Java线程join示例详解

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Java线程的join方法可用于暂停当前线程的执行直至目标线程死亡。Thread中一共有三个join的重载方法。

public final void join()：该方法将当前线程放入等待队列中，直至被它调用的线程死亡为止。如果该线程被中断，则会抛出InterruptedException异常。

public final synchronized void join(long millis)：该方法用于让当前线程进入等待状态，直至被它调用的线程死亡或是经过millis毫秒。由于线程的执行依赖于操作系统，所以该方法无法保证当前线程等待的时间和指定时间一致。

public final synchronized void join(long millis, int nanos)：该方法用于让线程暂停millis毫秒nanos纳秒。

下面的例子演示了join方法的使用。该段代码的目的是确保main线程最后结束，并且仅当第一个线程死亡才能启动第三个线程。

ThreadJoinExample.java

package com.journaldev.threads;public class ThreadJoinExample {    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) {        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());    }}

上述程序的输出结果为：

Thread started:::t1Thread started:::t2Thread ended:::t1Thread started:::t3Thread ended:::t2Thread ended:::t3All threads are dead, exiting main thread

原文地址：Java Thread Join Example with Explanation

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