"ClassName :: new" VS "new ClassName ()" в JAVA - PullRequest
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"ClassName :: new" VS "new ClassName ()" в JAVA

0 голосов
/ 17 июня 2020

вот мой код: 

public class UserThreadFactory implements ThreadFactory {
  private final String namePrefix;
  private final AtomicInteger nextId = new AtomicInteger(1);

  public UserThreadFactory(String whatFeatureOfGroup) {
    this.namePrefix = "From User ThreadFactory's " + whatFeatureOfGroup + "-Worker-";
  }

  @Override
  public Thread newThread(@NotNull Runnable r) {
    String name = namePrefix + nextId.getAndIncrement();
    Thread thread = new Thread(null, r, name, 0, false);
    System.out.println("Thread Name：" + thread.getName() + "\n HashCode：" + r.hashCode());
    return thread;
  }

public class MyRunnableThread implements Runnable {

  public MyRunnableThread() {
    System.out.println("The constructor is called");
  }

  @Override
  public void run() {
    String name = Thread.currentThread().getName();
    try {
      Thread.sleep(100);
      System.out.println(name + hashCode());
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
  }

}

public class CreateThreadByThreadFactory {
  public static void main(String[] args) {
    UserThreadFactory factory = new UserThreadFactory("localHost");
    Thread thread;
    for (int i = 0; i < 20; i++) {
      thread = factory.newThread(new MyRunnableThread());//FIRST WAY
      thread = factory.newThread(() -> new MyRunnableThread());//SECOND WAY
      thread.start();
    }
  }
}

Когда я использую первый способ создания некоторого терада в классе CreateThreadByThreadFactory, я создал двадцать потоков, каждый со своим собственным объектом MyRunnableThread. Но когда я использую второй способ создания радов, я обнаруживаю, что хэш-код их объекта MyRunableThread одинаков во всех потоках, а конструктор MyRunnableThread вызывается только один раз. Почему? Кто-нибудь может объяснить, что случилось?

Следующий код - это печать с консоли двумя способами 

FIRST WAY：

The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-1
 HashCode：1996181658
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-2
 HashCode：806353501
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-3
 HashCode：521645586
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-4
 HashCode：1296064247
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-5
 HashCode：1637070917
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-6
 HashCode：780237624
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-7
 HashCode：205797316
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-8
 HashCode：1128032093
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-9
 HashCode：1066516207
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-10
 HashCode：443308702
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-11
 HashCode：935044096
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-12
 HashCode：396180261
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-13
 HashCode：625576447
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-14
 HashCode：1560911714
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-15
 HashCode：939047783
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-16
 HashCode：1237514926
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-17
 HashCode：548246552
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-18
 HashCode：835648992
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-19
 HashCode：1134517053
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-20
 HashCode：492228202
From User ThreadFactory's localHost-Worker-161237514926
From User ThreadFactory's localHost-Worker-17548246552
From User ThreadFactory's localHost-Worker-15939047783
From User ThreadFactory's localHost-Worker-11935044096
From User ThreadFactory's localHost-Worker-10443308702
From User ThreadFactory's localHost-Worker-91066516207
From User ThreadFactory's localHost-Worker-51637070917
From User ThreadFactory's localHost-Worker-41296064247
From User ThreadFactory's localHost-Worker-3521645586
From User ThreadFactory's localHost-Worker-20492228202
From User ThreadFactory's localHost-Worker-18835648992
From User ThreadFactory's localHost-Worker-191134517053
From User ThreadFactory's localHost-Worker-141560911714
From User ThreadFactory's localHost-Worker-6780237624
From User ThreadFactory's localHost-Worker-7205797316
From User ThreadFactory's localHost-Worker-81128032093
From User ThreadFactory's localHost-Worker-12396180261
From User ThreadFactory's localHost-Worker-13625576447
From User ThreadFactory's localHost-Worker-2806353501
From User ThreadFactory's localHost-Worker-11996181658

Process finished with exit code 0

SECOND WAY：

Thread Name：From User ThreadFactory's localHost-Worker-1
 HashCode：1996181658
Thread Name：From User ThreadFactory's localHost-Worker-2
 HashCode：1996181658
Thread Name：From User ThreadFactory's localHost-Worker-3
 HashCode：1996181658
Thread Name：From User ThreadFactory's localHost-Worker-4
 HashCode：1996181658
Thread Name：From User ThreadFactory's localHost-Worker-5
 HashCode：1996181658
Thread Name：From User ThreadFactory's localHost-Worker-6
 HashCode：1996181658
Thread Name：From User ThreadFactory's localHost-Worker-7
 HashCode：1996181658
Thread Name：From User ThreadFactory's localHost-Worker-8
 HashCode：1996181658
Thread Name：From User ThreadFactory's localHost-Worker-9
 HashCode：1996181658
The constructor is called
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-10
 HashCode：1996181658
The constructor is called
The constructor is called
The constructor is called
The constructor is called
The constructor is called
The constructor is called
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-11
 HashCode：1996181658
Thread Name：From User ThreadFactory's localHost-Worker-12
 HashCode：1996181658
The constructor is called
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-13
 HashCode：1996181658
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-14
 HashCode：1996181658
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-15
 HashCode：1996181658
Thread Name：From User ThreadFactory's localHost-Worker-16
 HashCode：1996181658
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-17
 HashCode：1996181658
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-18
 HashCode：1996181658
The constructor is called
The constructor is called
Thread Name：From User ThreadFactory's localHost-Worker-19
 HashCode：1996181658
Thread Name：From User ThreadFactory's localHost-Worker-20
 HashCode：1996181658
The constructor is called
The constructor is called
The constructor is called

Process finished with exit code 0

Ответы [ 2 ]

2 голосов
/ 17 июня 2020

Вторая строка не эквивалентна первой, это Runnable, который создает экземпляр MyRunnableThread, но не вызывает его run (), если вы не добавите «.run ()». Замените на: 

thread.start();
thread = factory.newThread(() -> new MyRunnableThread().run());// SECOND WAY

Первый создает MyRunnableThread и позволяет потоку вызывать MyRunnableThread.run (), во втором поток запускает лямбду, которая создает MyRunnableThread, и вызов MyRunnableThread.run () запускается только в том случае, если вы добавляете часть ".run ()"

1 голос
/ 17 июня 2020

Спасибо, ребята, я понял, в чем проблема. 

thread = factory.newThread(MyRunnable::new);

эквивалент 

thread = factory.newThread(() -> new MyRunnable());

эквивалент 

thread = factory.newThread(new Runnable() {
  @Override
  public void run() {
    new MyRunnable();
  }
});

Это полностью отличается от 

thread = factory.newThread(new MyRunnable());

Проблема решена.

НО, почему HashCode печати всегда один и тот же , когда я использую thread = factory.newThread(() -> new MyRunnable());? Эти три метода одинаковы? IDEA также предложила мне упростить их.

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