Java多线程(3)：wait()/notify()实例

下面是代码实例

1 public class WaitDemo implements Runnable { 2  3     private Object lock; 4  5     public WaitDemo(Object lock) { 6         this.lock = lock; 7     } 8  9     @Override10     public void run() {11         synchronized (lock) {12             System.out.println("Begin wait() ThreadName=" + Thread.currentThread().getName());13             try {14                 // [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。15                 lock.wait();16             } catch (InterruptedException e) {17                 e.printStackTrace();18             }19             // [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。20             System.out.println("End wait() ThreadName=" + Thread.currentThread().getName());21         }22     }23 }

1 public class NotifyDemo implements Runnable { 2  3     private Object lock; 4  5     public NotifyDemo(Object lock) { 6         this.lock = lock; 7     } 8  9     @Override10     public void run() {11         synchronized (lock) {12             System.out.println("Begin notify() ThreadName=" + Thread.currentThread().getName());13             // [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。14             lock.notify();15             try {16                 System.out.println("Sleep 3s...");17                 Thread.sleep(3000);18             } catch (InterruptedException e) {19                 e.printStackTrace();20             }21             System.out.println("End notify() ThreadName=" + Thread.currentThread().getName());22             // [STEP-3] 释放锁。23         }24     }25 }

1 // 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 2 public class DemoTest { 3  4     public static void main(String[] args) throws InterruptedException { 5         Object o = new Object(); 6         // WaitDemo 7         Thread a = new Thread(new WaitDemo(o)); 8         a.setName("WaitDemo"); 9         a.start();10         Thread.sleep(2000);11         // NotifyDemo12         Thread b = new Thread(new NotifyDemo(o));13         b.setName("NotifyDemo");14         b.start();15     }16 }