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From "Christopher (siege) "OBrien <>
Subject RE: [COLLECTIONS] Some more lobbying for the OrderedSet class
Date Tue, 29 Apr 2003 20:57:53 GMT

I believe you're looking for a LinkedHashSet. You'll need to implement
your own name-searching methods of course, but that's no longer abstract
enough for a general-purpose collection, really.

- Chris

On Tue, 2003-04-29 at 15:57, TREPANIER, ERIC wrote:
> Hello,
> I am working on a project for which I had a need for a specialized type of
> collection that would support the following features:
> - Elements stored in the collection are ordered
>   (cardinal order, similar to List)
> - Element duplicates are typically not accepted
>   (although in some cases, it might make sense to have duplicates)
> - In addition to their cardinal orders, elements can be searched by their
> name property
>   (in my case, element names are unique, but it is plausible that in some
> cases, two distinct elements might have the same name, i.e. a Person)
> I have dug through the Java Collections API as well as the Jakarta Commons
> Collection library, but I did not find a single class that does what I want.
> Basically, I need to keep two arrays in sync, one, which has the list of
> names and the other which has the actual objects. This way, I can access an
> object directly by its index, through the object array - or - I can search
> for a name (String) in the name array and use the resulting index to return
> the object from the object array.
> In any case, I went ahead and created an implementation that fits my
> particular needs. I believe it is a genuinely useful and reusable
> implementation and I would like to contribute it to the Jakarta Commons
> project, quite possibly to be integrated into the Collections project.
> Certainly, the idea is not new and it sounds like the List/Set combination
> mentioned in the message below, but my implementation is somewhat different.
> What I have so far is a small, stand-alone project, which includes:
> - 3 java source files (java/src) for the solution implementation (1 class
> and 2 interfaces, with full javadoc comments)
> - 7 java source files (java/test) for the junit test cases, 5 of which are
> directly taken from the Commons Collections project (BulkTest, TestAll,
> TestCollection, TestList and TestObject).
> - A build.xml file which is basically a subset of the Commons Collections
> Ant build file
> Basically, I have one class, called Catalog, which implements a custom
> extension of the List interface.
> The Catalog class successfully completes all the test cases from
> (it implements an interface which itself extends the List
> interface), however I have not yet defined test cases for the specialized
> methods of the custom interface.
> Do you have any interest for this code, and if so, what should I do? Can I
> post it to this list?
> Regards,
> Eric Trepanier
> -----Original Message-----
> From:
> [] 
> Sent: April 29, 2003 1:39 PM
> To:;
> Subject: Re: [COLLECTIONS] Some more lobbying for the OrderedSet class
> I strongly agree that a ListSet interface that extends both List and Set is
> the most intuitive way to go.  "List" and "Set" are understood by Java
> developers anywhere and to have a "ListSet" interface would make it very
> clear what it means.
> Eric Pabst
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Christopher (siege) O'Brien <>

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