Re: Design/Inheritance Question

From:
Patricia Shanahan <pats@acm.org>
Newsgroups:
comp.lang.java.programmer
Date:
Sun, 29 Oct 2006 15:34:56 GMT
Message-ID:
<AS31h.1319$zf.514@newsread3.news.pas.earthlink.net>
Bruce Feist wrote:

Chris Uppal wrote:

....

it suggests that your hierarchy is focussed on
the wrong aspects of a cell. Presumably, for a maze, the /most/
important fact
is its topology -- not the geometrical shape -- so I'd expect the class
hierarchy to follow that.


That makes sense, although I'm frankly not sure how to do that.
Geometric categorization is easy; I have convenient names and concepts
for most of the shapes involved. Topological categorization is more
difficult for me, because each topology for the cell seems independent,
and I don't have language to describe them -- I don't want to end up
with obscure names that I cannot mentally associate with the meanings of
the classes. I suppose I could manufacture meaningful names somehow out
of the connectivity information... tricky.

....

Here's a possible compromise. Define an interface Topology with methods
that return things like lists of neighbors.

Add to the abstract base class for the cells a method:

public abstract Topology getTopology();

For any cell type where there is a single topology that applies, make
the cell class implement Topology, and return itself:

public Topology getTopology(){
   return this;
}

For a cell type where you want to use a separate Topology, for example
one shared with some cases of another cell type, have a non-trivial
getTopology method:

public Topology getTopology(){
   if(conditions for special case){
     return new SomeTopologyClass(parameters);
   }else{
     return this;
   }
}

Within the cell hierarchy, you can vary the extent to which Topology is
merged with cell type or separate, without affecting any other code.

Patricia

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