Java Thread join方法用来暂停当前线程直到join操作上的线程结束。java中有三个重载的join方法：
public final void join()：此方法会把当前线程变为wait，直到执行join操作的线程结束，如果该线程在执行中被中断，则会抛出InterruptedException。
public final synchronized void join(long millis)：此方法会把当前线程变为wait，直到执行join操作的线程结束或者在执行join后等待millis的时间。因为线程调度依赖于操作系统的实现，因为这并不能保证当前线程一定会在millis时间变为RUnnable。
public final synchroinzed void join(long millis, int nanos)：此方法会把当前线程变为wait，直到执行join操作的线程结束或者在join后等待millis+nanos的时间。
下面的示例程序展示了Thread join方法的用法。在这段程序要保证main线程是最后一个完成的线程，同时保证第三个线程(third thread)在第一个线程(first thread)结束后才开始执行。
package com.journaldev.threads; public class ThreadJoinExample { public static void main(String[] args) { Thread t1 = new Thread(new MyRunnable(), "t1"); Thread t2 = new Thread(new MyRunnable(), "t2"); Thread t3 = new Thread(new MyRunnable(), "t3"); t1.start(); //start second thread after waiting for 2 seconds or if it‘s dead try { t1.join(2000); } catch (InterruptedException e) { e.printStackTrace(); } t2.start(); //start third thread only when first thread is dead try { t1.join(); } catch (InterruptedException e) { e.printStackTrace(); } t3.start(); //let all threads finish execution before finishing main thread try { t1.join(); t2.join(); t3.join(); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } System.out.println("All threads are dead, exiting main thread"); } }
class MyRunnable implements Runnable{ @Override public void run() { System.out.println("Thread started:::"+Thread.currentThread().getName()); try { Thread.sleep(4000); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("Thread ended:::"+Thread.currentThread().getName()); } }
程序输出结果如下：
Thread started:::t1
Thread ended:::t1
Thread started:::t2
Thread started:::t3
Thread ended:::t2
Thread ended:::t3
All threads are dead, exiting main thread
原文链接：http://www.journaldev.com/1024/java-thread-join-example-with-explanation
[译]Java Thread join示例与详解,布布扣,bubuko.com
原文：http://www.cnblogs.com/enjiex/p/3661551.html