java.lang.ThreadGroup.activeCount()方法返回此线程组中活动线程数的估计值。

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

public int activeCount()

NA

此方法返回此线程组以及将此线程组作为祖先的任何其他线程组中的活动线程数的估计值。

NA

以下示例显示了java.lang.ThreadGroup.activeCount（）方法的用法。

package com.iowiki;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.\");

让我们编译并运行上面的程序，这将产生以下结果 -

Starting Thread-0...Starting Thread-1...Active threads in \"Parent ThreadGroup\" = 2Thread-0 finished executing.Thread-1 finished executing.