java.lang.ThreadGroup，ThreadGroup有很多優(yōu)勢(shì)，最重要的一點(diǎn)就是它可以對(duì)線程進(jìn)行遍歷，知道那些線程已經(jīng)運(yùn)行完畢，還有那些線程在運(yùn)行。關(guān)于ThreadGroup的使用代碼如下：

  

class MyThread extends Thread { 
	boolean stopped; 
	MyThread(ThreadGroup tg, String name) { 
		super(tg, name);
		stopped = false; 
	} 
	public void run() {
		System.out.println(Thread.currentThread().getName() + " starting.");
		try {
			for (int i = 1; i < 1000; i++) {
				System.out.print(".");
				Thread.sleep(250);
				synchronized (this) {
					if (stopped)break;
				}
			}
		} catch (Exception exc) {
			System.out.println(Thread.currentThread().getName() + " interrupted.");
		}
		System.out.println(Thread.currentThread().getName() + " exiting.");
	}
	synchronized void myStop() {
		stopped = true;
	}
}
public class Main {
	public static void main(String args[]) throws Exception {
		ThreadGroup tg = new ThreadGroup("My Group");
		MyThread thrd = new MyThread(tg, "MyThread #1");
		MyThread thrd2 = new MyThread(tg, "MyThread #2");
		MyThread thrd3 = new MyThread(tg, "MyThread #3");
		thrd.start();
		thrd2.start();
		thrd3.start();
		Thread.sleep(1000);
		System.out.println(tg.activeCount() + " threads in thread group.");
		Thread thrds[] = new Thread[tg.activeCount()];
		tg.enumerate(thrds);
		for (Thread t : thrds)
			System.out.println(t.getName());
		thrd.myStop();
		Thread.sleep(1000);
		System.out.println(tg.activeCount() + " threads in tg.");
		tg.interrupt();
	}
}

1.ThreadGroup可以遍歷線程，知道那些線程已經(jīng)運(yùn)行完畢，那些還在運(yùn)行 

2.可以通過(guò)ThreadGroup.activeCount知道有多少線程從而可以控制插入的線程數(shù)