java.lang.ThreadGroup.activeGroupCount() 方法返回活动线程组的数目估计值。

声明

以下是java.lang.ThreadGroup.activeGroupCount()方法的声明

public int activeGroupCount()

参数

• NA

返回值

此方法返回活动线程组的数量与该线程组作为祖先。

异常

• NA

例子

下面的例子显示java.lang.ThreadGroup.activeGroupCount()方法的使用。

package com.yiibai;

import java.lang.*;

public class ThreadGroupDemo implements Runnable
{
   public static void main(String[] args) {
      ThreadGroupDemo tg = new ThreadGroupDemo();
      tg.func();
   }

   public void func() {
      try {     
         // create a parent ThreadGroup
         ThreadGroup pGroup = new ThreadGroup("Parent ThreadGroup");
    
         // create a child ThreadGroup for parent ThreadGroup
         ThreadGroup cGroup = new ThreadGroup(pGroup, "Child ThreadGroup");

         // create a thread
         Thread t1 = new Thread(pGroup, this);
         System.out.println("Starting " + t1.getName() + "...");
         t1.start();
            
         // create another thread
         Thread t2 = new Thread(cGroup, this);
         System.out.println("Starting " + t2.getName() + "...");
         t2.start();
            
         /* returns the number of active thread groups with this 
         thread group as an ancestor */
         System.out.println("Active group(child) threads in "" + 
         pGroup.getName() + "" = " + pGroup.activeCount());

         // block until the other threads finish
         t1.join();
         t2.join();
      }
      catch (InterruptedException ex) {
         System.out.println(ex.toString());
      }
   }

   // implements run()
   public void run() {

      for(int i=0;i<1000;i++) {
         i++;
      }
      System.out.println(Thread.currentThread().getName() + 
      " finished executing.");
   }
} 

让我们来编译和运行上面的程序，这将产生以下结果：

Starting Thread-0...
Starting Thread-1...
Active group(child) threads in "Parent ThreadGroup" = 1
Thread-0 finished executing
Thread-1 finished executing