[jgrapht-users] DirectedNeighborIndex + ListenableDirectedGraph = bug?

[Konstantin_R <rub...@us...>]

Hello jgrapht!

I tried to ask this question at https://github.com/jgrapht/jgrapht/issues ,
but maybe it was the wrong place for it. 
Could you please help me with the following?

I think I came across a bug that affects a general graph behavior.

When using ListenableDirectedGraph one can add a listener using method
'addGraphListener()'.
When using DirectedNeighborIndex a listenable graph should be passed in the
DirectedNeighborIndex's contructor as a parameter.
According to the DirectedNeighborIndex's spec "If it [DirectedNeighborIndex]
is added as a listener to a graph other than the one it indexes, results are
undefined." 
Does it mean that the behavior of the DirectedNeighborIndex becomes
undefined or also the behavior of the graphs concerned as well?
I suppose, that graphs concerned shouldn't be affected in this situation. Is
it true?

In reality the behavior of graph changes and
java.lang.IllegalArgumentException is thrown 
at org.jgrapht.graph.AbstractGraph.assertVertexExist() when trying to add a
new edge in the graph.

The following JUnit test highlights the problem:

public void testListenableDirectedGraph() throws Exception {
        ListenableDirectedGraph<String, DefaultEdge> listenDG = new
ListenableDirectedGraph<String, DefaultEdge>(
                DefaultEdge.class);
        String vertex1 = "v1";
        listenDG.addVertex(vertex1);
        String vertex2 = "v2";
        listenDG.addVertex(vertex2);
        listenDG.addEdge(vertex1, vertex2);

        ListenableDirectedGraph<String, DefaultEdge> listenDG2 = new
ListenableDirectedGraph<String, DefaultEdge>(
                DefaultEdge.class);
        DirectedNeighborIndex<String, DefaultEdge> dni = new
DirectedNeighborIndex<String, DefaultEdge>(
                listenDG2);

        listenDG.addGraphListener(dni);

        String vertex3 = "v3";
        listenDG.addVertex(vertex3);
        listenDG.addEdge(vertex3, vertex1); // throws
IllegalArgumentException exception
    }

In the jgrapht mailing list there's a bug which looks related, 
although I cannot be sure:
http://jgrapht-users.107614.n3.nabble.com/Re-Bug-in-the-induced-subgraphs-Patch-and-JUnit-test-td1605888.html

Could you please confirm if this is a problem?
As a possible solution, is it possible to have a check in the
'addGraphListener()' to avoid such behavior?

Thanks,
Konstantin




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