notify

 

package one;

public class NotifyTest {
    private String flag[] = { "true" };

    class NotifyThread extends Thread {
        public NotifyThread(String name) {
            super(name);
        }

        public void run() {
            try {
                sleep(3000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            synchronized (flag) {
                flag[0] = "false";
                flag.notifyAll();
                //flag.notify();
            }
        }
    };

    class WaitThread extends Thread {
        public WaitThread(String name) {
            super(name);
        }

        public void run() {
            synchronized (flag) {
                while (flag[0] != "false") {
                    System.out.println(getName() + " begin waiting!");
                    long waitTime = System.currentTimeMillis();
                    try {
                        flag.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    waitTime = System.currentTimeMillis() - waitTime;
                    System.out.println(getName() + " wait time :" + waitTime);
                }
                System.out.println(getName() + " end waiting!");
            }
        }
    }

    public static void main(String[] args) throws InterruptedException {
        System.out.println("Main Thread Run!");
        NotifyTest test = new NotifyTest();
        NotifyThread notifyThread = test.new NotifyThread("notify01");
        WaitThread waitThread01 = test.new WaitThread("waiter01");
        WaitThread waitThread02 = test.new WaitThread("waiter02");
        WaitThread waitThread03 = test.new WaitThread("waiter03");
        notifyThread.start();
        waitThread01.start();
        waitThread02.start();
        waitThread03.start();
    }

}

Main Thread Run!
waiter01 begin waiting!
waiter03 begin waiting!
waiter02 begin waiting!
waiter02 wait time :3005
waiter02 end waiting!
waiter03 wait time :3005
waiter03 end waiting!
waiter01 wait time :3005
waiter01 end waiting!

 

根据上述两点，在调用wait(), notify()或notifyAll()的时候，必须先获得锁，且状态变量须由该锁保护，而固有锁对象与固有条件队列对象又是同一个对象。也就是说，要在某个对象上执行wait，notify，先必须锁定该对象，而对应的状态变量也是由该对象锁保护的。