java并发编程CountDownLatch

 /**
      * CountDownLatch用法
      * CountDownLatch类位于java.util.concurrent包下，利用它可以实现类似计数器的功能。比如有一个任务A，
      * 它要等待其他4个任务执行完毕之后才能执行，此时就可以利用CountDownLatch来实现这种功能了
      */
     @Test
     public void getThread(){
         final CountDownLatch latch = new CountDownLatch(2);
         new Thread (){
             @Override
             public void run() {
                 try {
                     System.out.println("子线程"+Thread.currentThread().getName()+"正在执行");
                     Thread.sleep(3000);
                     System.out.println("子线程"+Thread.currentThread().getName()+"执行完毕");
                     latch.countDown();
                     System.out.println(latch);
                 }catch (InterruptedException e){
                     e.printStackTrace();
                 }
             }
         }.start();
         new Thread (){
             @Override
             public void run() {
                 try {
                     System.out.println("子线程"+Thread.currentThread().getName()+"正在执行");
                     Thread.sleep(3000);
                     System.out.println("子线程"+Thread.currentThread().getName()+"执行完毕");
                     latch.countDown();
                     System.out.println(latch);
                 }catch (InterruptedException e){
                     e.printStackTrace();
                 }
             }
         }.start();

         try {
             System.out.println("等待2个子线程执行完毕...");
             latch.await();
             System.out.println("2个子线程已经执行完毕");
             System.out.println("继续执行主线程");
         }catch(InterruptedException e){
             e.printStackTrace();
         }
     }