1、通过thread.join()方式，注意：如果有多个子线程，需要将全部的线程先start，然后再join。代码示例如下：
public class Main
{
public static void
main(String[] args)
{
long start =
System.currentTimeMillis();
List<Thread> list = new
ArrayList<Thread>();
for(int i = 0; i < 5;
i++)
{
Thread thread = new
TestThread();
thread.start();
list.add(thread);
}
try
{
for(Thread thread :
list)
{
thread.join();
}
}
catch
(InterruptedException e)
{
e.printStackTrace();
}
long end =
System.currentTimeMillis();
System.out.println("子线程执行时长：" + (end - start));
}
}
2、主线程等待多个子线程（CountDownLatch实现）
CountDownLatch，一个同步辅助类，在完成一组正在其他线程中执行的操作之前，它允许一个或多个线程一直等待。
主要方法
public CountDownLatch(int count);
public void countDown();
public void await() throws InterruptedException
构造方法参数指定了计数的次数
countDown方法，当前线程调用此方法，则计数减一
await方法，调用此方法会一直阻塞当前线程，直到计时器的值为0
示例代码如下：
public class CountDownLatchDemo { final static SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); public static void main(String[] args) throws InterruptedException { CountDownLatch latch=new CountDownLatch(2);//两个工人的协作 Worker worker1=new Worker("zhang san", 5000, latch); Worker worker2=new Worker("li si", 8000, latch); worker1.start();// worker2.start();// latch.await();//等待所有工人完成工作 System.out.println("all work done at "+sdf.format(new Date())); } static class Worker extends Thread{ String workerName; int workTime; CountDownLatch latch; public Worker(String workerName ,int workTime ,CountDownLatch latch){ this.workerName=workerName; this.workTime=workTime; this.latch=latch; } public void run(){ System.out.println("Worker "+workerName+" do work begin at "+sdf.format(new Date())); doWork();//工作了 System.out.println("Worker "+workerName+" do work complete at "+sdf.format(new Date())); latch.countDown();//工人完成工作，计数器减一 } private void doWork(){ try { Thread.sleep(workTime); } catch (InterruptedException e) { e.printStackTrace(); } } } }