thread.Join把指定的线程加入到当前线程，可以将两个交替执行的线程合并为顺序执行的线程。比如在线程B中调用了线程A的Join()方法，直到线程A执行完毕后，才会继续执行线程B。

package com.wzs;

/**
 * Java多线程中join用法
 * 
 * @author Administrator
 * 
 */
public class JoinTest {
	public static void main(String[] args) {
		BThread bThread = new BThread("-BThread-");
		AThread aThread = new AThread(bThread, "-AThread-");
		bThread.start();
		aThread.start();
	}
}

class AThread extends Thread {
	BThread bThread;

	public AThread(BThread bThread, String str) {
		super(str);
		this.bThread = bThread;
	}

	@Override
	public void run() {
		for (int i = 0; i < 5; i++) {
			System.out.println(Thread.currentThread().getName() + " : " + i);
			try {
				bThread.join();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}
}

class BThread extends Thread {
	public BThread(String str) {
		super(str);
	}

	@Override
	public void run() {
		for (int i = 0; i < 5; i++) {
			System.out.println(Thread.currentThread().getName() + " : " + i);
			try {
				Thread.sleep(1000);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}
}

-BThread- : 0
-AThread- : 0
-BThread- : 1
-BThread- : 2
-BThread- : 3
-BThread- : 4
-AThread- : 1
-AThread- : 2
-AThread- : 3
-AThread- : 4