Re: [jgrapht-users] getEdgeWeight in weighted Graph

[Georg H. <geo...@go...>]

i strongly agree with your suggestion.
 i already had the problem by myself, but forgot to write a pull request
afterwards ....
It's quiet horrible to find bugs, if you dont know about the current
behavior.


On 21 March 2014 19:56, Joris Kinable <de...@gm...> wrote:

> Dear,
>
> In the latest version of jgrapht (and perhaps also in other versions), the
> getEdgeWeight(E e) function is implemented as follows:
>
> public double getEdgeWeight(E e)
>     {
>         if (e instanceof DefaultWeightedEdge) {
>             return ((DefaultWeightedEdge) e).getWeight();
>         } else {
>             return WeightedGraph.DEFAULT_EDGE_WEIGHT;
>         }
>     }
>
>
> If e==null, i.e. the edge does not exist, then this function will return
> DEFAULT_EDGE_WEIGHT. This is strange as often invoking the getEdgeWeight
> function on a non-existing edge is simply a bug.
>
> I would suggest to modify the above function to something like:
> public double getEdgeWeight(E e)
>     {
>         if (e instanceof DefaultWeightedEdge) {
>             return ((DefaultWeightedEdge) e).getWeight();
>         } else if(e==null){
>            throw new UnsupportedArgumentException("Edge cannot be null");
>         }else{
>             return WeightedGraph.DEFAULT_EDGE_WEIGHT;
>         }
>     }
>
> One common error would be something like:
> Edge e=graph.getEdge(i,j); //Edge (i,j) is not part of the graph, so
> e==null;
> cost += graph.getEdgeWeight(e); //Correct, does not invoke an exception
>
>
> At the very least, the javadoc for the getEdgeWeight function should
> mention the above pitfall by specify that invoking the getEdgeWeight
> function on null returns WeightedGraph.DEFAULT_EDGE_WEIGHT so it's the
> user's problem to check whether the edge is not equal to null.
>
> This is just a suggestion. If there is support for this change, I'll make
> a change request.
>
> br,
>
> Joris
>
>
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