帮帮忙

class methoddemo1
{
  float add(float x,float y)
  {
    float z;
    z = x + y;
    return z;
  }
}
class trymethoddemo1
{
  public static void main(String args[])
  {
    methoddemo1 a=new methoddemo1();
    System.out.println(a.add(1,9));
  }
}上面程序运行后怎么会出现“Exception in thread "main" java.lang.NoClassDefFoundError: canshu”的错误啊。怎么解决，请帮忙啊，谢了！