CountDownLatch類位於java.util.concurrent包下，利用它可以實現類似計數器的功能。

程式碼如下：

package Thread;

import java.util.concurrent.CountDownLatch;

/**
 * 
 * @author Cshuzhuo
 * @date 2018-03-13
 */
public class MyThreadTest implements Runnable{
	
	private CountDownLatch countDownLatch;
	
	public MyThreadTest(CountDownLatch countDownLatch) {
		this.countDownLatch=countDownLatch;
	}
	public void run() {
		System.out.println(Thread.currentThread().getName()+"--子執行緒執行--");
		countDownLatch.countDown();
	}
}
 

package Thread;

import java.util.concurrent.CountDownLatch;

/**
 * 
 * @author Cshuzhuo
 * @date 2018-03-13
 */
public class CountDownLatchTest {
	
	public static void main(String[] args) throws Exception {
		CountDownLatch count = new CountDownLatch(5);
		new Thread(new MyThreadTest(count)).start();
		new Thread(new MyThreadTest(count)).start();
		new Thread(new MyThreadTest(count)).start();
		new Thread(new MyThreadTest(count)).start();
		new Thread(new MyThreadTest(count)).start();
		count.await();
		System.out.println("主執行緒執行");
	}
	
	
	
}
 

說明：呼叫await()方法的執行緒會被一直阻塞，它會等待直到count值為0才繼續執行31

countDown() 會讓count-1