ThreadGroup.activeCount() has the following syntax.
public int activeCount()
In the following code shows how to use ThreadGroup.activeCount() method.
public class Main { // w w w. java 2 s. c om public static void main(String[] args) { ThreadGroupDemo tg = new ThreadGroupDemo(); } } class ThreadGroupDemo implements Runnable { public ThreadGroupDemo() { ThreadGroup pGroup = new ThreadGroup("Parent ThreadGroup"); ThreadGroup cGroup = new ThreadGroup(pGroup, "Child ThreadGroup"); Thread t1 = new Thread(pGroup, this); System.out.println("Starting " + t1.getName()); t1.start(); Thread t2 = new Thread(cGroup, this); System.out.println("Starting " + t2.getName()); t2.start(); System.out.println("Active threads in \"" + pGroup.getName() + "\" = " + pGroup.activeCount()); } public void run() { System.out.println(Thread.currentThread().getName() + " finished executing."); } }
The code above generates the following result.