Re: [jgrapht-users] Impossible to set source and target of DefaultEdge

[John S. <js...@gm...>]

It's a default edge implementation meant as a companion to the
out-of-the-box graph implementations.  It's rare to need to write your
own graph implementation from scratch (rather than extending or
decorating one of the out-of-the-box ones), but if you do, then
providing your own edge implementation is going to be the least of
your concerns.

JVS

On Mon, Jul 11, 2011 at 10:43 AM, Anant Rathi <ar...@21...> wrote:
> Hey Rob,
>
>
>
> Thanks for your response. I understand that EdgeFactories are much preferred
> to constructors and that graphs are used to query source and target, but in
> the case of DefaultEdge, I don’t see how it’s possible for the system to
> work.
>
>
>
> A factory that constructs DefaultEdges cannot set their source and target.
> And calling getEdgeSource() or getEdgeTarget() on a
> Graph<whatever,DefaultEdge> is essentially meaningless since every pair of
> DefaultEdges in the graph are equal().
>
>
>
> I’ve investigated the source code a bit further, and DefaultEdge extends
> IntrusiveEdge, which has the source and target members’ scope as
> package-private. So graph implementations provided by JGraphT itself
> (DefaultDirectedGraph, etc.) can (and do) set the source and target of
> DefaultEdges , and therefore can (and do) correctly implement
> getEdgeSource() and getEdgeTarget(). But for the rest of us, I think it’s
> impossible to guarantee correctness of these two methods when Defaultedge is
> the edge type.
>
>
>
> Anant
>
>
>
> From: Rob Patro [mailto:rob...@gm...]
> Sent: Monday, July 11, 2011 12:07 PM
> To: jgr...@li...
> Subject: Re: [jgrapht-users] Impossible to set source and target of
> DefaultEdge
>
>
>
> Hi Anant,
>
>   JGraphT is a very well designed library, but takes some getting used to at
> first.  Edges are created using the EdgeFactors; raw Edges are not
> constructed.  Then the src and target are queried via the graph in which the
> edge exists.
>
> --Rob
>
> On Jul 11, 2011 11:59 AM, "Anant Rathi" <ar...@21...> wrote:
>> All,
>>
>> org.jgrapht.graph.DefaultEdge has protected getSource() and getTarget()
>> methods, but there aren't setters for source and target or a constructor
>> that sets them. Whether you are instantiating or extending DefaultEdge, the
>> source and target members can't be modified, and they're always null. That
>> doesn't seem right.
>>
>> Am I missing something?
>>
>> Anant Rathi
>> Research Intern
>> 21st Century Technologies, Inc.
>> 6011 W. courtyard Drive
>> Building 5, Suite 300
>> Austin, TX 78730
>>
>> Phone: 512 682 4707
>> Email: ar...@21...
>> URL: http://www.21technologies.com
>>
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>
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