CountDownLatch，一个同步辅助类，在完成一组正在其他线程中执行的操作之前，它允许一个或多个线程一直等待。

主要方法

 public CountDownLatch(int count);

 public void countDown();

 public void await() throws 

 

构造方法参数指定了计数的次数

countDown方法，当前线程调用此方法，则计数减一

awaint方法，调用此方法会一直阻塞当前线程，直到计时器的值为0

public class CountDownLatchDemo {final static SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");    public static void main(String[] args) throws InterruptedException {    CountDownLatch latch=new CountDownLatch(2);//两个工人的协作    Worker worker1=new Worker("zhang san", 5000, latch);    Worker worker2=new Worker("li si", 8000, latch);    worker1.start();//    worker2.start();//    latch.await();//等待所有工人完成工作        System.out.println("all work done at "+sdf.format(new Date()));}            static class Worker extends Thread{    String workerName;     int workTime;    CountDownLatch latch;    public Worker(String workerName ,int workTime ,CountDownLatch latch){     this.workerName=workerName;     this.workTime=workTime;     this.latch=latch;    }    public void run(){    System.out.println("Worker "+workerName+" do work begin at "+sdf.format(new Date()));    doWork();//工作了    System.out.println("Worker "+workerName+" do work complete at "+sdf.format(new Date()));    latch.countDown();//工人完成工作，计数器减一    }        private void doWork(){    try {Thread.sleep(workTime);} catch (InterruptedException e) {e.printStackTrace();}    }    }    }

输出：

Worker zhang san do work begin at 2011-04-14 11:05:11

Worker li si do work begin at 2011-04-14 11:05:11Worker zhang san do work complete at 2011-04-14 11:05:16Worker li si do work complete at 2011-04-14 11:05:19all work done at 2011-04-14 11:05:19