code: public static Thread[] getThreads(ThreadGroup group) {
  		final Thread[] slackList = new Thread[group.activeCount() * 2];
  		final int actualSize = group.enumerate(slackList);
  		final Thread[] result = new Thread[actualSize];
  		System.arraycopy(slackList, 0, result, 0, actualSize);
  		return result;
  	}
docs: 获取JVM中与当前线程同组的所有线程<br>
  使用数组二次拷贝方式，防止在线程列表获取过程中线程终止<br>
  from Voovan
  
  @param group 线程组
  @return 线程对象数组