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

package com.study.thread.concurrent;import java.util.Random;import java.util.concurrent.CountDownLatch;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;/** * @author draem0507 * @TODO 学下countdownLatch * @version 0.1 * @create 2012 15:03:28 *  */public class CountDownLatchTest {    /**     * 
     * CountDownLatch类是一个同步计数器,构造时传入int参数,     * 
     * 
     * 该参数就是计数器的初始值，每调用一次countDown()方法，计数器减1,     * 
     * 
     * 计数器大于0 时，await()方法会阻塞程序继续执行     * 
     */    public static void main(String[] args) {        CountDownLatch countDownLatch = new CountDownLatch(3);        Worker worker1 = new Worker("小明", countDownLatch);        Worker worker2 = new Worker("小红", countDownLatch);        Worker worker3 = new Worker("小强", countDownLatch);        Boss boss = new Boss(countDownLatch);        ExecutorService service = Executors.newCachedThreadPool();        service.execute(worker1);        service.execute(worker2);        service.execute(worker3);        service.execute(boss);        service.shutdown();    }}class Worker implements Runnable {    private String name;    private CountDownLatch countDownLatch;    public void run() {        doWork();        try {            Thread.sleep((new Random().nextInt(10)) * 1000);        } catch (InterruptedException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        System.out.println(name + "-->结束干活");        countDownLatch.countDown();    }    public Worker(String name, CountDownLatch countDownLatch) {        this.name = name;        this.countDownLatch = countDownLatch;    }    private void doWork() {        System.out.println(name + "-->正在干活");    }}class Boss implements Runnable {    private CountDownLatch countDownLatch;    public Boss(CountDownLatch countDownLatch) {        this.countDownLatch = countDownLatch;    }    public void run() {        System.out.println("老板正在等待验工");        try {            countDownLatch.await();        } catch (InterruptedException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        System.out.println("工人干活都结束,老板开始验工");    }}

结果:

小明-->正在干活小红-->正在干活老板正在等待验工小强-->正在干活小强-->结束干活小明-->结束干活小红-->结束干活工人干活都结束,老板开始验工

不一定都按上述结果呈现，但是最后一句话肯定是最后执行

参考:

　　

　　http://www.iteye.com/topic/1002652