Как получить список живых нитей из группы ThreadGroup? Как получить список мертвых нитей из группы ThreadGroup?

Main.java

package com.examples;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;

public class Main {
    public static List<Thread> threads = new ArrayList<>();
    public static void main(String[] args) throws InterruptedException {
        Random random = new Random();
        final ThreadGroup group1 = new ThreadGroup("GROUP 1");
        for (int i = 1; i <= 100; i++) {
            Thread thread = new Thread(group1, "THREAD №" + i) {
                @Override
                public void run() {
                    final boolean randomBoolean = random.nextBoolean();
                    while (!isInterrupted()) {
                        try {
                            if (randomBoolean) {
                                Thread.sleep(random.nextInt(5000));
                                this.interrupt();
                            }
                        } catch (InterruptedException e) {
                            System.out.println(getName() + " : " +
                                    getThreadGroup().getName() + " прервана");
                        }
                    }
                }
            };
            threads.add(thread);
            thread.start();
        }
        Thread.sleep(2500);
        List<Thread> runnable = getAllThreads(Thread.State.RUNNABLE, threads);
        System.out.printf("Runnable amount: %s%n", runnable.size());
        List<Thread> timedWaiting = getAllThreads(Thread.State.TIMED_WAITING, threads);
        System.out.printf("Timed waiting amount: %s%n", timedWaiting.size());
        List<Thread> terminated = getAllThreads(Thread.State.TERMINATED, threads);
        System.out.printf("Terminated amount: %s%n", terminated.size());
        
        if (terminated.size() > 0)
            System.out.println(null == terminated.get(0).getThreadGroup()); // TRUE !!!
        
        for (Thread thread : runnable) {
            thread.interrupt();
        }
    }

    public static List<Thread> getAllThreads(final Thread.State state, List<Thread> threadList ) {
        List<Thread> found = new ArrayList<>();
        for (Thread thread : threadList)
            if (thread.getState() == state)
                found.add(thread);
        return found;
    }
}