2019独角兽企业重金招聘Python工程师标准>>> 
ThreadGroup:多个相同功能的线程可合并到一个线程组中。线程组可用于监控组里面的活动线程数，同时操作多个线程，wait,notify。等等。。
同时可为线程组和各个线程命名。
/**
* Created by li on 2016/11/24.
*/
public class DemoThread extends Thread {
private final static Object object = new Object();
public static void main(String[] args) throws InterruptedException {
ThreadGroup threadGroup = new ThreadGroup("myGroup");
Thread thread1 = new Thread(threadGroup, new DemoThread(), "t1");
Thread thread2 = new Thread(threadGroup, new DemoThread(), "t2");
thread1.start();
thread2.start();
System.out.println(threadGroup.activeCount());
System.out.println("主线程干的事");
Thread.sleep(5000);
System.out.println(threadGroup.activeCount());
}
@Override
public void run() {
System.out.println(Thread.currentThread().getThreadGroup().getName() + "++" + Thread.currentThread().getName());
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}