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);
}
public void run()
{
System.out.println(this.getName() + " staring...");
System.out.println(this.getName() + " end...");
}
/**
*/
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...");
}
}
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);
}
public void run()
{
System.out.println(this.getName() + " staring...");
System.out.println(this.getName() + " end...");
this.count.countDown();
}
/**
*/
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...