CountDownLatch 实现多线程协作

java.util.concurrent.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 InterruptedException

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
await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()));

        }

        private void doWork(){
            try {
                Thread.sleep(workTime);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }finally{
            this.latch.countDown();//工人完成工作，计数器减一
            }
        }
    }


}

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