本文介紹兩種主線程等待子線程的實現方式，以5個子線程來說明：

1、使用Thread的join()方法，join()方法會阻塞主線程繼續向下執行。

2、使用Java.util.concurrent中的CountDownLatch，是一個倒數計數器。初始化時先設置一個倒數計數初始值，每調用一次countDown()方法，倒數值減一，他的await()方法會阻塞當前進程，直到倒數至0。

join方式代碼如下：

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 list = new ArrayList();

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...");

}

}

運行結果如下：

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方式代碼如下：

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...");

}

}

運行結果如下：

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..

轉自http://blog.csdn.net/nms312/article/details/30115055

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