Designing Classes, needing stubs

[Paul Johnson]

I came across an issue yesterday and I suppose people who design OO
software must face it all the time, but for a moment I was surprised and
made a note to ask about it.   What do you do when a superclass has a
method that includes calls to other methods that are implemented in the
subclasses?  I found myself creating hollow (call it a stub?) methods in
the superclass to stop the compiler from complaining.

Let me explain.

There is a class A.  Instances of A are never created, rather there are
subclasses B and C.  B and C have specialized implementations of a
method, say we call it handleProblem.    All of the other things that B
and C do are inherited from A.  A does not have a handleProblem method.

In the class A, there is a "step" method that outlines a number of
things to do, and one of them is [self handleProblem].   This step
method is called from ModelSwarm in the usual way, it tells each agent
to do a series of actions.  The "step" method is defined in the
superclass A, and there is no need to specialize it in B and C.
However, when I try to compile, I get the understandable compiler
warning that class A does not respond to handleProblem.   However, since
I never create any objects of class A, only the subclasses B and C, the
warning is not important.

To make it go away, the only thing I could think of was to put a stub in
A for the -handleProblem method, and then have the specialized actions
in B and C override.  Good, bad, or indifferent?

--
Paul E. Johnson                       email: address@hidden
Dept. of Political Science            http://lark.cc.ukans.edu/~pauljohn
University of Kansas                  Office: (785) 864-9086
Lawrence, Kansas 66045                FAX: (785) 864-5700




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