import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;

public class Main {
  public static void main(String[] args) throws Exception {
    Runnable myRunnable = new Runnable() {
      @Override
      public void run() {
        try {
          System.out.println("Start: " + Thread.currentThread().getName());
          Thread.sleep(100);
        } catch (InterruptedException e) {
          throw new RuntimeException(e);
        }
      }
    };
    Thread one = new Thread(myRunnable);
    Thread two = new Thread(myRunnable);
    one.start();
    two.start();

    List<Thread> threads = getThreadsFor(myRunnable);
    for (Thread thread : threads)
      System.out.println("Found: " + thread.getName());
  }

  private static List<Thread> getThreadsFor(Runnable myRunnable)
      throws Exception {
    Method getThreads = Thread.class.getDeclaredMethod("getThreads");
    Field target = Thread.class.getDeclaredField("target");
    target.setAccessible(true);
    getThreads.setAccessible(true);
    Thread[] threads = (Thread[]) getThreads.invoke(null);
    List<Thread> result = new ArrayList<Thread>();
    for (Thread thread : threads) {
      Object runnable = target.get(thread);
      if (runnable == myRunnable)
        result.add(thread);
    }
    return result;
  }
}