Java 8の新機能

Javaはまだ死んでいない-そして人々はこれを理解し始めている。

Java 8チュートリアルへようこそ。 この資料では、言語のすべての新機能を段階的に紹介します。 デフォルトのインターフェースメソッド、ラムダ式、メソッド参照、および繰り返し可能な注釈の使用方法を学びます。 このすべての後に、短くシンプルなコード例が続きます。 記事の最後では、スレッド、機能インターフェース、連想配列の拡張に関するAPIの最新の変更、および日付を操作するためのAPIの変更について説明します。

デフォルトのインターフェースメソッド

Java 8 , default



. , . :

interface Formula {
    double calculate(int a);

    default double sqrt(int a) {
        return Math.sqrt(a);
    }
}

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

calculate



Formula



sqrt



. , , calculate



. sqrt



.

Formula formula = new Formula() {
    @Override
    public double calculate(int a) {
        return sqrt(a * 100);
    }
};

formula.calculate(100);     // 100.0
formula.sqrt(16);                // 4.0

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

formula



. : 6 sqrt(a * 100)



. , Java 8 .

-

: .

List<String> names = Arrays.asList("peter", "anna", "mike", "xenia");

Collections.sort(names, new Comparator<String>() {
    @Override
    public int compare(String a, String b) {
        return b.compareTo(a);
    }
});

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

Collections.sort



, . .



Java 8 — -, :

Collections.sort(names, (String a, String b) -> {
    return b.compareTo(a);
});

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, . :

Collections.sort(names, (String a, String b) -> b.compareTo(a));

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

{} return



. :

Collections.sort(names, (a, b) -> b.compareTo(a));

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, . , -.

- Java? , . . - . , , .



-, . , , , @FunctionalInterface



. , , .



:

@FunctionalInterface
interface Converter<F, T> {
    T convert(F from);
}

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

Converter<String, Integer> converter = (from) -> Integer.valueOf(from);
Integer converted = converter.convert("123");
System.out.println(converted);    // 123

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, @FunctionalInterface



.

, :

Converter<String, Integer> converter = Integer::valueOf;
Integer converted = converter.convert("123");
System.out.println(converted);   // 123

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

Java 8 . ::



. . :

class Something {
    String startsWith(String s) {
        return String.valueOf(s.charAt(0));
    }
}

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

Something something = new Something();
Converter<String, String> converter = something::startsWith;
String converted = converter.convert("Java");
System.out.println(converted);    // "J"

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, . :

class Person {
    String firstName;
    String lastName;

    Person() {}

    Person(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }
}

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, :

interface PersonFactory<P extends Person> {
    P create(String firstName, String lastName);
}

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

:

PersonFactory<Person> personFactory = Person::new;
Person person = personFactory.create("Peter", "Parker");

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

Person::new



. , PersonFactory.create



.

- . , final



, .

final int num = 1;
Converter<Integer, String> stringConverter = (from) -> String.valueOf(from + num);

stringConverter.convert(2);     // 3

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, num



final



. :

int num = 1;
Converter<Integer, String> stringConverter = (from) -> String.valueOf(from + num);

stringConverter.convert(2);     // 3

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

num



. :

int num = 1;
Converter<Integer, String> stringConverter = (from) -> String.valueOf(from + num);
num = 3;

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

num



- .

, -. .

class Lambda4 {
    static int outerStaticNum;
    int outerNum;

    void testScopes() {
        Converter<Integer, String> stringConverter1 = (from) -> {
            outerNum = 23;
            return String.valueOf(from);
        };

        Converter<Integer, String> stringConverter2 = (from) -> {
            outerStaticNum = 72;
            return String.valueOf(from);
        };
    }
}

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

? Formula



sqrt



, , . -.



- . :

Formula formula = (a) -> sqrt( a * 100);

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

JDK 1.8 . , , Comparator



Runnable



. @FunctionalInterface



.



Java 8 , . Google Guava. , , .

— , , boolean. , (and



, or



, negate



).

Predicate<String> predicate = (s) -> s.length() > 0;

predicate.test("foo");              // true
predicate.negate().test("foo");     // false

Predicate<Boolean> nonNull = Objects::nonNull;
Predicate<Boolean> isNull = Objects::isNull;

Predicate<String> isEmpty = String::isEmpty;
Predicate<String> isNotEmpty = isEmpty.negate();

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

. (compose



, andThen



).

Function<String, Integer> toInteger = Integer::valueOf;
Function<String, String> backToString = toInteger.andThen(String::valueOf);

backToString.apply("123");     // "123"

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

(suppliers) . , .

Supplier<Person> personSupplier = Person::new;
personSupplier.get();   // new Person

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

(consumers) , .

Consumer<Person> greeter = (p) -> System.out.println("Hello, " + p.firstName);
greeter.accept(new Person("Luke", "Skywalker"));

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

Java. Java 8 .

Comparator<Person> comparator = (p1, p2) -> p1.firstName.compareTo(p2.firstName);

Person p1 = new Person("John", "Doe");
Person p2 = new Person("Alice", "Wonderland");

comparator.compare(p1, p2);             // > 0
comparator.reversed().compare(p1, p2);  // < 0

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

(optionals) , NullPointerException. , , , .



— , null. , , - , . , null, Java 8 .

Optional<String> optional = Optional.of("bam");

optional.isPresent();           // true
optional.get();                 // "bam"
optional.orElse("fallback");    // "bam"

optional.ifPresent((s) -> System.out.println(s.charAt(0)));     // "b"

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

java.util.Stream



, . (intermediate) (terminal). , . . , , java.util.Collection



, ( ). , .



, . :

List<String> stringCollection = new ArrayList<>();
stringCollection.add("ddd2");
stringCollection.add("aaa2");
stringCollection.add("bbb1");
stringCollection.add("aaa1");
stringCollection.add("bbb3");
stringCollection.add("ccc");
stringCollection.add("bbb2");
stringCollection.add("ddd1");

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

Java 8 , Collection.stream()



Collection.parallelStream()



. .

Filter

Filter , . , .. (, forEach



) . ForEach , ( ) . ForEach . , .

stringCollection
    .stream()
    .filter((s) -> s.startsWith("a"))
    .forEach(System.out::println);

// "aaa2", "aaa1"

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

Sorted

Sorted , . , :

stringCollection
    .stream()
    .sorted()
    .filter((s) -> s.startsWith("a"))
    .forEach(System.out::println);

// "aaa1", "aaa2"

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, sorted



. stringCollection



:

System.out.println(stringCollection);
// ddd2, aaa2, bbb1, aaa1, bbb3, ccc, bbb2, ddd1

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

Map

map



. . map



. , map



.

stringCollection
    .stream()
    .map(String::toUpperCase)
    .sorted((a, b) -> b.compareTo(a))
    .forEach(System.out::println);

// "DDD2", "DDD1", "CCC", "BBB3", "BBB2", "AAA2", "AAA1"

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

Match

, , (match). boolean.

boolean anyStartsWithA = 
    stringCollection
        .stream()
        .anyMatch((s) -> s.startsWith("a"));

System.out.println(anyStartsWithA);      // true

boolean allStartsWithA = 
    stringCollection
        .stream()
        .allMatch((s) -> s.startsWith("a"));

System.out.println(allStartsWithA);      // false

boolean noneStartsWithZ = 
    stringCollection
        .stream()
        .noneMatch((s) -> s.startsWith("z"));

System.out.println(noneStartsWithZ);      // true

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

Count

Count



. long



.

long startsWithB = 
    stringCollection
        .stream()
        .filter((s) -> s.startsWith("b"))
        .count();

System.out.println(startsWithB);    // 3

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

Reduce

. .

Optional<String> reduced =
    stringCollection
        .stream()
        .sorted()
        .reduce((s1, s2) -> s1 + "#" + s2);

reduced.ifPresent(System.out::println);
// "aaa1#aaa2#bbb1#bbb2#bbb3#ccc#ddd1#ddd2"

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, . , — .



, , .



:

int max = 1000000;
List<String> values = new ArrayList<>(max);
for (int i = 0; i < max; i++) {
    UUID uuid = UUID.randomUUID();
    values.add(uuid.toString());
}

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

.

long t0 = System.nanoTime();

long count = values.stream().sorted().count();
System.out.println(count);

long t1 = System.nanoTime();

long millis = TimeUnit.NANOSECONDS.toMillis(t1 - t0);
System.out.println(String.format("sequential sort took: %d ms", millis));

// sequential sort took: 899 ms

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

long t0 = System.nanoTime();

long count = values.parallelStream().sorted().count();
System.out.println(count);

long t1 = System.nanoTime();

long millis = TimeUnit.NANOSECONDS.toMillis(t1 - t0);
System.out.println(String.format("parallel sort took: %d ms", millis));

// parallel sort took: 472 ms

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, , . , , stream()



parallelStream()



.

, (maps) . , .

Map<Integer, String> map = new HashMap<>();

for (int i = 0; i < 10; i++) {
    map.putIfAbsent(i, "val" + i);
}

map.forEach((id, val) -> System.out.println(val));

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

: putIfAbsent



null; forEach



, .



:

map.computeIfPresent(3, (num, val) -> val + num);
map.get(3);             // val33

map.computeIfPresent(9, (num, val) -> null);
map.containsKey(9);     // false

map.computeIfAbsent(23, num -> "val" + num);
map.containsKey(23);    // true

map.computeIfAbsent(3, num -> "bam");
map.get(3);             // val33

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, , :

map.remove(3, "val3");
map.get(3);             // val33

map.remove(3, "val33");
map.get(3);             // null

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

:

map.getOrDefault(42, "not found");  // not found

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

? :

map.merge(9, "val9", (value, newValue) -> value.concat(newValue));
map.get(9);             // val9

map.merge(9, "concat", (value, newValue) -> value.concat(newValue));
map.get(9);             // val9concat

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

Merge



-. — .

API

Java 8 API , java.time



. API Joda-Time, . API.

Clock

Clock



. System.currentTimeMillis()



. Instant



.

java.util.Date



.

Clock clock = Clock.systemDefaultZone();
long millis = clock.millis();

Instant instant = clock.instant();
Date legacyDate = Date.from(instant);   // legacy java.util.Date

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

ZoneId



. . , .

System.out.println(ZoneId.getAvailableZoneIds());
// prints all available timezone ids

ZoneId zone1 = ZoneId.of("Europe/Berlin");
ZoneId zone2 = ZoneId.of("Brazil/East");
System.out.println(zone1.getRules());
System.out.println(zone2.getRules());

// ZoneRules[currentStandardOffset=+01:00]
// ZoneRules[currentStandardOffset=-03:00]

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

LocalTime

LocalTime



, , 10pm 17:30:15. , . , .

LocalTime now1 = LocalTime.now(zone1);
LocalTime now2 = LocalTime.now(zone2);

System.out.println(now1.isBefore(now2));  // false

long hoursBetween = ChronoUnit.HOURS.between(now1, now2);
long minutesBetween = ChronoUnit.MINUTES.between(now1, now2);

System.out.println(hoursBetween);       // -3
System.out.println(minutesBetween);     // -239

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

LocalTime , , .

LocalTime late = LocalTime.of(23, 59, 59);
System.out.println(late);       // 23:59:59

DateTimeFormatter germanFormatter =
    DateTimeFormatter
        .ofLocalizedTime(FormatStyle.SHORT)
        .withLocale(Locale.GERMAN);

LocalTime leetTime = LocalTime.parse("13:37", germanFormatter);
System.out.println(leetTime);   // 13:37

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

LocalDate

LocalDate



, , 2014-03-11. LocalDate



LocalTime



. , . , .

LocalDate today = LocalDate.now();
LocalDate tomorrow = today.plus(1, ChronoUnit.DAYS);
LocalDate yesterday = tomorrow.minusDays(2);

LocalDate independenceDay = LocalDate.of(2014, Month.JULY, 4);
DayOfWeek dayOfWeek = independenceDay.getDayOfWeek();
System.out.println(dayOfWeek);    // FRIDAY

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

LocalDate



:

DateTimeFormatter germanFormatter =
    DateTimeFormatter
        .ofLocalizedDate(FormatStyle.MEDIUM)
        .withLocale(Locale.GERMAN);

LocalDate xmas = LocalDate.parse("24.12.2014", germanFormatter);
System.out.println(xmas);   // 2014-12-24

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

LocalDateTime

LocalDateTime



. LocalDateTime



LocalTime



LocalDate



. -:

LocalDateTime sylvester = LocalDateTime.of(2014, Month.DECEMBER, 31, 23, 59, 59);

DayOfWeek dayOfWeek = sylvester.getDayOfWeek();
System.out.println(dayOfWeek);      // WEDNESDAY

Month month = sylvester.getMonth();
System.out.println(month);          // DECEMBER

long minuteOfDay = sylvester.getLong(ChronoField.MINUTE_OF_DAY);
System.out.println(minuteOfDay);    // 1439

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

Instant



.

Instant instant = sylvester
        .atZone(ZoneId.systemDefault())
        .toInstant();

Date legacyDate = Date.from(instant);
System.out.println(legacyDate);     // Wed Dec 31 23:59:59 CET 2014

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

- , . .

DateTimeFormatter formatter =
    DateTimeFormatter
        .ofPattern("MMM dd, yyyy - HH:mm");

LocalDateTime parsed = LocalDateTime.parse("Nov 03, 2014 - 07:13", formatter);
String string = formatter.format(parsed);
System.out.println(string);     // Nov 03, 2014 - 07:13

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

java.text.NumberFormat



, DateTimeFormatter



.



.

Java 8 . , , .



-, :

@interface Hints {
    Hint[] value();
}

@Repeatable(Hints.class)
@interface Hint {
    String value();
}

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

Java 8 @Repeatable



.



1: - ( )

@Hints({@Hint("hint1"), @Hint("hint2")})
class Person {}

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

2: ( )

@Hint("hint1")
@Hint("hint2")
class Person {}

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

2 @Hints



. .

Hint hint = Person.class.getAnnotation(Hint.class);
System.out.println(hint);                   // null

Hints hints1 = Person.class.getAnnotation(Hints.class);
System.out.println(hints1.value().length);  // 2

Hint[] hints2 = Person.class.getAnnotationsByType(Hint.class);
System.out.println(hints2.length);          // 2

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

@Hints Person



, getAnnotation(Hints.class)



. getAnnotationsByType



, @Hint



.



, Java 8 :

@Target({ElementType.TYPE_PARAMETER, ElementType.TYPE_USE})
@interface MyAnnotation {}

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

Java 8 . JDK 1.8, , Arrays.parallelSort



, StampedLock



, CompletableFuture



.



GitHub.