Java.lang.ThreadGroup.enumerate() Method

Description

The java.lang.ThreadGroup.enumerate(ThreadGroup[] list, boolean recurse) method copies into the specified array references to every active subgroup in this thread group. If the recurse flag is true, references to all active subgroups of the subgroups and so forth are also included.

Declaration

Following is the declaration for java.lang.ThreadGroup.enumerate() method

public int enumerate(ThreadGroup[] list, boolean recurse)

Parameters

• list -- This is an array into which to place the list of thread groups.

• recurse -- This is a flag indicating whether to recursively enumerate all included thread groups.

Return Value

This method returns the number of thread groups put into the array.

Exception

• SecurityException -- if the current thread does not have permission to enumerate this thread group.

Example

The following example shows the usage of java.lang.ThreadGroup.enumerate() method.

package com.tutorialspoint;

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 thread groups put into the array with
         flag as true */
         ThreadGroup[] grpList = new ThreadGroup[pGroup.activeGroupCount()];
         int count = pGroup.enumerate(grpList, true);
         for (int i = 0; i < count; i++) {
            System.out.println("ThreadGroup" + grpList[i].getName() +
            " found");
         }

         // 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.");
   }
} 

Let us compile and run the above program, this will produce the following result:

Starting Thread-0...
Starting Thread-1...
ThreadGroup Child ThreadGroup found
Thread-0 finished executing.
Thread-1 finished executing.