java.lang.ThreadGroup.activeCount() 方法返回活动线程在该线程组的数目的估计值。

声明

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

public int activeCount()

参数

• NA

返回值

此方法返回此线程组和具有该线程组作为祖先的任何其它线程组活动线程的数目的估计值。

异常

• NA

例子

下面的例子显示java.lang.ThreadGroup.activeCount()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();
            
         // display the number of active threads 
         System.out.println("Active 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 threads in "Parent ThreadGroup" = 2
Thread-0 finished executing
Thread-1 finished executing