在网上看到一个例子
public class JoinTester01 implements Runnable {
private String name;
public JoinTester01(String name) {
this.name = name;
}
public void run() {
System.out.printf("%s begins: %s
", name, new Date());
try {
TimeUnit.SECONDS.sleep(4);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.printf("%s has finished: %s
", name, new Date());
}
public static void main(String[] args) {
Thread thread1 = new Thread(new JoinTester01("One"));
Thread thread2 = new Thread(new JoinTester01("Two"));
thread1.start();
thread2.start();
/*try {
thread1.join();
thread2.join();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}*/
System.out.println("Main thread is finished");
}
}
输出结果是
Main thread is finished
OneWed Mar 01 09:04:52 UTC 2017
TwoWed Mar 01 09:04:52 UTC 2017
TwoWed Mar 01 09:04:52 UTC 2017
OneWed Mar 01 09:04:52 UTC 2017
开始不相信为什么main（）的主线程都完成了，子线程还能执行，自己试了一下发现真的是这样。
原来，主线程是一个非守护线程，所以主线程执行完了并不影响其他子线程，其他子线程依然该怎么运行就还怎么运行。主线程和子线程优先级一样但是主线程会先抢占CPU，先执行。所以就会出现这样的结果。
如果加上join代码部分，结果就会使真阳：
TwoWed Mar 01 09:10:39 UTC 2017
OneWed Mar 01 09:10:39 UTC 2017
TwoWed Mar 01 09:10:40 UTC 2017
OneWed Mar 01 09:10:40 UTC 2017
Main thread is finished
thread1.join()的意思就相当于从现在开始，thread1这个线程就接在main()线程后面执行了，只有执行完thread1线程之后才会继续主线程。