Java 线程中的Join、wait、notify，sleep

1.wait和notify
这两个方法都是Object中的方法,放在一块是因为他们关系非常密切.
wait就是等待这个对象的同步锁,不过调用这个方法必须先获得这个对象的同步锁,就这一点很多人就搞晕了.
这里先解释一下这两个方法,然后给出一个小例子说明.

wait:等待对象的同步锁,需要获得该对象的同步锁才可以调用这个方法,否则后收到一个 IllegalMonitorStateException,这个是运行时异常.调用这个方法后,就放弃了这个同步锁了.如果不带参数的wait方法就只 有等别人唤醒了,如果带一个参数的
化就设置等待最长时间,过了这个时间即使没有人唤醒这个线程也不再等待了.

 

notify:唤醒在等待该对象同步锁的线程(只唤醒一个,如果有多个在等待),但是notifyAll可以唤醒所有等待的线程,注意唤醒的时在notify之前wait的线程,之后的没有效果.

 

这里举一个通俗的例子,两个人共有一个卫生间(每次只能一个人用),他们都要刷牙和方便,他们是这样约定的,轮流用,第一个人先刷牙,然后第二个人刷牙...

 

 

 

class Syn
{
        public static void main(String[] args) throws Exception
        {
            TwoPeople.ONE.start();
            TwoPeople.TWO.start();
        }
}

 

class TwoPeople extends Thread
{
    private int i=0;
    static Thread ONE=new TwoPeople(1);
    static Thread TWO=new TwoPeople(2);

 

    static Object washroom=new Object();   
    private TwoPeople(int i){this.i=i;}
    public void run(){
        synchronized(washroom){
            try{
                if(i==1){
                    brush(); //1
                  washroom.wait(); //2
                    release(); //6  
                    washroom.notify(); //7
                }
            else{
                    brush(); //3
                    washroom.notify(); //4
                    washroom.wait(); //5
                    release(); //8
            }
            }catch(InterruptedException e){e.printStackTrace();}
        }
    }
    private void brush() {
            System.out.println("People "+i+" is brushing !");
             try{Thread.sleep(2000);}catch(InterruptedException e){e.printStackTrace();}
            //延迟两秒看效果
            System.out.println("People "+i+" has burshed !");
    }
    private void release(){
            System.out.println("People "+i+" is releasing !");
            try{Thread.sleep(2000);}catch(InterruptedException e){e.printStackTrace();}
            //延迟两秒看效果
            System.out.println("People "+i+" has released !");
    }
};

 

People 1 is brushing !
People 1 has burshed !
People 2 is brushing !
People 2 has burshed !
People 1 is releasing !
People 1 has released !
People 2 is releasing !
People 2 has released !

上面的代码很简短,而且表明了执行顺序,至于join和sleep还是下次再讨论吧.