Java实现主线程等待子线程

本文介绍两种主线程等待子线程的实现方式，以5个子线程来说明：

1、使用Thread的join()方法，join()方法会阻塞主线程继续向下执行。

2、使用java.util.concurrent中的CountDownLatch，是一个倒数计数器。初始化时先设置一个倒数计数初始值，每调用一次countDown()方法，倒数值减一，他的await()方法会阻塞当前进程，直到倒数至0。

join方式代码如下：

package com.test.thread;import java.util.ArrayList;import java.util.List;public class MyThread extends Thread{    public MyThread(String name)    {        this.setName(name);    }    @Override    public void run()    {        System.out.println(this.getName() + " staring...");        System.out.println(this.getName() + " end...");    }    /**     * @param args     */    public static void main(String[] args)    {        System.out.println("main thread starting...");        List<MyThread> list = new ArrayList<MyThread>();        for (int i = 1; i <= 5; i++)        {            MyThread my = new MyThread("Thrad " + i);            my.start();            list.add(my);        }        try        {            for (MyThread my : list)            {                my.join();            }        }        catch (InterruptedException e)        {            e.printStackTrace();        }        System.out.println("main thread end...");    }}

运行结果如下：

main thread starting...
Thrad 2 staring...
Thrad 2 end...
Thrad 4 staring...
Thrad 4 end...
Thrad 1 staring...
Thrad 1 end...
Thrad 3 staring...
Thrad 3 end...
Thrad 5 staring...
Thrad 5 end...
main thread end...
CountDownLatch方式代码如下：

package com.test.thread;import java.util.concurrent.CountDownLatch;public class MyThread2 extends Thread{    private CountDownLatch count;    public MyThread2(CountDownLatch count, String name)    {        this.count = count;        this.setName(name);    }    @Override    public void run()    {        System.out.println(this.getName() + " staring...");        System.out.println(this.getName() + " end...");        this.count.countDown();    }    /**     * @param args     */    public static void main(String[] args)    {        System.out.println("main thread starting...");        CountDownLatch count = new CountDownLatch(5);        for (int i = 1; i <= 5; i++)        {            MyThread2 my = new MyThread2(count, "Thread " + i);            my.start();        }        try        {            count.await();        }        catch (InterruptedException e)        {            e.printStackTrace();        }        System.out.println("main thread end...");    }}

运行结果如下：

main thread starting...
Thread 2 staring...
Thread 2 end...
Thread 4 staring...
Thread 4 end...
Thread 1 staring...
Thread 1 end...
Thread 3 staring...
Thread 3 end...
Thread 5 staring...
Thread 5 end...
main thread end...