转自http://my.oschina.net/mingyuanwang/blog/493281?p=1
为了控制线程执行的顺序，如ThreadA->ThreadB->ThreadC->ThreadA循环执行三个线程，我们需要确定唤醒、等待的顺序。这时我们可以同时使用 Obj.wait()、Obj.notify()与synchronized(Obj)来实现这个目标。
通常情况下，wait是线程在获取对象锁后，主动释放对象锁，同时本线程休眠，直到有其它线程调用对象的notify()唤醒该线程，才能继续获取对象锁，并继续执行。而notify()则是对等待对象锁的线程的唤醒操作。但值得注意的是notify()调用后，并不是马上就释放对象锁，而是在相应的synchronized(){}语句块执行结束。释放对象锁后，JVM会在执行wait()等待对象锁的线程中随机选取一线程，赋予其对象锁，唤醒线程，继续执行。
public class ThreadSerialize { public static void main(String[] args){ ThreadA threadA = new ThreadA(); ThreadB threadB = new ThreadB(); ThreadC threadC = new ThreadC(); threadA.setThreadC(threadC); threadB.setThreadA(threadA); threadC.setThreadB(threadB); threadA.start(); threadB.start(); threadC.start(); while (true){ try { Thread.currentThread().sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } } } } class ThreadA extends Thread{ private ThreadC threadC; @Override public void run() { while (true){ synchronized (threadC){ synchronized (this){ System.out.println("I am ThreadA。。。"); this.notify(); } try { threadC.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } } } public void setThreadC(ThreadC threadC) { this.threadC = threadC; } } class ThreadB extends Thread{ private ThreadA threadA; @Override public void run() { while (true){ synchronized (threadA){ synchronized (this){ System.out.println("I am ThreadB。。。"); this.notify(); } try { threadA.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } } } public void setThreadA(ThreadA threadA) { this.threadA = threadA; } } class ThreadC extends Thread{ private ThreadB threadB; @Override public void run() { while (true){ synchronized (threadB){ synchronized (this){ System.out.println("I am ThreadC。。。"); this.notify(); } try { threadB.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } } } public void setThreadB(ThreadB threadB) { this.threadB = threadB; } }
