Java主线程等待子线程执行完毕-CountDownLatch

主线程：

 

//Main主线程
public class MainThread {

    public static void main(String[] args) throws InterruptedException {
        long startTime = System.currentTimeMillis();
        int threadNum = 5 ; //线程数
        //定义正在运行的线程数
        CountDownLatch runningThreadNum = new CountDownLatch(threadNum);
        System.out.println(Thread.currentThread().getName()+ "-start" );
        //创建多个子线程
        for ( int i = 0 ; i < threadNum; i++) {
            new SubThread(runningThreadNum).start();
        }
        //等待子线程都执行完了再执行主线程剩下的动作
        runningThreadNum.await();
        System.out.println(Thread.currentThread().getName()+ "-end" );
        long endTime = System.currentTimeMillis();
        System.out.println( "runningTime:" +(endTime-startTime));
    }

}

 

子线程：

//子线程
public class SubThread extends Thread{

    //子线程记数器,记载着运行的线程数
    private CountDownLatch runningThreadNum;

    public SubThread(CountDownLatch runningThreadNum){
        this .runningThreadNum = runningThreadNum;
    }

    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName()+ "-start" );
        System.out.println(Thread.currentThread().getName()+ "-do something" );
        System.out.println(Thread.currentThread().getName()+ "-end" );
        runningThreadNum.countDown(); //正在运行的线程数减一
    }
}