Java - ThreadGroup class

Introduction

The Java ThreadGroup class represents a set of threads. It can also include other thread groups. The thread groups form a tree in which every thread group except the initial thread group has a parent.

Class Declaration

Following is the declaration for java.lang.ThreadGroup class −

public class ThreadGroup
   extends Object
      implements Thread.UncaughtExceptionHandler

Class constructors

Class methods

Methods inherited

This class inherits methods from the following classes −

• java.lang.Object

Using ThreadGroups to group threads Example

Following example showcases the usage of ThreadGroup in a multithreaded program.

package com.tutorialspoint;

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.");
   }
} 

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

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