Re: OO should break when broken

[Guy Steele - Sun Microsystems Labs <address@hidden>]

   Date: Thu, 4 Sep 2003 15:57:14 -0400
   Subject: Re: OO should break when broken
   Cc: ll1-discuss <ll1-discuss@ai.mit.edu>
   To: Colin Putney <cputney@wiresong.ca>
   From: John Clements <clements@brinckerhoff.org>
   
   
   On Thursday, September 4, 2003, at 02:59  PM, Colin Putney 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.

--Guy Steele