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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.


Source: https://habr.com/ru/post/J216431/

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