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From "James Carman" <>
Subject RE: [collections] MultiMaps...
Date Fri, 13 May 2005 17:28:52 GMT
Upon further thought, why do we even have a class like MultiHashMap?
Couldn't we write a generic MultiMap implementation that wraps another map
and provides the "multiple" functionality?

public class MapUtils
  public static MultiMap multiMap( Map implementation );
  public static MultiMap multiMap( Map implementation, Factory
collectionFactory );

-----Original Message-----
From: James Carman [] 
Sent: Friday, May 13, 2005 1:21 PM
To: 'Jakarta Commons Developers List'
Subject: [collections] MultiMaps...

I have a case in my application where I want to map one key to multiple
values.  However, I don't want the values to be stored as a List.  I would
rather have MultiHashMap store the values in a Set of some kind (HashSet
maybe).  It would be nice if I could tell MultiHashMap what kind of
collection to use to store the values.  Maybe we could parameterize the

public MultiHashMap( Factory factory )

The factory would be used to create a collection instance each time one is
needed for a new key in the map.  Maybe this is overkill and we could just
give it a Class instance and it can call newInstance() on that.  Anyway,
that would allow MultiHashMap to return any kind of collection, not just
Lists.  Of course, I could just create a new Set using the returned List,
but that's a lot of objects to create.  What do you guys think?

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