现在有T1、T2、T3三个线程，你怎样保证T2在T1执行完后执行，T3在T2执行完后执行？使用join

public class ThreadTest extends Thread{
	private int j = 1;
	public ThreadTest(String name){
		setName(name);
	}
	
	@Override
	public void run() {
		// TODO Auto-generated method stub
		//super.run();
		for(int i=1;i<1000000;i++){
			j++;
		}
		System.out.println("线程"+Thread.currentThread().getName()+"执行完毕"+j);
	}
	
	public static void main(String[] args) throws InterruptedException {
		Thread t1 = new Thread(new ThreadTest("T1")); 
		Thread t2 = new Thread(new ThreadTest("T2")); 
		Thread t3 = new Thread(new ThreadTest("T3"));

		t1.start(); 
		t1.join();

		t2.start(); 
		t2.join();

		t3.start(); 
		t3.join();
	}

}

主要使用的join方法实现，直到当前线程执行完才会唤醒其他线程继续执行