java - 等待和通知 - 打印不同的线程 ID

Question

抱歉，如果这是一个基本问题。我是线程新手。我试图理解 wait() 和 notification() 线程。问题是当我在同一个类上等待和通知时，线程 ID 的打印方式不同。是的，通知正常发生，但我想知道为什么通知线程 ID 不断变化？请阐明一下，等待和通知应该发生在同一个线程中，不是吗？

等待线程:

import java.util.concurrent.CompletableFuture;

public class ThreadWait implements Runnable {

    private static ThreadWait threadWait;
    private ThreadNotify threadNotify = ThreadNotify.getInstance();

    private ThreadWait() {
    }

    public static ThreadWait getInstance() {
        if (threadWait == null) {
            threadWait = new ThreadWait();
        }

        return threadWait;
    }

    @Override
    public void run() {
        synchronized (this) {
            try {
                for (int i = 0; i < 5; i++) {

                    Thread.sleep(2000);

                    CompletableFuture.runAsync(() -> {
                        // method call in async.
                        threadNotify.notifyThread();
                    });


                    System.out.println(Thread.currentThread().getId() + "=======ThreadWait : wait========");
                    wait();

                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public void notifyThread() {
        synchronized (this) {
            System.out.println(Thread.currentThread().getId() + "=======ThreadWait : Notified========");
            notify();
        }
    }
}

通知线程

public class ThreadNotify {

    private static ThreadNotify threadNotify;
    private ThreadWait threadWait;

    private ThreadNotify(){}

    public static ThreadNotify getInstance(){
        if(threadNotify == null){
            threadNotify = new ThreadNotify();
        }

        return threadNotify;
    }

    public void notifyThread(){

        threadWait = ThreadWait.getInstance();
        fibonacci(44);
        //threadWait.notify()
        threadWait.notifyThread(); // want to print threadIDs, so created this method.
    }

    private int fibonacci(int n) {
        if (n <= 1)
            return n;
        else
            return fibonacci(n - 1) + fibonacci(n - 2);
    }

}

主线程:

public class MainThread {
    public static void main(String[] args) {

        ThreadWait wait = ThreadWait.getInstance();

        Thread th = new Thread(wait);
        th.start();
    }
}

输出:

12=======ThreadWait : wait========
14=======ThreadWait : Notified========
12=======ThreadWait : wait========
15=======ThreadWait : Notified========
12=======ThreadWait : wait========
16=======ThreadWait : Notified========
12=======ThreadWait : wait========
17=======ThreadWait : Notified========
12=======ThreadWait : wait========
18=======ThreadWait : Notified========

Answer 1

如果您在主类中看到代码ThreadWait wait = ThreadWait.getInstance();，您正在创建一个实例并将其交给等待线程。它使用单例模式来创建实例。但是对于通知，您使用的是 CompletableFuture 它创建了一个单独的线程