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

[Anant R. <ar...@21...>]

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...<mailto: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.
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