http://blog.csdn.net/cloudeagle_bupt/article/details/21378283
转自: http://wangacidlemon.iteye.com/blog/398623
wait()方法表示,放弃当前对资源的占有权,等啊等啊,一直等到有人通知我,我才会运行后面的代码。
notify()方法表示,当前的线程已经放弃对资源的占有,
通知等待的线程来获得对资源的占有权,但是只有一个线程能够从wait状态中恢复,
然后继续运行wait()后面的语句;
notifyAll()方法表示,当前的线程已经放弃对资源的占有,
通知所有的等待线程从wait()方法后的语句开始运行。
读出什么区别没有?
上例子,先是一个nofiyAll()的例子:
- package com.thread.wait;
- public class Wait {
- private int counter = 0;
- private String name = null;
- public Wait(int counter,String name){
- this.counter = counter;
- this.name = name;
- }
- public synchronized void doSomthing(){
- int tempCounter = --counter;
- if(tempCounter <= 0){
- customizedNotifyAll();
- }
- else
- {
- while(tempCounter > 0){
- try {
- System.out.println(Thread.currentThread().getName()+"-<"+name+tempCounter+">"+"will invoke WAIT()");
- --tempCounter;
- wait();
- } catch (InterruptedException e) {
- e.printStackTrace();
- notifyAll();
- }
- System.out.println(Thread.currentThread().getName()+"-<"+name+tempCounter+">"+"has been ACTIVED");
- }
- customizedNotifyAll();
- }
- }
- public void customizedNotifyAll(){
- notifyAll();
- System.out.println(Thread.currentThread().getName()+"-<"+name+counter+">"+"::"+"INVOKED NOTIFYALL() AND FINISHED");
- }
- }
- package com.thread.wait;
- public class TestThread implements Runnable {
- private Wait wait;
- public TestThread(Wait wait){
- this.wait = wait;
- }
- public void run() {
- wait.doSomthing();
- }
- public static void main(String [] args){
- Wait wait = new Wait(4,"DAVID");
- Thread t1 = new Thread(new TestThread(wait));
- Thread t2 = new Thread(new TestThread(wait));
- Thread t3 = new Thread(new TestThread(wait));
- Thread t4 = new Thread(new TestThread(wait));
- t1.start();
- t2.start();
- t3.start();
- t4.start();
- }
- }
运行的结果:
Thread-0-<DAVID3>will invoke WAIT()
Thread-1-<DAVID2>will invoke WAIT()
Thread-2-<DAVID1>will invoke WAIT()
Thread-3-<DAVID0>::INVOKED NOTIFYALL() AND FINISHED
Thread-0-<DAVID2>has been ACTIVED
Thread-0-<DAVID2>will invoke WAIT()
Thread-1-<DAVID1>has been ACTIVED
Thread-1-<DAVID1>will invoke WAIT()
Thread-2-<DAVID0>has been ACTIVED
Thread-2-<DAVID0>::INVOKED NOTIFYALL() AND FINISHED
Thread-0-<DAVID1>has been ACTIVED
Thread-0-<DAVID1>will invoke WAIT()
Thread-1-<DAVID0>has been ACTIVED
Thread-1-<DAVID0>::INVOKED NOTIFYALL() AND FINISHED
Thread-0-<DAVID0>has been ACTIVED
Thread-0-<DAVID0>::INVOKED NOTIFYALL() AND FINISHED
看到了吧,一旦调用notifyAll()方法,所有的等待线程都会从调用wait()方法的地方继续运行起来。
这个运行结果可能每次都不一样,有时候只有两个线程运行完成而其余两个线程在等待其它线程调用notifyAll()方法,有时候只有三个线程运行完成,而另一个还在等待中。
由于本文是讲解notify以及notifyAll方法,所以对上面的原因不多加以解释。
然后是notify()方法的例子:
就是将wait类中的customizedNotifyAll()方法中的notifyAll()方法换成notify()方法
运行结果:
Thread-1-<DAVID3>will invoke WAIT()
Thread-0-<DAVID2>will invoke WAIT()
Thread-2-<DAVID1>will invoke WAIT()
Thread-3-<DAVID0>::INVOKED NOTIFYALL() AND FINISHED
Thread-1-<DAVID2>has been ACTIVED
Thread-1-<DAVID2>will invoke WAIT()
Did you see that?所有的等待线程中,只有一个线程运行完成了,而其它的线程还在傻傻地等待,poor guys!
每次运行的结果会不一样,但是始终只有一个线程能够运行完成。
Summary:
notify()方法只是让一个线程从wait中恢复过来,至于具体是哪个,那就得看那些线程的运气了(不设置优先级的情况下),继续执行后面的语句;
notifyAll()方法是让所有的线程从wait中恢复过来,继续执行后面的语句。