Thread: [jgrapht-users] Weighted graphs

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Hi all,

As I am trying to work with weighted graphs, I've come across a problem I
don't understand.
My weighted graph contains vertices of type ISynsetID and edges of
IPointer. The former gives no problems, but when I try to set the weight
of an edge using the graph's setEdgeWeight method, I get an 
ClassCastException: edu.mit.jwi.item.Pointer (that is the class that
implements the IPointer interface).
Looking through the source code, I found that it tries to cast my edge to
a DefaultWeigtedEdge. I don't see the reason for that. Should my edge
class extend DefaultWeightedEdge? I can't find that in the (java)docs, nor
on the wiki.

Thanks in advance,

Maarten Th. Mulders

PS. Please excuse my last email, it was send accidentally send without
contents.

Yes, either your edge class needs to extend DefaultWeightedEdge, or your 
graph implementation needs to override setEdgeWeight.

JVS

Maarten Th. Mulders wrote:
> Hi all,
> 
> As I am trying to work with weighted graphs, I've come across a problem I
> don't understand.
> My weighted graph contains vertices of type ISynsetID and edges of
> IPointer. The former gives no problems, but when I try to set the weight
> of an edge using the graph's setEdgeWeight method, I get an 
> ClassCastException: edu.mit.jwi.item.Pointer (that is the class that
> implements the IPointer interface).
> Looking through the source code, I found that it tries to cast my edge to
> a DefaultWeigtedEdge. I don't see the reason for that. Should my edge
> class extend DefaultWeightedEdge? I can't find that in the (java)docs, nor
> on the wiki.
> 
> Thanks in advance,
> 
> Maarten Th. Mulders
> 
> PS. Please excuse my last email, it was send accidentally send without
> contents.
> 
> 
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my graph class:
public class GRFGraph extends DefaultDirectedWeightedGraph<GRFNode, GRFEdge>

my Edge class:
public class GRFEdge extends DefaultWeightedEdge

following method doesn't work anymore, it returns null.
GRFNode srcNode = graph.getEdgeTarget(new GRFEdge(1));

when my GRFEdge doesnt extend DefaultWeightedEdge it works fine. It will
return the node.

What is wrong with this call?

FYI:
in my GRFEdge class I override getWeight method already.

@Override
public double getWeight() {
        return weight;
} 
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The default edge implementations are optimized to be "intrusive"; that 
is, they contain direct references to their vertices.

When the graph sees an edge class that extends a default edge, it 
assumes that it can use these references rather than maintaining the 
edge/vertex association indirectly via a HashMap (which is more expensive).

In your case, you are creating a new edge on the fly, so when the graph 
examines it, the references are null.  When you use a non-default 
implementation everything works because then the new GRFEdge probably 
Object.equals some existing edge in the graph.

JVS

Fabian K wrote:
> my graph class:
> public class GRFGraph extends DefaultDirectedWeightedGraph<GRFNode, GRFEdge>
> 
> my Edge class:
> public class GRFEdge extends DefaultWeightedEdge
> 
> following method doesn't work anymore, it returns null.
> GRFNode srcNode = graph.getEdgeTarget(new GRFEdge(1));
> 
> when my GRFEdge doesnt extend DefaultWeightedEdge it works fine. It will
> return the node.
> 
> What is wrong with this call?
> 
> FYI:
> in my GRFEdge class I override getWeight method already.
> 
> @Override
> public double getWeight() {
>         return weight;
> } 

my graph class:
public class GRFGraph extends DefaultDirectedWeightedGraph<GRFNode, GRFEdge>

my Edge class:
public class GRFEdge extends DefaultWeightedEdge

following method doesn't work anymore, it returns null.
GRFNode srcNode = graph.getEdgeTarget(new GRFEdge(1));

when my GRFEdge doesnt extend DefaultWeightedEdge it works fine. It will
return the node.

What is wrong with this call?

FYI:
in my GRFEdge class I override getWeight method already.

@Override
public double getWeight() {
	return weight;
}
-- 
View this message in context: http://jgrapht-users.107614.n3.nabble.com/Weighted-graphs-tp107885p890828.html
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