java线程问题

上次老师讲了一个java线程的问题，蛮有趣的，和大家啊分享一下……

代码如下：class ThreadA extends Thread
{
private ThreadAdd threadAdd;

ThreadA(ThreadAdd t)
{
threadAdd = t;
}

public void run()
{
for (int i=1; i<= 10; i++) {
threadAdd.add(i);
System.out.println("threadA:" + i);
try {
sleep(100);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}

class ThreadB extends Thread
{
private ThreadAdd threadAdd;

ThreadB(ThreadAdd t)
{
threadAdd = t;
}

public void run()
{
for (int i=11; i<= 20; i++) {
threadAdd.add(i);
System.out.println("threadB:" + i);
try {
sleep(100);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

}
}

public class ThreadAdd {

private int sum = 0;

public void add(int num)
{
sum += num;
}

public void print()
{
System.out.println("sum = " + sum);
}

public static void main(String[] args) {
ThreadAdd threadAdd = new ThreadAdd();
ThreadA threadA = new ThreadA(threadAdd);
ThreadB threadB = new ThreadB(threadAdd);

threadA.start();
threadB.start();

while(threadA.isAlive() || threadB.isAlive())
;

threadAdd.print();
}
}

//结果如下：

线程1：0
线程2：5
线程1：1
线程2：6
线程2：7
线程1：2
线程2：8
线程1：3
线程2：9
线程1：4
sum=45