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Java实现主线程等待子线程


 

  本文介绍两种主线程等待子线程的实现方式,以5个子线程来说明:

  1、使用Thread的join()方法,join()方法会阻塞主线程继续向下执行。

  2、使用java.util.concurrent中的CountDownLatch,是一个倒数计数器。初始化时先设置一个倒数计数初始值,每调用一次countDown()方法,倒数值减一,他的await()方法会阻塞当前进程,直到倒数至0.

  join方式代码如下:

  package com.test.thread;

  import java.util.ArrayList;

  import java.util.List;

  public class MyThread extends Thread

  {

  public MyThread(String name)

  {

  this.setName(name);

  }

  @Override

  public void run()

  {

  System.out.println(this.getName() + " staring…");

  System.out.println(this.getName() + " end…");

  }

  /**

  * @param args

  */

  public static void main(String[] args)

  {

  System.out.println("main thread starting…");

  List list = new ArrayList();

  for (int i = 1; i <= 5; i++)

  {

  MyThread my = new MyThread("Thrad " + i);

  my.start();

  list.add(my);

  }

  try

  {

  for (MyThread my : list)

  {

  my.join();

  }

  }

  catch (InterruptedException e)

  {

  e.printStackTrace();

  }

  System.out.println("main thread end…");

  }

  }

  运行结果如下:

  main thread starting…

  Thrad 2 staring…

  Thrad 2 end…

  Thrad 4 staring…

  Thrad 4 end…

  Thrad 1 staring…

  Thrad 1 end…

  Thrad 3 staring…

  Thrad 3 end…

  Thrad 5 staring…

  Thrad 5 end…

  main thread end…

  CountDownLatch方式代码如下:

  package com.test.thread;

  import java.util.concurrent.CountDownLatch;

  public class MyThread2 extends Thread

  {

  private CountDownLatch count;

  public MyThread2(CountDownLatch count, String name)

  {

  this.count = count;

  this.setName(name);

  }

  @Override

  public void run()

  {

  System.out.println(this.getName() + " staring…");

  System.out.println(this.getName() + " end…");

  this.count.countDown();

  }

  /**

  * @param args

  */

  public static void main(String[] args)

  {

  System.out.println("main thread starting…");

  CountDownLatch count = new CountDownLatch(5);

  for (int i = 1; i <= 5; i++)

  {

  MyThread2 my = new MyThread2(count, "Thread " + i);

  my.start();

  }

  try

  {

  count.await();

  }

  catch (InterruptedException e)

  {

  e.printStackTrace();

  }

  System.out.println("main thread end…");

  }

  }

  运行结果如下:

  main thread starting…

  Thread 2 staring…

  Thread 2 end…

  Thread 4 staring…

  Thread 4 end…

  Thread 1 staring…

  Thread 1 end…

  Thread 3 staring…

  Thread 3 end…

  Thread 5 staring…

  Thread 5 end…

  main thread end…