java中wait、notify和notifyAll的概念用法和例子？

wait()、notify()和notifyAll()方法
新手不必过认真研究，有兴趣的可研究

这三个方法仅在 synchronized 方法中才能被调用。

wait()方法告知被调用的线程退出监视器马克-to-win并进入等待状态，直到其他线程进入相同的监视器并调用 notify( ) 方法。

notify( ) 方法通知同一对象上某一个调用 wait( )线程。 If any threads are waiting on this object, one of them is chosen to be awakened. The choice is arbitrary and occurs at the discretion of the implementation.

notifyAll() 方法通知调用 wait() 的所有线程，竞争胜利的线程将先运行。 The awakened threads will compete in the usual manner with any other threads that might be actively competing to synchronize on this object; the awakened threads enjoy no reliable privilege or disadvantage in being the next thread to lock this object。

结论：notifyall是竞争，而notify是由具体实施的jvm决定的。



见下例：

例1.11.1-本章源码

class DishMark_to_win {
    private String food = "";
    public synchronized String eat() {
        try {
            System.out.println("需要等一会，暂时无饭");
/* 当执行下面的wait，这个线程将会暂停在这,然后当下列serve执行notify,然后这个线程将从这继续执行。*/
            wait();
            System.out.println("接到通知可以了");
        } catch (InterruptedException e) {
        }
        return food;
    }

    public synchronized void serve(String f) {
        this.food = f;
        /*下面二者都行*/
        notify();
  //    notifyAll();
        System.out.println("notify本身并不会释放同步锁，synchronized块儿完了，才会释放锁");
        try {
            Thread.sleep(9000);
        } catch (Exception e) {
        }
        System.out.println("等我歇9秒，synchronized块儿完了，你才能获得锁，再给你端上去");

    }
}

class Customer extends Thread {
    private DishMark_to_win myDishMark_to_win;

    public Customer(DishMark_to_win d) {
        this.myDishMark_to_win = d;
    }

    public void run() {
        System.out.println(myDishMark_to_win.eat());
    }
}

class Restrant extends Thread {
    private DishMark_to_win myDishMark_to_win;

    public Restrant(DishMark_to_win d) {
        this.myDishMark_to_win = d;
    }

    public void run() {
        try {
            Thread.sleep(4000);
        } catch (Exception e) {
        }
        System.out.println("歇了4秒");
        myDishMark_to_win.serve("鱼香肉丝");
    }
}

public class Test {
    public static void main(String[] args) {
        DishMark_to_win d = new DishMark_to_win();
        Customer c = new Customer(d);
        Restrant r = new Restrant(d);
        c.start();
        try {
            Thread.sleep(100);
        } catch (Exception e) {
        }
        r.start();
    }
}

运行结果是
需要等一会，暂时无饭
歇了4秒
notify本身并不会释放同步锁，synchronized块儿完了，才会释放锁
等我歇9秒，synchronized块儿完了，你才能获得锁，再给你端上去
接到通知可以了
鱼香肉丝