java - 关于 Java 线程的查询

Question

请告诉我如何打印“After wait”；如何在以下代码中通知主线程:

import java.util.*;  

public class Test {

      public static void main(String[] args) throws InterruptedException {
            ArrayList al = new ArrayList(6);
            al.add(0, "abc");
        al.add(1, "abc");
        al.add(2, "abc");
        synchronized(al){
            System.out.println("Before wait");
            al.wait();
            System.out.println("After wait");
        }       

      }

}

Answer 1

wait() 调用一直阻塞，直到有人 notify() 调用它...基本上，您需要创建一个调用 al 的新线程.notify() 当主线程在 wait() 中阻塞时。

此程序打印Before wait，暂停一秒钟，然后打印After wait。

import java.util.ArrayList;

public class Test {

    public static void main(String[] args) throws InterruptedException {

        final ArrayList al = new ArrayList(6);
        al.add(0, "abc");
        al.add(1, "abc");
        al.add(2, "abc");

        // Start a thread that notifies al after one second.
        new Thread() {
            public void run() {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                synchronized (al) {
                    al.notify();      // <-- this "releases" the wait.
                }
            }
        }.start();

        synchronized (al) {
            System.out.println("Before wait");
            al.wait();
            System.out.println("After wait");
        }
    }
}

---

这是我之前的一个回答的链接，解释了为什么 wait() 和 notify() 必须 在按住监视器的锁定。

• > Why must wait() always be in synchronized block