方法二CountDownLatch
CountDownLatch是一个同步辅助类,用来判断多线程是否执行完成。
它的原理是首先声明一共运行多少个线程任务，然后每完成一个线程任务，计数器就减一，当计数器等于0，说明所有的多线程都运行完成了。
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。
使用方法
如果你确定了你开启的线程数。
那么在主程序运行前。
CountDownLatch countdown = new CountDownLatch(10);//这里的10就是你的子线程数。
在每个子线程结束后，调用 countdown.countDown();
在主线程里启动子线程的方法后面添加。
countdown.await();//这里进行同步等待
等所有子线程结束后，执行 countdown.await()后面的代码。
使用例子
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();
}
}
}
}
输出结果
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 |
