How to copy using enumerate() method in Java?

public static void main(String[] args) throws InterruptedException {
    ThreadGroup myGroup = new ThreadGroup("MyGroup");
    Thread thread = new Thread(myGroup,()->{
        while (true){
            try{
                TimeUnit.SECONDS.sleep(1);
            }catch (InterruptedException e){
                e.printStackTrace();
            }
        }
    },"MyThread");
    thread.start();
    TimeUnit.MILLISECONDS.sleep(1);
    ThreadGroup mainGroup = currentThread().getThreadGroup();
    Thread[] list = new Thread[mainGroup.activeCount()];
    int recurseSize = mainGroup.enumerate(list);
    System.out.println(recurseSize);
    recurseSize = mainGroup.enumerate(list,false);
    System.out.println(recurseSize);
}