一个小问题

[xu_guanghui]

下面这个程序是关于java多线程的一个例子
编译没有问题,但当我执行的时候 java Threadtest提示
Exception in thread "main" java.lang.NoClassDefFoundError: Threadtest

不知道是怎么回事情,望各位指点,刚学JAVA 不太清楚
class MyThread extends Thread
{
public void run()
{
for (int cnt=0;cnt<5;cnt++)
{
System.out.println(Thread.currentThread()+"的运行次数是:" +cnt);
try
{
Thread.currentThread().sleep((int)(Math.random()*100));
}catch(InterruptedException e){}
}
}
}

public class Threadtest
{
static public void main(String args[])
{
Thread myThreadA=new Thread (new MyThread(),"threadA");
Thread myThreadB=new Thread (new MyThread(),"threadB");

myThreadA.start();
myThreadB.start();

try{
Thread.currentThread().sleep(1000);
}
catch(InterruptedException e){}

System.out.println(Thread.currentThread());
}
}