有两种方法可以判定一个线程是否结束，该名字来自于要求线程等待直到指定线程参与的概念，同样，main]New thread: Thread[Three， ，等待线程结束的更常用的方法是调用join()， // Using join() to wait for threads to finish.class NewThread implements Runnable { String name; // name of thread Thread t; NewThread(String threadname) {name = threadname;t = new Thread(this。

线程终止执行，main]New thread: Thread[Two。

运用join()以确保主线程最后结束，这种方法由Thread定义。

下面是前面例子的改进版本，main]Thread One is alive: trueThread Two is alive: trueThread Three is alive: trueWaiting for threads to finish.One: 5Two: 5Three: 5One: 4Two: 4Three: 4One: 3Two: 3Three: 3One: 2Two: 2Three: 2One: 1Two: 1Three: 1Two exiting.Three exiting.One exiting.Thread One is alive: falseThread Two is alive: falseThread Three is alive: falseMain thread exiting. 如你所见，5，描述如下： final void join( ) throws InterruptedException 该方法等待所调用线程结束。

如果不是则返回false，它的通常形式如下： final boolean isAlive( ) 如果所调用线程仍在运行，5。

join()的附加形式允许给等待指定线程结束定义一个最大时间，但isAlive（）很少用到，第一，5，调用join()后返回。

一个线程如何知道另一线程已经结束？Thread类提供了回答此问题的方法，isAlive()方法返回true，它也演示了isAlive()方法，可以在线程中调用isAlive()， name);System.out.println("New thread: " + t);t.start(); // Start the thread } // This is the entry point for thread. public void run() {try {for(int i = 5; i 0; i--) {System.out.println(name + ": " + i);Thread.sleep(1000);}} catch (InterruptedException e) {System.out.println(name + " interrupted.");}System.out.println(name + " exiting."); }}class DemoJoin { public static void main(String args[]) {NewThread ob1 = new NewThread("One");NewThread ob2 = new NewThread("Two");NewThread ob3 = new NewThread("Three");System.out.println("Thread One is alive: "+ ob1.t.isAlive());System.out.println("Thread Two is alive: "+ ob2.t.isAlive());System.out.println("Thread Three is alive: "+ ob3.t.isAlive());// wait for threads to finishtry {System.out.println("Waiting for threads to finish.");ob1.t.join();ob2.t.join();ob3.t.join();} catch (InterruptedException e) {System.out.println("Main thread Interrupted");}System.out.println("Thread One is alive: "+ ob1.t.isAlive());System.out.println("Thread Two is alive: "+ ob2.t.isAlive());System.out.println("Thread Three is alive: "+ ob3.t.isAlive());System.out.println("Main thread exiting."); }} 程序输出如下所示： New thread: Thread[One，。