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

两个类都加上空参数的构造函数

public Point3D(int a,int b ,int c)
    {
      super(x ,y);
      z=c;
     }
里面s，y，改成a，b

哦，谢谢，是什么意思呢

为什么要那样改。。。

您好，很高兴能帮到您：修改后的代码及注释如下：
int x , y ;
      double s;
      Point2D(){    /*空构造函数*/
         
      }
      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{   /*Point3D是子类继承父类Point2D,既继承了父类已有的属性和方法*/
     int z;
     public Point3D(){        /*空构造函数*/
         
     }
     
     public Point3D(int a,int b ,int c)   
     {
       super(a,b);            /*super(a,b)其实是在子类构造方法中重写了父类的构造方法，所以形参是子类的形参a,b*/
       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));/*new Point2D()是一个空构造方法，因为你已经重新定义，所以系统默认的被覆盖，需重新定义一个空构造方法*/
      System.out.println(new Point3D().distance(p3d1,p3d2));/*new Point3D()也是一个空构造方法*/
 }
 }