Java線程等待與喚醒

class ThreadA extends Thread{

    public ThreadA(String name) {
        super(name);
    }

    public void run() {
        synchronized (this) {
            System.out.println(Thread.currentThread().getName()+" call notify()");
            notify();
        }
    }
}

public class WaitTest {

    public static void main(String[] args) {

        ThreadA t1 = new ThreadA("t1");

        synchronized(t1) {
            try {
                // 啟動“線程t1”
                System.out.println(Thread.currentThread().getName()+" start t1");
                t1.start();

                // 主線程等待t1通過notify()喚醒。
                System.out.println(Thread.currentThread().getName()+" wait()");
                t1.wait();

                System.out.println(Thread.currentThread().getName()+" continue");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

輸出結果：main start t1 -> main wait() -> t1 call notify() -> main continue

其實調用t1.start()，t1為就緒狀態，只是main方法中，t1被main線程鎖住了，t1.wait()的時候，讓當前線程等待，其實是讓main線程等待了，然後釋放了t1鎖，t1線程執行，列印t1 call notify()，然後喚醒main線程，最後結束；

這裡說一下wait()與sleep()的區別，他們的共同點都是讓線程休眠，但是wait()會釋放對象同步鎖，而sleep()不會；下麵的代碼t1結束之後才會運行t2；能夠證實這一點；

public class SleepLockTest{ 

    private static Object obj = new Object();

    public static void main(String[] args){ 
        ThreadA t1 = new ThreadA("t1"); 
        ThreadA t2 = new ThreadA("t2"); 
        t1.start(); 
        t2.start();
    } 

    static class ThreadA extends Thread{
        public ThreadA(String name){ 
            super(name); 
        } 
        public void run(){ 
            synchronized (obj) {
                try {
                    for(int i=0; i <10; i++){ 
                        System.out.printf("%s: %d\n", this.getName(), i); 
                        // i能被4整除時，休眠100毫秒
                        if (i%4 == 0)
                            Thread.sleep(100);
                    }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        } 
    } 
}