在某个线程中调用另一个线程的join方法，是将当前的cpu让给另一个线程，等到规定的时间到了或另一个线程执行结束后，自己再执行。

package test;

public class TestJoin1 {
	
	public static void main(String[] args) throws InterruptedException {
		
		TheOtherThread tot = new TheOtherThread();
		Thread t = new Thread(tot);
		t.start();
		//t.join();
		System.out.println("main");
	}
	
}


class TheOtherThread implements Runnable{

	@Override
	public void run() {
		try {
			for (int i = 0; i < 10; i++) {
				Thread.sleep(1000);
				System.out.println(i);
			}
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
	}
	
}

main
0
1
2
3
4
5
6
7
8
9

0
1
2
3
4
5
6
7
8
9
main

package test;

import java.util.Date;

public class TestJoin {

	public static void main(String[] args) {
		
		DateThreat dt1 = new DateThreat("a");
		DateThreat dt2 = new DateThreat("b");
	
		Thread t1 = new Thread(dt1);
		Thread t2 = new Thread(dt2);
		
		DateThreat dt3 = new DateThreat("c",t2);
		Thread t3 = new Thread(dt3);

		
		t1.start();
		t2.start();
		t3.start();
		
	}
	
}

class DateThreat implements Runnable{
	
	private String name ;
	
	private Thread t;
	
	public DateThreat(String name) {
		this.name = name;
	}
	
	public DateThreat(String name,Thread t) {
		this.name = name;
		this.t = t;
	}

	@Override
	public void run() {
		
		try {
			System.out.println(this.name + " begin : " + new Date());
			if(t != null){
				t.join();
			}
			for(int i =0;i<10;i++){
				Thread.sleep(1000);
				System.out.println(this.name + " : " + i);
			}
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		System.out.println(this.name + " end : " + new Date());
		
	}
	
	
}

结果会是：

c begin : Tue Aug 12 17:59:16 CST 2014
b begin : Tue Aug 12 17:59:16 CST 2014
a begin : Tue Aug 12 17:59:16 CST 2014
b : 0
a : 0
b : 1
a : 1
b : 2
a : 2
b : 3
a : 3
b : 4
a : 4
b : 5
a : 5
b : 6
a : 6
b : 7
a : 7
b : 8
a : 8
b : 9
b end : Tue Aug 12 17:59:26 CST 2014
a : 9
a end : Tue Aug 12 17:59:26 CST 2014
c : 0
c : 1
c : 2
c : 3
c : 4
c : 5
c : 6
c : 7
c : 8
c : 9
c end : Tue Aug 12 17:59:36 CST 2014