class Point2D{
     int x , y ;
     double s;
     Point2D(int a ,int b)
    {
      x=a;
      y=b;
     }
     void offset(int a,int b)
    {
      x=x+a;
      y=y+b;
     }
     double distance(Point2D p1,Point2D p2)
    {
       double m;
       m = Math.sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));
       return m;
     }
}


public  class Point3D extends Point2D{
    int z;
    public Point3D(int a,int b ,int c)
    {
      super(x ,y);
      z=c;
     }
    void offset(int a,int b,int c)
    {   x=x+a;
        y=y+b;
        z=z+c;
     }
    double distance(Point3D p1,Point3D p2)
    {
       double m;
       m = Math.sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y)+(p1.z-p2.z)*(p1.z-p2.z));
       return m;
     }
    public static void main(String args[]){
     Point2D p2d1= new Point2D(2,3);
     Point2D p2d2= new Point2D(4,5);
     Point3D p3d1= new Point3D(2,2,2);
     Point3D p3d2= new Point3D(3,3,3);
     System.out.println(new Point2D().distance(p2d1,p2d2));
     System.out.println(new Point3D().distance(p3d1,p3d2));
}
}

总是出错，怎么回事啊

哦，谢谢，是什么意思呢

为什么要那样改。。。