Re: OO should break when broken

[Colin Putney <address@hidden>]

On Thursday, September 4, 2003, at 01:28 PM, Guy Steele - Sun 
Microsystems Labs wrote:

>> Unless somebody wants to post code in an OO language showing an
>> implementation of Circle as a useful subclass of Ellipse, this is my
>> last post in this thread.
>
>    Ellipse.java:
>    class Ellipse extends Object {
>         float long_axis;
>         float short_axis;
>
>         public Ellipse(float long_axis_init, float short_axis_init)
>         {
>    	long_axis = long_axis_init;
>    	short_axis = short_axis_init;
>         }
>    }
>
>    Circle.java:
>    class Circle extends Ellipse {
>
>         public Circle(float radius)
>         {
>             super(radius, radius);
>         }
>    }
>
>
> Very nice, but let
>
>    float radius = 3;
>    Ellipse e = new Ellipse(radius, radius);
>
> and then, alas,
>
>    e instanceof Circle
>
> is false.

Not only that, it's pointless to have the subclass at all. You get the 
same effect with this:

    Ellipse.java:
    class Ellipse extends Object {
         float long_axis;
         float short_axis;

         public Ellipse(float long_axis_init, float short_axis_init)
         {
    	long_axis = long_axis_init;
    	short_axis = short_axis_init;
         }
	
	public Ellipse(float radius)
	{
	  long_axis = radius;
	  short_axis = radius;
	}

    }