Java ThreadGroup class

// Demonstrate thread groups.
class NewThread extends Thread {
  boolean suspendFlag;

  NewThread(String threadname, ThreadGroup tgOb) {
    super(tgOb, threadname);
    System.out.println("New thread: " + this);
    suspendFlag = false;/* w ww.j  a  v  a 2s. c  o  m*/
    start(); // Start the thread
  }

  // This is the entry point for thread.
  public void run() {
    try {
      for(int i = 5; i > 0; i--) {
        System.out.println(getName() + ": " + i);
        Thread.sleep(1000);
        synchronized(this) {
          while(suspendFlag) {
            wait();
          }
        }
      }
    } catch (Exception e) {
      System.out.println("Exception in " + getName());
    }
    System.out.println(getName() + " exiting.");
  }

  synchronized void mysuspend() {
    suspendFlag = true;
  }

  synchronized void myresume() {
    suspendFlag = false;
    notify();
  }
}

public class Main {
  public static void main(String args[]) {
    ThreadGroup groupA = new ThreadGroup("Group A");
    ThreadGroup groupB = new ThreadGroup("Group B");

    NewThread ob1 = new NewThread("One", groupA);
    NewThread ob2 = new NewThread("Two", groupA);
    NewThread ob3 = new NewThread("Three", groupB);
    NewThread ob4 = new NewThread("Four", groupB);

    System.out.println("\nHere is output from list():");
    groupA.list();
    groupB.list();
    System.out.println();

    System.out.println("Suspending Group A");
    Thread tga[] = new Thread[groupA.activeCount()];
    groupA.enumerate(tga); // get threads in group
    for(int i = 0; i < tga.length; i++) {
      ((NewThread)tga[i]).mysuspend(); // suspend each thread
    }

    try {
      Thread.sleep(4000); 
    } catch (InterruptedException e) {
      System.out.println("Main thread interrupted.");
    }

    System.out.println("Resuming Group A");
    for(int i = 0; i < tga.length; i++) {
      ((NewThread)tga[i]).myresume(); // resume threads in group
    }

    // wait for threads to finish
    try {
      System.out.println("Waiting for threads to finish.");
      ob1.join();
      ob2.join();
      ob3.join();
      ob4.join();
    } catch (Exception e) {
      System.out.println("Exception in Main thread");
    }

    System.out.println("Main thread exiting.");
  }
}