
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             .   ,   : 
      

        
        
        
      

     class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          Runnable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  super::speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ( ,            ,  EnclosingClass.this::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      EnclosingClass.super::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .) 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

         ,    ,   ,     new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . , Button::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    ?    . ,     . ,       ,       ,    : 
      

        
        
        
      

     List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       collect
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         .   ,  ,   map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Button(String)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        .    Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,     ,     ,     . 
      

        
        
        
      

     
      

        
        
        
      

             . , int[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
           :  .   - x -> new int[x]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

             Java.      T.  new T[n]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      ,      new Object[n]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      . , ,     .  Stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   Object
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     Object[] buttons = stream.toArray();
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       .    ,   .          .  Button[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     Button[] buttons = stream.toArray(Button[]::new);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
            .      . 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

                     -.   : 
      

        
        
        
      

     public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      : 
      

        
        
        
      

     repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      text
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -.  ,       -.  ,     repeatText
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

       ,   ,   .  -      repeatText
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          .    text
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      ? 
      

        
        
        
      

     
      

        
        
        
      

      ,  ,       -. -   : 
      

        
        
        
      

     
      

        
        
        
      

           ;  , ,          
      

        
        
        
      

        -    , text
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,  -,      ,    , "Hi!"  2000.  ,      -. (   ,   . ,   -     ,           .) 
      

        
        
        
      

     
      

        
        
        
      

                .  - ,     ,  ,  Java   .  Java -  .   ,       . Java 8      . 
      

        
        
        
      

     
      

        
        
        
      

       , -       .  Java,  ,    ,   .  -     ,    . ,    : 
      

        
        
        
      

     public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         .    -  .    ,      . 
      

        
        
        
      

     int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          ,      .  matchCount++
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,     ,  ,       . 
      

        
        
        
      

     
      

        
        
        
      

             .  Java 8         final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .         -.         final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      ;  ,   ,    . 
      

        
        
        
      

     
      

        
        
        
      

      ,       .         .  matchCount
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     –        ,     ,      . 
      

        
        
        
      

     
      

        
        
        
      

      ,     ,      . , 
      

        
        
        
      

     List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,   matchedObjs
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ( final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       ,         .)    matchedObjs
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             ArrayList
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .   ,    .      add
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    . 
      

        
        
        
      

     
      

        
        
        
      

            .          .          . 
      

        
        
        
      

     
      

        
        
        
      

         ,   ,   -       .    1,  : 
      

        
        
        
      

     int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

     ,    .        ,   ,    ,     . 
      

        
        
        
      

     
      

        
        
        
      

      -     ,    .         .        ,     ,    . 
      

        
        
        
      

     Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

                 .  ,          -.     this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -     this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   . , ,   
      

        
        
        
      

     public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      this.toString()
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       toString
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Application
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    Runnable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -.   -    doWork
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             . 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

              .     ,      ,  ,  . ,  : 
      

        
        
        
      

     for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       .      forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,      .      
      

        
        
        
      

     strList.forEach(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,       .    Java     ,   .   Collection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       ,   forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   ,     ,  Collection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , ,      .     Java. 
      

        
        
        
      

     
      

        
        
        
      

      Java      ,        (    ).         .          .  Java 8  forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         Iterable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  Collection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  ,    . 
      

        
        
        
      

     
      

        
        
        
      

       : 
      

        
        
        
      

     interface Person { long getId(); default String getFirstName() { return "Jack"; } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        : getId
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   ,     getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,   Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , , ,   getId
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,   getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       . 
      

        
        
        
      

     
      

        
        
        
      

                ,         , ,  Collection/AbstractCollection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      WindowListener/WindowAdapter
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .        . 
      

        
        
        
      

      ,             ,          ?     C++      .  ,   Java  .  : 
      

        
        
        
      

     
      

        
        
        
      

       .     ,            .  .       ,             (   ),         . 
      

        
        
        
      

         .       getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,    ,  ? 
      

        
        
        
      

     class Student implements Person, Naming { ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

           getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Naming
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      ,  Java        .    getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Student
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .           ,   : 
      

        
        
        
      

     class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,  Naming
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
            getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     interface Naming { String getFirstName(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        Student
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
           Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ?     ,   Java     .    ,    .       ,    ,     . 
      

        
        
        
      

     
      

        
        
        
      

                ,     -Java 8     .      :      .       . 
      

        
        
        
      

     
      

        
        
        
      

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       getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



, - , - Java. , , , (String, String) -> int



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. Java , .



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button.setOnAction(event -> System.out.println(event));





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. :

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.



, , . :

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:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



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, super::speak



, speak



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Button[] buttons = stream.toArray(Button[]::new);





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-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

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count



text



-. , -. , repeatText



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. text



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?



, , -. - :



; , ,

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public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





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, , , .



. Java 8 final



. -. final



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– , , .



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, matchedObjs



final



. ( final



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, .



. . .



, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



- this



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 Comparator .   compare
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          -.         ,     -   ,     .     -   ,    ,  ,       . 
      

        
        
        
      

     
      

        
        
        
      

         –  ,   -  .    .    : 
      

        
        
        
      

     button.setOnAction(event -> System.out.println("The button has been clicked!"));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         . 
      

        
        
        
      

     
      

        
        
        
      

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        .  Java      ,       . 
      

        
        
        
      

     
      

        
        
        
      

     Java API        java.util.function.   , BiFunction <T, U, R>
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,       U     R.           : 
      

        
        
        
      

     BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     .    .  ,          .   Javadoc    ,      .     .       ,  ,  .    @FunctionalInterface
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     -   . 
      

        
        
        
      

     
      

        
        
        
      

     , ,  checked          .   -   checked ,          . ,    : 
      

        
        
        
      

     Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     ). 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

        ,     ,        . , ,        event
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   . ,     
      

        
        
        
      

     button.setOnAction(event -> System.out.println(event));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       ,        println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     .  : 
      

        
        
        
      

     button.setOnAction(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      System.out::println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        ,   - x -> System.out.println(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     object::instanceMethod Class::staticMethod Class::instanceMethod 
      

        
        
        
      

     
      

        
        
        
      

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     .         .  , String::compareToIgnoreCase
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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                  ,     . ,     Math.max
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   int
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        double
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .     ,      ,   Math.max
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,   -,       .       . 
      

        
        
        
      

     
      

        
        
        
      

         this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        . , this::equals
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     –   ,   x -> this.equals(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    super
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  super::instanceMethod
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             .   ,   : 
      

        
        
        
      

     class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          Runnable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  super::speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ( ,            ,  EnclosingClass.this::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      EnclosingClass.super::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .) 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

         ,    ,   ,     new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . , Button::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    ?    . ,     . ,       ,       ,    : 
      

        
        
        
      

     List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       collect
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         .   ,  ,   map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Button(String)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        .    Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,     ,     ,     . 
      

        
        
        
      

     
      

        
        
        
      

             . , int[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
           :  .   - x -> new int[x]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

             Java.      T.  new T[n]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      ,      new Object[n]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      . , ,     .  Stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   Object
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     Object[] buttons = stream.toArray();
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       .    ,   .          .  Button[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     Button[] buttons = stream.toArray(Button[]::new);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
            .      . 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

                     -.   : 
      

        
        
        
      

     public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      : 
      

        
        
        
      

     repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      text
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -.  ,       -.  ,     repeatText
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

       ,   ,   .  -      repeatText
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          .    text
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      ? 
      

        
        
        
      

     
      

        
        
        
      

      ,  ,       -. -   : 
      

        
        
        
      

     
      

        
        
        
      

           ;  , ,          
      

        
        
        
      

        -    , text
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,  -,      ,    , "Hi!"  2000.  ,      -. (   ,   . ,   -     ,           .) 
      

        
        
        
      

     
      

        
        
        
      

                .  - ,     ,  ,  Java   .  Java -  .   ,       . Java 8      . 
      

        
        
        
      

     
      

        
        
        
      

       , -       .  Java,  ,    ,   .  -     ,    . ,    : 
      

        
        
        
      

     public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         .    -  .    ,      . 
      

        
        
        
      

     int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          ,      .  matchCount++
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,     ,  ,       . 
      

        
        
        
      

     
      

        
        
        
      

             .  Java 8         final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .         -.         final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      ,   matchedObjs
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ( final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       ,         .)    matchedObjs
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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             . 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

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     strList.forEach(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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       : 
      

        
        
        
      

     interface Person { long getId(); default String getFirstName() { return "Jack"; } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        : getId
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   ,     getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     ,    ,   getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       . 
      

        
        
        
      

     
      

        
        
        
      

                ,         , ,  Collection/AbstractCollection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      ,             ,          ?     C++      .  ,   Java  .  : 
      

        
        
        
      

     
      

        
        
        
      

       .     ,            .  .       ,             (   ),         . 
      

        
        
        
      

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     : 
      

        
        
        
      

     interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     class Student implements Person, Naming { ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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      .   « »  .  « »    Java 7.        ,       ,    ,     .    :        ,       Object
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     . 
      

        
        
        
      

     
      

        
        
        
      

      
      

        
        
        
      

          -        , -   Java, - ,   .   ?    Java ,           .    , ,    ,         . ,      ,      Java 8.
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     

Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



, - , - Java. , , , (String, String) -> int



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Java API java.util.function. , BiFunction <T, U, R>



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, . Arrays.sort



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- .



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Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





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Callable



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button.setOnAction(event -> System.out.println(event));





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.



, , . :

Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



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stream



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toArray



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-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



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. - , , , Java . Java - . , . Java 8 .



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public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



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– , , .



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List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





, matchedObjs



final



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, .



. . .



, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



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. , , , . , :

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class Student implements Person, Naming { ... }





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interface Naming { String getFirstName(); }





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- , - Java, - , . ? Java , . , , , . , , Java 8.





 Comparator .   compare
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          -.         ,     -   ,     .     -   ,    ,  ,       . 
      

        
        
        
      

     
      

        
        
        
      

         –  ,   -  .    .    : 
      

        
        
        
      

     button.setOnAction(event -> System.out.println("The button has been clicked!"));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         . 
      

        
        
        
      

     
      

        
        
        
      

       ,     -  ,      -  Java.    ,    ,    ,   (String, String) -> int
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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        .  Java      ,       . 
      

        
        
        
      

     
      

        
        
        
      

     Java API        java.util.function.   , BiFunction <T, U, R>
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,       U     R.           : 
      

        
        
        
      

     BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       ,      .    Arrays.sort
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   BiFunction
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .        ,     .   Java    .  ,  Comparator
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   ,          . Java 8   .     -  - ,        ,       . 
      

        
        
        
      

     
      

        
        
        
      

       java.util.function    Java 8  API ,  , ,       .    ,       -   ,     API,    .  ,          @FunctionalInterface
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    .  ,          .   Javadoc    ,      .     .       ,  ,  .    @FunctionalInterface
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     -   . 
      

        
        
        
      

     
      

        
        
        
      

     , ,  checked          .   -   checked ,          . ,    : 
      

        
        
        
      

     Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      Runnable.run
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        ,    .   ,     .       -.      ,       . ,  call
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Callable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        .  ,     Callable (  return null
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ). 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

        ,     ,        . , ,        event
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   . ,     
      

        
        
        
      

     button.setOnAction(event -> System.out.println(event));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       ,        println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       setOnAction
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  : 
      

        
        
        
      

     button.setOnAction(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      System.out::println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        ,   - x -> System.out.println(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

        , ,         .     : 
      

        
        
        
      

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             ::        .    : 
      

        
        
        
      

     
      

        
        
        
      

     object::instanceMethod Class::staticMethod Class::instanceMethod 
      

        
        
        
      

     
      

        
        
        
      

             -,    .   , System.out::println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      x -> System.out.println(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .   , Math::pow
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      (x, y) -> Math.pow(x, y)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .         .  , String::compareToIgnoreCase
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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       : 
      

        
        
        
      

     interface Person { long getId(); default String getFirstName() { return "Jack"; } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     : 
      

        
        
        
      

     interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





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button.setOnAction(event -> System.out.println(event));





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:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



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toArray



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-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



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public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





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Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





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Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





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Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





Runnable.run



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, , . , , event



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button.setOnAction(event -> System.out.println(event));





, println



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System.out::println



, - x -> System.out.println(x)



.



, , . :

Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



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x -> System.out.println(x)



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(x, y) -> Math.pow(x, y)



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this



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Runnable



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. ( , , EnclosingClass.this::method



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, , , new



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Button



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stream



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. , , map



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Object[] buttons = stream.toArray();





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:

Button[] buttons = stream.toArray(Button[]::new);





toArray



. .





-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



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count



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, , -. - :



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count



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. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



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; , , .



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List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





, matchedObjs



final



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int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



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this.toString()



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interface Person { long getId(); default String getFirstName() { return "Jack"; } }





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interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }





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class Student implements Person, Naming { ... }





getFirstName



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class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }





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getFirstName



:

interface Naming { String getFirstName(); }





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Person



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class Student extends Person implements Naming { ... }





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getFirstName



Person



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getFirstName



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Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



, - , - Java. , , , (String, String) -> int



, , . Java - Object



, Object



. Java , .



Java API java.util.function. , BiFunction <T, U, R>



, U R. :

BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());





, . Arrays.sort



, BiFunction



. , . Java . , Comparator



, , . Java 8 . - - , , .



java.util.function Java 8 API , , , . , - , API, . , @FunctionalInterface



. . , . Javadoc , . . , , . @FunctionalInterface



- .



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Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





Runnable.run



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Callable



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button.setOnAction(event -> System.out.println(event));





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button.setOnAction(System.out::println);





System.out::println



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.



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Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



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x -> System.out.println(x)



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(x, y) -> Math.pow(x, y)



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- , (x, y) -> x.compareToIgnoreCase(y)



.



, . , Math.max



, int



double



. , , Math.max



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this



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this



. , :

class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }





Runnable



, super::speak



, speak



. ( , , EnclosingClass.this::method



EnclosingClass.super::method



.)





, , , new



. , Button::new



Button



. ? . , . , , , :

List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());





stream



, map



collect



. , , map



Button(String)



. Button



, , , , .



. , int[]::new



: . - x -> new int[x]



.



Java. T. new T[n]



, new Object[n]



. . , , . Stream



toArray



, Object



:

Object[] buttons = stream.toArray();





. , . . Button[]::new



toArray



:

Button[] buttons = stream.toArray(Button[]::new);





toArray



. .





-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



.



, , . - repeatText



. text



count



?



, , -. - :



; , ,

- , text



count



. , -, , , "Hi!" 2000. , -. ( , . , - , .)



. - , , , Java . Java - . , . Java 8 .



, - . Java, , , . - , . , :

public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



. -. final



; , , .



, . . matchCount



– , , .



, , . ,

List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





, matchedObjs



final



. ( final



, .) matchedObjs



ArrayList



. , . add



, .



. . .



, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



- this



, . , ,

public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }





this.toString()



toString



Application



, Runnable



. this



-. - doWork



, this



.





. , , , . , :

for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));





. forEach



, .

strList.forEach(System.out::println);





, . Java , . Collection



, forEach



, , , Collection



, , . Java.



Java , ( ). . . Java 8 forEach



Iterable



, Collection



, , .



:

interface Person { long getId(); default String getFirstName() { return "Jack"; } }





: getId



, , getFirstName



. , Person



, , , getId



, , getFirstName



.



, , , Collection/AbstractCollection



WindowListener/WindowAdapter



. .

, , ? C++ . , Java . :



. , . . , ( ), .

. getFirstName



:

interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }





, , ?

class Student implements Person, Naming { ... }





getFirstName



, Person



Naming



. , Java . getFirstName



Student



. , :

class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }





, Naming



getFirstName



:

interface Naming { String getFirstName(); }





Student



Person



? , Java . , . , , .



, -Java 8 . : . .



. , , . , , Person



Student



:

class Student extends Person implements Naming { ... }





, . Student



getFirstName



Person



, , Naming



getFirstName



. « » . « » Java 7. , , , . : , Object



. , toString



equals



, , List



. , Object.toString



Object.equals



.





- , - Java, - , . ? Java , . , , , . , , Java 8.





Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



, - , - Java. , , , (String, String) -> int



, , . Java - Object



, Object



. Java , .



Java API java.util.function. , BiFunction <T, U, R>



, U R. :

BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());





, . Arrays.sort



, BiFunction



. , . Java . , Comparator



, , . Java 8 . - - , , .



java.util.function Java 8 API , , , . , - , API, . , @FunctionalInterface



. . , . Javadoc , . . , , . @FunctionalInterface



- .



, , checked . - checked , . , :

Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





Runnable.run



, . , . -. , . , call



Callable



. , Callable ( return null



).





, , . , , event



, . ,

button.setOnAction(event -> System.out.println(event));





, println



setOnAction



. :

button.setOnAction(System.out::println);





System.out::println



, - x -> System.out.println(x)



.



, , . :

Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



-, . , System.out::println



x -> System.out.println(x)



. , Math::pow



(x, y) -> Math.pow(x, y)



. . , String::compareToIgnoreCase



- , (x, y) -> x.compareToIgnoreCase(y)



.



, . , Math.max



, int



double



. , , Math.max



. , -, . .



this



. , this::equals



– , x -> this.equals(x)



. super



. super::instanceMethod



this



. , :

class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }





Runnable



, super::speak



, speak



. ( , , EnclosingClass.this::method



EnclosingClass.super::method



.)





, , , new



. , Button::new



Button



. ? . , . , , , :

List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());





stream



, map



collect



. , , map



Button(String)



. Button



, , , , .



. , int[]::new



: . - x -> new int[x]



.



Java. T. new T[n]



, new Object[n]



. . , , . Stream



toArray



, Object



:

Object[] buttons = stream.toArray();





. , . . Button[]::new



toArray



:

Button[] buttons = stream.toArray(Button[]::new);





toArray



. .





-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



.



, , . - repeatText



. text



count



?



, , -. - :



; , ,

- , text



count



. , -, , , "Hi!" 2000. , -. ( , . , - , .)



. - , , , Java . Java - . , . Java 8 .



, - . Java, , , . - , . , :

public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



. -. final



; , , .



, . . matchCount



– , , .



, , . ,

List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





, matchedObjs



final



. ( final



, .) matchedObjs



ArrayList



. , . add



, .



. . .



, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



- this



, . , ,

public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }





this.toString()



toString



Application



, Runnable



. this



-. - doWork



, this



.





. , , , . , :

for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));





. forEach



, .

strList.forEach(System.out::println);





, . Java , . Collection



, forEach



, , , Collection



, , . Java.



Java , ( ). . . Java 8 forEach



Iterable



, Collection



, , .



:

interface Person { long getId(); default String getFirstName() { return "Jack"; } }





: getId



, , getFirstName



. , Person



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, , getFirstName



.



, , , Collection/AbstractCollection



WindowListener/WindowAdapter



. .

, , ? C++ . , Java . :



. , . . , ( ), .

. getFirstName



:

interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }





, , ?

class Student implements Person, Naming { ... }





getFirstName



, Person



Naming



. , Java . getFirstName



Student



. , :

class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }





, Naming



getFirstName



:

interface Naming { String getFirstName(); }





Student



Person



? , Java . , . , , .



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     BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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      Runnable.run
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     button.setOnAction(event -> System.out.println(event));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     button.setOnAction(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      System.out::println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     object::instanceMethod Class::staticMethod Class::instanceMethod 
      

        
        
        
      

     
      

        
        
        
      

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         this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        . , this::equals
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     .    super
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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             .   ,   : 
      

        
        
        
      

     class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          Runnable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  super::speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      EnclosingClass.super::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .) 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

         ,    ,   ,     new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . , Button::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    ?    . ,     . ,       ,       ,    : 
      

        
        
        
      

     List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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       Button(String)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        .    Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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             . , int[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
           :  .   - x -> new int[x]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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             Java.      T.  new T[n]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      ,      new Object[n]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      . , ,     .  Stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     ,   Object
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     Object[] buttons = stream.toArray();
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       .    ,   .          .  Button[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     Button[] buttons = stream.toArray(Button[]::new);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
            .      . 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

                     -.   : 
      

        
        
        
      

     public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      : 
      

        
        
        
      

     repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     .  ,  -,      ,    , "Hi!"  2000.  ,      -. (   ,   . ,   -     ,           .) 
      

        
        
        
      

     
      

        
        
        
      

                .  - ,     ,  ,  Java   .  Java -  .   ,       . Java 8      . 
      

        
        
        
      

     
      

        
        
        
      

       , -       .  Java,  ,    ,   .  -     ,    . ,    : 
      

        
        
        
      

     public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         .    -  .    ,      . 
      

        
        
        
      

     int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          ,      .  matchCount++
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,     ,  ,       . 
      

        
        
        
      

     
      

        
        
        
      

             .  Java 8         final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .         -.         final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      ;  ,   ,    . 
      

        
        
        
      

     
      

        
        
        
      

      ,       .         .  matchCount
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      ,     ,      . , 
      

        
        
        
      

     List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,   matchedObjs
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ( final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       ,         .)    matchedObjs
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             ArrayList
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .   ,    .      add
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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            .          .          . 
      

        
        
        
      

     
      

        
        
        
      

         ,   ,   -       .    1,  : 
      

        
        
        
      

     int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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      -     ,    .         .        ,     ,    . 
      

        
        
        
      

     Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

                 .  ,          -.     this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -     this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   . , ,   
      

        
        
        
      

     public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      this.toString()
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       toString
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Application
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    Runnable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -.   -    doWork
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             . 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

              .     ,      ,  ,  . ,  : 
      

        
        
        
      

     for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       .      forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,      .      
      

        
        
        
      

     strList.forEach(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,       .    Java     ,   .   Collection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       ,   forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   ,     ,  Collection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , ,      .     Java. 
      

        
        
        
      

     
      

        
        
        
      

      Java      ,        (    ).         .          .  Java 8  forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         Iterable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     ,  ,    . 
      

        
        
        
      

     
      

        
        
        
      

       : 
      

        
        
        
      

     interface Person { long getId(); default String getFirstName() { return "Jack"; } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        : getId
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   ,     getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,   Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , , ,   getId
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,   getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       . 
      

        
        
        
      

     
      

        
        
        
      

                ,         , ,  Collection/AbstractCollection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      WindowListener/WindowAdapter
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .        . 
      

        
        
        
      

      ,             ,          ?     C++      .  ,   Java  .  : 
      

        
        
        
      

     
      

        
        
        
      

       .     ,            .  .       ,             (   ),         . 
      

        
        
        
      

         .       getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,    ,  ? 
      

        
        
        
      

     class Student implements Person, Naming { ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

           getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Naming
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      ,  Java        .    getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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-. , - , . - , , , .



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button.setOnAction(event -> System.out.println("The button has been clicked!"));





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count



text



-. , -. , repeatText



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?



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; , ,

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public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





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, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



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     button.setOnAction(event -> System.out.println("The button has been clicked!"));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         . 
      

        
        
        
      

     
      

        
        
        
      

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     ,       U     R.           : 
      

        
        
        
      

     BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     .  : 
      

        
        
        
      

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     object::instanceMethod Class::staticMethod Class::instanceMethod 
      

        
        
        
      

     
      

        
        
        
      

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     .         .  , String::compareToIgnoreCase
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     .     ,      ,   Math.max
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,   -,       .       . 
      

        
        
        
      

     
      

        
        
        
      

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        . , this::equals
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     –   ,   x -> this.equals(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    super
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  super::instanceMethod
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             .   ,   : 
      

        
        
        
      

     class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          Runnable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  super::speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ( ,            ,  EnclosingClass.this::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      EnclosingClass.super::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .) 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

         ,    ,   ,     new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . , Button::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    ?    . ,     . ,       ,       ,    : 
      

        
        
        
      

     List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       collect
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         .   ,  ,   map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Button(String)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        .    Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,     ,     ,     . 
      

        
        
        
      

     
      

        
        
        
      

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     . 
      

        
        
        
      

     
      

        
        
        
      

             Java.      T.  new T[n]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      ,      new Object[n]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      . , ,     .  Stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   Object
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     Object[] buttons = stream.toArray();
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       .    ,   .          .  Button[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     Button[] buttons = stream.toArray(Button[]::new);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
            .      . 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

                     -.   : 
      

        
        
        
      

     public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      : 
      

        
        
        
      

     repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      text
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -.  ,       -.  ,     repeatText
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

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      count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,  -,      ,    , "Hi!"  2000.  ,      -. (   ,   . ,   -     ,           .) 
      

        
        
        
      

     
      

        
        
        
      

                .  - ,     ,  ,  Java   .  Java -  .   ,       . Java 8      . 
      

        
        
        
      

     
      

        
        
        
      

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     interface Person { long getId(); default String getFirstName() { return "Jack"; } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     : 
      

        
        
        
      

     interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





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:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



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. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





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, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



- , . . , , .

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 Comparator .   compare
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          -.         ,     -   ,     .     -   ,    ,  ,       . 
      

        
        
        
      

     
      

        
        
        
      

         –  ,   -  .    .    : 
      

        
        
        
      

     button.setOnAction(event -> System.out.println("The button has been clicked!"));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     ,       U     R.           : 
      

        
        
        
      

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     .        ,     .   Java    .  ,  Comparator
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     , ,  checked          .   -   checked ,          . ,    : 
      

        
        
        
      

     Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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        ,    .   ,     .       -.      ,       . ,  call
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     ). 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

        ,     ,        . , ,        event
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   . ,     
      

        
        
        
      

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       ,        println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       setOnAction
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  : 
      

        
        
        
      

     button.setOnAction(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      System.out::println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        ,   - x -> System.out.println(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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        , ,         .     : 
      

        
        
        
      

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     object::instanceMethod Class::staticMethod Class::instanceMethod 
      

        
        
        
      

     
      

        
        
        
      

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      x -> System.out.println(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     -    ,   (x, y) -> x.compareToIgnoreCase(y)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     .  ,   -,       .       . 
      

        
        
        
      

     
      

        
        
        
      

         this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     –   ,   x -> this.equals(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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      EnclosingClass.super::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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         ,    ,   ,     new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . , Button::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    ?    . ,     . ,       ,       ,    : 
      

        
        
        
      

     List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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       Button(String)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        .    Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     Object[] buttons = stream.toArray();
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       .    ,   .          .  Button[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     Button[] buttons = stream.toArray(Button[]::new);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
            .      . 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

                     -.   : 
      

        
        
        
      

     public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      : 
      

        
        
        
      

     repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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      text
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -.  ,       -.  ,     repeatText
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     .  ,  -,      ,    , "Hi!"  2000.  ,      -. (   ,   . ,   -     ,           .) 
      

        
        
        
      

     
      

        
        
        
      

                .  - ,     ,  ,  Java   .  Java -  .   ,       . Java 8      . 
      

        
        
        
      

     
      

        
        
        
      

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     public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         .    -  .    ,      . 
      

        
        
        
      

     int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          ,      .  matchCount++
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,     ,  ,       . 
      

        
        
        
      

     
      

        
        
        
      

             .  Java 8         final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .         -.         final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      ;  ,   ,    . 
      

        
        
        
      

     
      

        
        
        
      

      ,       .         .  matchCount
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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      ,     ,      . , 
      

        
        
        
      

     List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,   matchedObjs
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ( final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       ,         .)    matchedObjs
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             ArrayList
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .   ,    .      add
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    . 
      

        
        
        
      

     
      

        
        
        
      

            .          .          . 
      

        
        
        
      

     
      

        
        
        
      

         ,   ,   -       .    1,  : 
      

        
        
        
      

     int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

     ,    .        ,   ,    ,     . 
      

        
        
        
      

     
      

        
        
        
      

      -     ,    .         .        ,     ,    . 
      

        
        
        
      

     Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

                 .  ,          -.     this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     ,   . , ,   
      

        
        
        
      

     public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      this.toString()
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       toString
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Application
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    Runnable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -.   -    doWork
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             . 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

              .     ,      ,  ,  . ,  : 
      

        
        
        
      

     for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       .      forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,      .      
      

        
        
        
      

     strList.forEach(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,       .    Java     ,   .   Collection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       ,   forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   ,     ,  Collection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , ,      .     Java. 
      

        
        
        
      

     
      

        
        
        
      

      Java      ,        (    ).         .          .  Java 8  forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         Iterable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     ,  ,    . 
      

        
        
        
      

     
      

        
        
        
      

       : 
      

        
        
        
      

     interface Person { long getId(); default String getFirstName() { return "Jack"; } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        : getId
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   ,     getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,   Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , , ,   getId
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,   getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       . 
      

        
        
        
      

     
      

        
        
        
      

                ,         , ,  Collection/AbstractCollection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      WindowListener/WindowAdapter
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .        . 
      

        
        
        
      

      ,             ,          ?     C++      .  ,   Java  .  : 
      

        
        
        
      

     
      

        
        
        
      

       .     ,            .  .       ,             (   ),         . 
      

        
        
        
      

         .       getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,    ,  ? 
      

        
        
        
      

     class Student implements Person, Naming { ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

           getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Naming
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      ,  Java        .    getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Student
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .           ,   : 
      

        
        
        
      

     class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,  Naming
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
            getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     interface Naming { String getFirstName(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        Student
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
           Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ?     ,   Java     .    ,    .       ,    ,     . 
      

        
        
        
      

     
      

        
        
        
      

                ,     -Java 8     .      :      .       . 
      

        
        
        
      

     
      

        
        
        
      

             .   ,     ,      . , ,  Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        Student
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      : 
      

        
        
        
      

     class Student extends Person implements Naming { ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

            ,          .    Student
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,    Naming
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      .   « »  .  « »    Java 7.        ,       ,    ,     .    :        ,       Object
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ,         toString
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     ,         ,  List
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      ,        Object.toString
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Object.equals
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

      
      

        
        
        
      

          -        , -   Java, - ,   .   ?    Java ,           .    , ,    ,         . ,      ,      Java 8.
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     

Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



, - , - Java. , , , (String, String) -> int



, , . Java - Object



, Object



. Java , .



Java API java.util.function. , BiFunction <T, U, R>



, U R. :

BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());





, . Arrays.sort



, BiFunction



. , . Java . , Comparator



, , . Java 8 . - - , , .



java.util.function Java 8 API , , , . , - , API, . , @FunctionalInterface



. . , . Javadoc , . . , , . @FunctionalInterface



- .



, , checked . - checked , . , :

Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





Runnable.run



, . , . -. , . , call



Callable



. , Callable ( return null



).





, , . , , event



, . ,

button.setOnAction(event -> System.out.println(event));





, println



setOnAction



. :

button.setOnAction(System.out::println);





System.out::println



, - x -> System.out.println(x)



.



, , . :

Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



-, . , System.out::println



x -> System.out.println(x)



. , Math::pow



(x, y) -> Math.pow(x, y)



. . , String::compareToIgnoreCase



- , (x, y) -> x.compareToIgnoreCase(y)



.



, . , Math.max



, int



double



. , , Math.max



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this



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this



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class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }





Runnable



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, , , new



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stream



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Java. T. new T[n]



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Button[] buttons = stream.toArray(Button[]::new);





toArray



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-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



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, , . - repeatText



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. , -, , , "Hi!" 2000. , -. ( , . , - , .)



. - , , , Java . Java - . , . Java 8 .



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public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



. -. final



; , , .



, . . matchCount



– , , .



, , . ,

List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





, matchedObjs



final



. ( final



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. , . add



, .



. . .



, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



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public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }





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. , , , . , :

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interface Naming { String getFirstName(); }





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Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





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button.setOnAction(event -> System.out.println(event));





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Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



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class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }





Runnable



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, , , new



. , Button::new



Button



. ? . , . , , , :

List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());





stream



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. Button



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:

Button[] buttons = stream.toArray(Button[]::new);





toArray



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-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



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, , . - repeatText



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count



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, , -. - :



; , ,

- , text



count



. , -, , , "Hi!" 2000. , -. ( , . , - , .)



. - , , , Java . Java - . , . Java 8 .



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public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



. -. final



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, . . matchCount



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List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





, matchedObjs



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. . .



, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



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Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





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public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }





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. , , , . , :

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interface Person { long getId(); default String getFirstName() { return "Jack"; } }





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class Student implements Person, Naming { ... }





getFirstName



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interface Naming { String getFirstName(); }





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button.setOnAction(event -> System.out.println("The button has been clicked!"));





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Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





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button.setOnAction(event -> System.out.println(event));





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Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



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class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }





Runnable



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EnclosingClass.super::method



.)





, , , new



. , Button::new



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. ? . , . , , , :

List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());





stream



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Java. T. new T[n]



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:

Object[] buttons = stream.toArray();





. , . . Button[]::new



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:

Button[] buttons = stream.toArray(Button[]::new);





toArray



. .





-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



.



, , . - repeatText



. text



count



?



, , -. - :



; , ,

- , text



count



. , -, , , "Hi!" 2000. , -. ( , . , - , .)



. - , , , Java . Java - . , . Java 8 .



, - . Java, , , . - , . , :

public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



. -. final



; , , .



, . . matchCount



– , , .



, , . ,

List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





, matchedObjs



final



. ( final



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ArrayList



. , . add



, .



. . .



, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



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, . , ,

public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }





this.toString()



toString



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.





. , , , . , :

for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));





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strList.forEach(System.out::println);





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interface Person { long getId(); default String getFirstName() { return "Jack"; } }





: getId



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. .

, , ? C++ . , Java . :



. , . . , ( ), .

. getFirstName



:

interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }





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class Student implements Person, Naming { ... }





getFirstName



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Naming



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Student



. , :

class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }





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getFirstName



:

interface Naming { String getFirstName(); }





Student



Person



? , Java . , . , , .



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Student



:

class Student extends Person implements Naming { ... }





, . Student



getFirstName



Person



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getFirstName



. « » . « » Java 7. , , , . : , Object



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Object.equals



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- , - Java, - , . ? Java , . , , , . , , Java 8.




   
   
   
   

Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



, - , - Java. , , , (String, String) -> int



, , . Java - Object



, Object



. Java , .



Java API java.util.function. , BiFunction <T, U, R>



, U R. :

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, . Arrays.sort



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. , . Java . , Comparator



, , . Java 8 . - - , , .



java.util.function Java 8 API , , , . , - , API, . , @FunctionalInterface



. . , . Javadoc , . . , , . @FunctionalInterface



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Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





Runnable.run



, . , . -. , . , call



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).





, , . , , event



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button.setOnAction(event -> System.out.println(event));





, println



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. :

button.setOnAction(System.out::println);





System.out::println



, - x -> System.out.println(x)



.



, , . :

Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



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x -> System.out.println(x)



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(x, y) -> Math.pow(x, y)



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, . , Math.max



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double



. , , Math.max



. , -, . .



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. , :

class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }





Runnable



, super::speak



, speak



. ( , , EnclosingClass.this::method



EnclosingClass.super::method



.)





, , , new



. , Button::new



Button



. ? . , . , , , :

List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());





stream



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collect



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Button(String)



. Button



, , , , .



. , int[]::new



: . - x -> new int[x]



.



Java. T. new T[n]



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:

Object[] buttons = stream.toArray();





. , . . Button[]::new



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:

Button[] buttons = stream.toArray(Button[]::new);





toArray



. .





-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



.



, , . - repeatText



. text



count



?



, , -. - :



; , ,

- , text



count



. , -, , , "Hi!" 2000. , -. ( , . , - , .)



. - , , , Java . Java - . , . Java 8 .



, - . Java, , , . - , . , :

public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



. -. final



; , , .



, . . matchCount



– , , .



, , . ,

List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





, matchedObjs



final



. ( final



, .) matchedObjs



ArrayList



. , . add



, .



. . .



, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



- this



, . , ,

public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }





this.toString()



toString



Application



, Runnable



. this



-. - doWork



, this



.





. , , , . , :

for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));





. forEach



, .

strList.forEach(System.out::println);





, . Java , . Collection



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, , , Collection



, , . Java.



Java , ( ). . . Java 8 forEach



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, , .



:

interface Person { long getId(); default String getFirstName() { return "Jack"; } }





: getId



, , getFirstName



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, , , getId



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.



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WindowListener/WindowAdapter



. .

, , ? C++ . , Java . :



. , . . , ( ), .

. getFirstName



:

interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }





, , ?

class Student implements Person, Naming { ... }





getFirstName



, Person



Naming



. , Java . getFirstName



Student



. , :

class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }





, Naming



getFirstName



:

interface Naming { String getFirstName(); }





Student



Person



? , Java . , . , , .



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. , , . , , Person



Student



:

class Student extends Person implements Naming { ... }





, . Student



getFirstName



Person



, , Naming



getFirstName



. « » . « » Java 7. , , , . : , Object



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equals



, , List



. , Object.toString



Object.equals



.





- , - Java, - , . ? Java , . , , , . , , Java 8.





 Comparator .   compare
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          -.         ,     -   ,     .     -   ,    ,  ,       . 
      

        
        
        
      

     
      

        
        
        
      

         –  ,   -  .    .    : 
      

        
        
        
      

     button.setOnAction(event -> System.out.println("The button has been clicked!"));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     Java API        java.util.function.   , BiFunction <T, U, R>
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,       U     R.           : 
      

        
        
        
      

     BiFunction<String, String, Integer> compareFunc = (firstStr, secondStr) -> Integer.compare(firstStr.length(), secondStr.length());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       ,      .    Arrays.sort
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   BiFunction
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .        ,     .   Java    .  ,  Comparator
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   ,          . Java 8   .     -  - ,        ,       . 
      

        
        
        
      

     
      

        
        
        
      

       java.util.function    Java 8  API ,  , ,       .    ,       -   ,     API,    .  ,          @FunctionalInterface
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    .  ,          .   Javadoc    ,      .     .       ,  ,  .    @FunctionalInterface
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     -   . 
      

        
        
        
      

     
      

        
        
        
      

     , ,  checked          .   -   checked ,          . ,    : 
      

        
        
        
      

     Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      Runnable.run
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        ,    .   ,     .       -.      ,       . ,  call
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Callable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        .  ,     Callable (  return null
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ). 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

        ,     ,        . , ,        event
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   . ,     
      

        
        
        
      

     button.setOnAction(event -> System.out.println(event));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       ,        println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       setOnAction
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  : 
      

        
        
        
      

     button.setOnAction(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      System.out::println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        ,   - x -> System.out.println(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

        , ,         .     : 
      

        
        
        
      

     Arrays.sort(strs, String::compareToIgnoreCase)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

             ::        .    : 
      

        
        
        
      

     
      

        
        
        
      

     object::instanceMethod Class::staticMethod Class::instanceMethod 
      

        
        
        
      

     
      

        
        
        
      

             -,    .   , System.out::println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      x -> System.out.println(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .   , Math::pow
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      (x, y) -> Math.pow(x, y)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .         .  , String::compareToIgnoreCase
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     -    ,   (x, y) -> x.compareToIgnoreCase(y)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

                  ,     . ,     Math.max
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   int
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        double
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .     ,      ,   Math.max
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,   -,       .       . 
      

        
        
        
      

     
      

        
        
        
      

         this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        . , this::equals
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     –   ,   x -> this.equals(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    super
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  super::instanceMethod
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             .   ,   : 
      

        
        
        
      

     class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          Runnable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  super::speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ( ,            ,  EnclosingClass.this::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      EnclosingClass.super::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .) 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

         ,    ,   ,     new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . , Button::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    ?    . ,     . ,       ,       ,    : 
      

        
        
        
      

     List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       collect
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         .   ,  ,   map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Button(String)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        .    Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,     ,     ,     . 
      

        
        
        
      

     
      

        
        
        
      

             . , int[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
           :  .   - x -> new int[x]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

             Java.      T.  new T[n]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      ,      new Object[n]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      . , ,     .  Stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   Object
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     Object[] buttons = stream.toArray();
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       .    ,   .          .  Button[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     Button[] buttons = stream.toArray(Button[]::new);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
            .      . 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

                     -.   : 
      

        
        
        
      

     public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      : 
      

        
        
        
      

     repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      text
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -.  ,       -.  ,     repeatText
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

       ,   ,   .  -      repeatText
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          .    text
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      ? 
      

        
        
        
      

     
      

        
        
        
      

      ,  ,       -. -   : 
      

        
        
        
      

     
      

        
        
        
      

           ;  , ,          
      

        
        
        
      

        -    , text
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,  -,      ,    , "Hi!"  2000.  ,      -. (   ,   . ,   -     ,           .) 
      

        
        
        
      

     
      

        
        
        
      

                .  - ,     ,  ,  Java   .  Java -  .   ,       . Java 8      . 
      

        
        
        
      

     
      

        
        
        
      

       , -       .  Java,  ,    ,   .  -     ,    . ,    : 
      

        
        
        
      

     public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         .    -  .    ,      . 
      

        
        
        
      

     int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          ,      .  matchCount++
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,     ,  ,       . 
      

        
        
        
      

     
      

        
        
        
      

             .  Java 8         final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .         -.         final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      ;  ,   ,    . 
      

        
        
        
      

     
      

        
        
        
      

      ,       .         .  matchCount
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     –        ,     ,      . 
      

        
        
        
      

     
      

        
        
        
      

      ,     ,      . , 
      

        
        
        
      

     List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,   matchedObjs
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ( final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       ,         .)    matchedObjs
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             ArrayList
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .   ,    .      add
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    . 
      

        
        
        
      

     
      

        
        
        
      

            .          .          . 
      

        
        
        
      

     
      

        
        
        
      

         ,   ,   -       .    1,  : 
      

        
        
        
      

     int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

     ,    .        ,   ,    ,     . 
      

        
        
        
      

     
      

        
        
        
      

      -     ,    .         .        ,     ,    . 
      

        
        
        
      

     Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

                 .  ,          -.     this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -     this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   . , ,   
      

        
        
        
      

     public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      this.toString()
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       toString
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Application
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    Runnable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -.   -    doWork
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             . 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

              .     ,      ,  ,  . ,  : 
      

        
        
        
      

     for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       .      forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,      .      
      

        
        
        
      

     strList.forEach(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,       .    Java     ,   .   Collection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       ,   forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   ,     ,  Collection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , ,      .     Java. 
      

        
        
        
      

     
      

        
        
        
      

      Java      ,        (    ).         .          .  Java 8  forEach
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         Iterable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  Collection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  ,    . 
      

        
        
        
      

     
      

        
        
        
      

       : 
      

        
        
        
      

     interface Person { long getId(); default String getFirstName() { return "Jack"; } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        : getId
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   ,     getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,   Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , , ,   getId
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,   getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       . 
      

        
        
        
      

     
      

        
        
        
      

                ,         , ,  Collection/AbstractCollection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      WindowListener/WindowAdapter
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .        . 
      

        
        
        
      

      ,             ,          ?     C++      .  ,   Java  .  : 
      

        
        
        
      

     
      

        
        
        
      

       .     ,            .  .       ,             (   ),         . 
      

        
        
        
      

         .       getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,    ,  ? 
      

        
        
        
      

     class Student implements Person, Naming { ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

           getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      Naming
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      ,  Java        .    getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Student
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .           ,   : 
      

        
        
        
      

     class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      ,  Naming
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
            getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     interface Naming { String getFirstName(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        Student
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
           Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ?     ,   Java     .    ,    .       ,    ,     . 
      

        
        
        
      

     
      

        
        
        
      

                ,     -Java 8     .      :      .       . 
      

        
        
        
      

     
      

        
        
        
      

             .   ,     ,      . , ,  Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        Student
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      : 
      

        
        
        
      

     class Student extends Person implements Naming { ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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button.setOnAction(event -> System.out.println("The button has been clicked!"));





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count



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. - . , .

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     button.setOnAction(event -> System.out.println("The button has been clicked!"));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     object::instanceMethod Class::staticMethod Class::instanceMethod 
      

        
        
        
      

     
      

        
        
        
      

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     .  ,   -,       .       . 
      

        
        
        
      

     
      

        
        
        
      

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        . , this::equals
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     –   ,   x -> this.equals(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    super
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  super::instanceMethod
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             .   ,   : 
      

        
        
        
      

     class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          Runnable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  super::speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ( ,            ,  EnclosingClass.this::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      EnclosingClass.super::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .) 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

         ,    ,   ,     new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . , Button::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    ?    . ,     . ,       ,       ,    : 
      

        
        
        
      

     List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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         .   ,  ,   map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Button(String)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        .    Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,     ,     ,     . 
      

        
        
        
      

     
      

        
        
        
      

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      ,      new Object[n]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      . , ,     .  Stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   Object
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     Object[] buttons = stream.toArray();
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       .    ,   .          .  Button[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     Button[] buttons = stream.toArray(Button[]::new);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
            .      . 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

                     -.   : 
      

        
        
        
      

     public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      : 
      

        
        
        
      

     repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      text
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      -.  ,       -.  ,     repeatText
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

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      count
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,  -,      ,    , "Hi!"  2000.  ,      -. (   ,   . ,   -     ,           .) 
      

        
        
        
      

     
      

        
        
        
      

                .  - ,     ,  ,  Java   .  Java -  .   ,       . Java 8      . 
      

        
        
        
      

     
      

        
        
        
      

       , -       .  Java,  ,    ,   .  -     ,    . ,    : 
      

        
        
        
      

     public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         .    -  .    ,      . 
      

        
        
        
      

     int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          ,      .  matchCount++
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,     ,  ,       . 
      

        
        
        
      

     
      

        
        
        
      

             .  Java 8         final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .         -.         final
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      ;  ,   ,    . 
      

        
        
        
      

     
      

        
        
        
      

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     .  : 
      

        
        
        
      

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     interface Person { long getId(); default String getFirstName() { return "Jack"; } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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Comparator . compare



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button.setOnAction(event -> System.out.println("The button has been clicked!"));





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button.setOnAction(event -> System.out.println(event));





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object::instanceMethod Class::staticMethod Class::instanceMethod



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-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



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public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

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     interface Person { long getId(); default String getFirstName() { return "Jack"; } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     .  ,   Person
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , , ,   getId
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,   getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       . 
      

        
        
        
      

     
      

        
        
        
      

                ,         , ,  Collection/AbstractCollection
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     class Student implements Person, Naming { ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     .      ,  Java        .    getFirstName
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     .           ,   : 
      

        
        
        
      

     class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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     ?     ,   Java     .    ,    .       ,    ,     . 
      

        
        
        
      

     
      

        
        
        
      

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      .   « »  .  « »    Java 7.        ,       ,    ,     .    :        ,       Object
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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Comparator . compare



-. , - , . - , , , .



– , - . . :

button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



, - , - Java. , , , (String, String) -> int



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, Object



. Java , .



Java API java.util.function. , BiFunction <T, U, R>



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, . Arrays.sort



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. . , . Javadoc , . . , , . @FunctionalInterface



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Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException





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button.setOnAction(event -> System.out.println(event));





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. :

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System.out::println



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.



, , . :

Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



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x -> System.out.println(x)



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- , (x, y) -> x.compareToIgnoreCase(y)



.



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, int



double



. , , Math.max



. , -, . .



this



. , this::equals



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class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }





Runnable



, super::speak



, speak



. ( , , EnclosingClass.this::method



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.)





, , , new



. , Button::new



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. ? . , . , , , :

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stream



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Object[] buttons = stream.toArray();





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Button[] buttons = stream.toArray(Button[]::new);





toArray



. .





-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



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. - , , , Java . Java - . , . Java 8 .



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public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





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, , , .



. Java 8 final



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List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





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final



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, .



. . .



, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



- , . . , , .

Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



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class Student implements Person, Naming { ... }





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 Comparator .   compare
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          -.         ,     -   ,     .     -   ,    ,  ,       . 
      

        
        
        
      

     
      

        
        
        
      

         –  ,   -  .    .    : 
      

        
        
        
      

     button.setOnAction(event -> System.out.println("The button has been clicked!"));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

         . 
      

        
        
        
      

     
      

        
        
        
      

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     Java API        java.util.function.   , BiFunction <T, U, R>
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,       U     R.           : 
      

        
        
        
      

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     .    .  ,          .   Javadoc    ,      .     .       ,  ,  .    @FunctionalInterface
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     -   . 
      

        
        
        
      

     
      

        
        
        
      

     , ,  checked          .   -   checked ,          . ,    : 
      

        
        
        
      

     Runnable sleepingRunner = () -> { System.out.println("…"); Thread.sleep(1000); }; // Error: Thread.sleep can throw a checkedInterruptedException
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      Runnable.run
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        ,    .   ,     .       -.      ,       . ,  call
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     ). 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

        ,     ,        . , ,        event
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   . ,     
      

        
        
        
      

     button.setOnAction(event -> System.out.println(event));
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       ,        println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       setOnAction
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  : 
      

        
        
        
      

     button.setOnAction(System.out::println);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

      System.out::println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        ,   - x -> System.out.println(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

        , ,         .     : 
      

        
        
        
      

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             ::        .    : 
      

        
        
        
      

     
      

        
        
        
      

     object::instanceMethod Class::staticMethod Class::instanceMethod 
      

        
        
        
      

     
      

        
        
        
      

             -,    .   , System.out::println
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     .   , Math::pow
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
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     .         .  , String::compareToIgnoreCase
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     -    ,   (x, y) -> x.compareToIgnoreCase(y)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

                  ,     . ,     Math.max
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   int
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        double
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .     ,      ,   Math.max
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  ,   -,       .       . 
      

        
        
        
      

     
      

        
        
        
      

         this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        . , this::equals
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     –   ,   x -> this.equals(x)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    super
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .  super::instanceMethod
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      this
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
             .   ,   : 
      

        
        
        
      

     class Speaker { public void speak() { System.out.println("Hello, world!"); } } class ConcurrentSpeaker extends Speaker { public void speak() { Thread t = new Thread(super::speak); t.start(); } }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

          Runnable
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  super::speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,  speak
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . ( ,            ,  EnclosingClass.this::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      EnclosingClass.super::method
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .) 
      

        
        
        
      

     
      

        
        
        
      

        
      

        
        
        
      

         ,    ,   ,     new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . , Button::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
          Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .    ?    . ,     . ,       ,       ,    : 
      

        
        
        
      

     List<String> strs = ...; Stream<Button> stream = strs.stream().map(Button::new); List<Button> buttons = stream.collect(Collectors.toList());
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

        stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     , map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       collect
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
         .   ,  ,   map
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       Button(String)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
        .    Button
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,    ,     ,     ,     . 
      

        
        
        
      

     
      

        
        
        
      

             . , int[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
           :  .   - x -> new int[x]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     . 
      

        
        
        
      

     
      

        
        
        
      

             Java.      T.  new T[n]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      ,      new Object[n]
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     .      . , ,     .  Stream
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
       toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     ,   Object
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     Object[] buttons = stream.toArray();
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

       .    ,   .          .  Button[]::new
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
      toArray
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     : 
      

        
        
        
      

     Button[] buttons = stream.toArray(Button[]::new);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
     
      

        
        
        
      

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. - . , .

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Comparator . compare



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button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



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Button[] buttons = stream.toArray(Button[]::new);





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. .





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repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





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int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





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for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));





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interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }





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class Student implements Person, Naming { ... }





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class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }





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interface Naming { String getFirstName(); }





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class Student extends Person implements Naming { ... }





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getFirstName



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button.setOnAction(event -> System.out.println("The button has been clicked!"));





.



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Java API java.util.function. , BiFunction <T, U, R>



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).





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button.setOnAction(event -> System.out.println(event));





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.



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Arrays.sort(strs, String::compareToIgnoreCase)





:: . :



object::instanceMethod Class::staticMethod Class::instanceMethod



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x -> System.out.println(x)



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.



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double



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Button



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stream



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. Button



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Object[] buttons = stream.toArray();





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:

Button[] buttons = stream.toArray(Button[]::new);





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. .





-. :

public static void repeatText(String text, int count) { Runnable r = () -> { for (int i = 0; i < count; i++) { System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





:

repeatText("Hi!", 2000); // Prints Hi 2000 times in a separate thread





count



text



-. , -. , repeatText



.



, , . - repeatText



. text



count



?



, , -. - :



; , ,

- , text



count



. , -, , , "Hi!" 2000. , -. ( , . , - , .)



. - , , , Java . Java - . , . Java 8 .



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public static void repeatText(String text, int count) { Runnable r = () -> { while (count > 0) { count--; // Error: Can't mutate captured variable System.out.println(text); Thread.yield(); } }; new Thread(r).start(); }





. - . , .

int matchCount = 0; for (Path p : files) new Thread(() -> { if (p has some property) matchCount++; }).start(); // Illegal to mutate matchCount





, . matchCount++



, , , .



. Java 8 final



. -. final



; , , .



, . . matchCount



– , , .



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List<Path> matchedObjs = new ArrayList<>(); for (Path p : files) new Thread(() -> { if (p has some property) matchedObjs.add(p); }).start(); // Legal to mutate matchedObjs, but unsafe





, matchedObjs



final



. ( final



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ArrayList



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, .



. . .



, , - . 1, :

int[] counts = new int[1]; button.setOnAction(event -> counts[0]++);





, . , , , .



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Path first = Paths.get("/usr/local"); Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length()); // Error: Variable first already defined





. , -. this



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public class Application() { public void doWork() { Runnable r = () -> { ...; System.out.println(this.toString()); ... }; ... } }





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.





. , , , . , :

for (int i = 0; i < strList.size(); i++) System.out.println(strList.get(i));





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strList.forEach(System.out::println);





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interface Person { long getId(); default String getFirstName() { return "Jack"; } }





: getId



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.



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, , ? C++ . , Java . :



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interface Naming { default String getFirstName() { return getClass().getName() + "_" + hashCode(); } }





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class Student implements Person, Naming { ... }





getFirstName



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Naming



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Student



. , :

class Student implements Person, Naming { public String getFirstName() { returnPerson.super.getFirstName(); } ... }





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getFirstName



:

interface Naming { String getFirstName(); }





Student



Person



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Student



:

class Student extends Person implements Naming { ... }





, . Student



getFirstName



Person



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getFirstName



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equals



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.





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