java - unable to predict when all the threads have finished execution -

here code

package pe.entel.ftp;  public class myclass implements runnable {     public void run() {         system.out.println(thread.currentthread().getname());     }     public static void main(string[] args) {         myclass runnable = new myclass();         threadgroup tg1 = new threadgroup("parent threadgroup");          (int = 0; < 100; i++) {             thread t1 = new thread(tg1, runnable, + "");             t1.start();             system.out.println("thread group name: " + tg1.getname());          }         while (tg1.isdestroyed()) {             system.out.println("yes success");         }          system.out.println("completed");      } } 

while part of o/p

  thread group name: parent threadgroup   thread group name: parent threadgroup   thread group name: parent threadgroup   thread group name: parent threadgroup   thread group name: parent threadgroup  completed  84   86  88  90  92  94  96  98  95  97  99 

here unable predict when thread group completing execution.even ,while loop checking whether thread group destroyed not working.even after printing completed threads executing.

a threadgroup not complete execution. if want wait threads finish, have collect them , wait of them:

list<thread> allthreads = new arraylist<>();  (int = 0; < 100; i++) {   thread t1 = new thread(tg1, runnable, + "");         t1.start();    allthreads.add(t1);   }  allthreads.foreach(thread::join); 

threadgroups exist longer threads contain, might want add new threads threadgroup after threads have finished. merely grouping threads, not controlling them.