Java多线程(2)：线程加入/join()
线程加入
join()方法，等待其他线程终止。在当前线程(主线程)中调用另一个线程(子线程)的join()方法，则当前线程转入阻塞状态，直到另一个线程运行结束，当前线程再由阻塞转为就绪状态。
也就是主线程中，子线程调用了join()方法后面的代码，只有等到子线程结束了才能执行。
在很多情况下，主线程生成并起动了子线程，如果子线程里要进行大量的耗时的运算，主线程往往将于子线程之前结束。
如下例子：
1 class JoinRunnable implements Runnable { 2 @Override 3 public void run() { 4 System.out.println("Child thread start."); 5 try { 6 for (int i = 1; i <= 5; i++) { 7 System.out.println("Child thread runing [" + i + "]."); 8 Thread.sleep((int) (Math.random() * 100)); 9 }10 } catch (InterruptedException e) {11 System.out.println("Child thread interrupted.");12 }13 System.out.println("Child thread end.");14 }15 }16 17 public class JoinDemo {18 // main是主线程19 public static void main(String args[]) {20 System.out.println("Main thread start.");21 new Thread(new JoinRunnable()).start();22 System.out.println("Main thread end.");23 }24 }
执行结果：
Main thread start.Main thread end.Child thread start.Child thread runing [1].Child thread runing [2].Child thread runing [3].Child thread runing [4].Child thread runing [5].Child thread end.
如果主线程需要等待子线程执行完成之后再结束，这个时候就要用到join()方法了。
如下例子：
1 class JoinRunnable implements Runnable { 2 @Override 3 public void run() { 4 System.out.println("Child thread start."); 5 try { 6 for (int i = 1; i <= 5; i++) { 7 System.out.println("Child thread runing [" + i + "]."); 8 Thread.sleep((int) (Math.random() * 100)); 9 }10 } catch (InterruptedException e) {11 System.out.println("Child thread interrupted.");12 }13 System.out.println("Child thread end.");14 }15 }16 17 public class JoinDemo {18 // main是主线程19 public static void main(String args[]) {20 System.out.println("Main thread start.");21 Thread t = new Thread(new JoinRunnable());22 t.start();23 try {24 t.join();25 } catch (InterruptedException e) {26 e.printStackTrace();27 }28 System.out.println("Main thread end.");29 }30 }
执行结果：
Main thread start.Child thread start.Child thread runing [1].Child thread runing [2].Child thread runing [3].Child thread runing [4].Child thread runing [5].Child thread end.Main thread end.
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