CountDownLatch犹如一个计数器，调用CountDownLatch对象的countDown()方法将计数器减一，当计数器到达0时，则所有等待者或单个等待者就开始执行，就好比：裁判一声令下，运动员同时开始奔跑，或者所有运动员都跑到了终点后裁判才可以公布结果。
案例：
public class CountdownLatchTest {
public static void main(String[] args) {
/*创建一个缓存型线程池*/
ExecutorService service = Executors.newCachedThreadPool();
/*创建一个计数器只有一个数*/
final CountDownLatch cdOrder = new CountDownLatch(1);
/*创建一个计数器，有3个计数器*/
final CountDownLatch cdAnswer = new CountDownLatch(3);
/*循环模拟3个线程*/
for (int i = 0; i < 3; i++) {
Runnable runnable = new Runnable() {
public void run() {
try {
System.out.println("线程" + Thread.currentThread().getName() + "正准备接受命令");
/*等待*/
cdOrder.await();
System.out.println("线程" + Thread.currentThread().getName() + "已接受命令");
/*休眠*/
Thread.sleep((long) (Math.random() * 10000));
System.out.println("线程" + Thread.currentThread().getName() + "回应命令处理结果");
/*计数器减一*/
cdAnswer.countDown();
} catch (Exception e) {
e.printStackTrace();
}
}
};
service.execute(runnable);
}
try {
/*休眠*/
Thread.sleep((long) (Math.random() * 10000));
System.out.println("线程" + Thread.currentThread().getName() + "即将发布命令");
/*计数器减一*/
cdOrder.countDown();
System.out.println("线程" + Thread.currentThread().getName() + "已发送命令，正在等待结果");
cdAnswer.await();
System.out.println("线程" + Thread.currentThread().getName() + "已收到所有响应结果");
} catch (Exception e) {
e.printStackTrace();
}
service.shutdown();
}
}
程序运行结果：
