Java多线程(3)：wait()/notify()实例

下面是代码实例

 public class WaitDemo implements Runnable {

     private Object lock;

     public WaitDemo(Object lock) {
         this.lock = lock;
     }

     @Override
     public void run() {
         synchronized (lock) {
             System.out.println("Begin wait() ThreadName=" + Thread.currentThread().getName());
             try {
                 // [STEP-1] WaitDemo线程立刻释放获得的对象锁lock，并放弃CPU，进入等待队列。
                 lock.wait();
             } catch (InterruptedException e) {
                 e.printStackTrace();
             }
             // [STEP-4] WaitDemo有机会获得另一个线程释放的锁，并从等待的地方起开始执行。
             System.out.println("End wait() ThreadName=" + Thread.currentThread().getName());
         }
     }
 }

 public class NotifyDemo implements Runnable {

     private Object lock;

     public NotifyDemo(Object lock) {
         this.lock = lock;
     }

     @Override
     public void run() {
         synchronized (lock) {
             System.out.println("Begin notify() ThreadName=" + Thread.currentThread().getName());
             // [STEP-2] NotifyDemo线程唤醒其他挂起的线程(WaitDemo线程)。但是此时它并不立即释放锁。
             lock.notify();
             try {
                 System.out.println("Sleep 3s...");
                 Thread.sleep(3000);
             } catch (InterruptedException e) {
                 e.printStackTrace();
             }
             System.out.println("End notify() ThreadName=" + Thread.currentThread().getName());
             // [STEP-3] 释放锁。
         }
     }
 }

 // 该实例无法保证假设在线程WaitDemo和NotifyDemo的先后执行顺序。如果线程B先执行了notify()然后结束了，线程A才去执行wait()，那此时，线程A将无法被正常唤醒了
 public class DemoTest {

     public static void main(String[] args) throws InterruptedException {
         Object o = new Object();
         // WaitDemo
         Thread a = new Thread(new WaitDemo(o));
         a.setName("WaitDemo");
         a.start();
         Thread.sleep(2000);
         // NotifyDemo
         Thread b = new Thread(new NotifyDemo(o));
         b.setName("NotifyDemo");
         b.start();
     }
 }