java代码中使用多线程wait/notify18

java的wait/notify的通知机制可以用来实现线程间通信。wait表示线程的等待，调用该方法会导致线程阻塞，直至另一线程调用notify或notifyAll方法才唤醒它后继续执行。经典的生产者、消费者模式就是使用wait/notify机制得以完成。

sample 代码如下：

import java.util.concurrent.TimeUnit

public class ThreadTest {
    static final Object obj = new Object();  //对象锁
    private static boolean flag = false;

    public static void main(String[] args) throws Exception {
        Thread consume = new Thread(new Consume(), "Consume");
        Thread produce = new Thread(new Produce(), "Produce");
        consume.start();
        Thread.sleep(1000);
        produce.start();

        try {
            produce.join();
            consume.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    // 生产者线程
    static class Produce implements Runnable {
        @Override
        public void run() {
            synchronized (obj) {
                System.out.println("进入生产者线程");
                System.out.println("生产");
                try {
                    TimeUnit.MILLISECONDS.sleep(2000);  //模拟生产过程
                    flag = true;
                    obj.notify();  //通知消费者
                    TimeUnit.MILLISECONDS.sleep(1000);  //模拟其他耗时操作
                    System.out.println("退出生产者线程");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    //消费者线程
    static class Consume implements Runnable {
        @Override
        public void run() {
            synchronized (obj) {
                System.out.println("进入消费者线程");
                System.out.println("wait flag 1:" + flag);
                while (!flag) {  //判断条件是否满足，若不满足则等待
                    try {
                        System.out.println("还没生产，进入等待");
                        obj.wait();
                        System.out.println("结束等待");
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                System.out.println("wait flag 2:" + flag);
                System.out.println("消费");
                System.out.println("退出消费者线程");
            }

        }
    }
}