Java: .equals() failing for sets (JGraphT)

Question

I can't figure out what's going wrong here. This test fails:

@Test
    public void testSimpleCase() {
        assertTrue(JGraphtUtilities.graphEquality(ChooseRootTest.generateSimpleCaseGraph(), ChooseRootTest.generateSimpleCaseGraph()));
    }

public static <V, E> boolean graphEquality(Graph<V, E> g0, Graph<V, E> g1) {

    boolean result = true;

    if (g0.edgeSet().equals(g1.edgeSet()) && g0.vertexSet().equals(g1.vertexSet())) {
        for (E e : g0.edgeSet()) {
            if (g0.getEdgeWeight(e) != g1.getEdgeWeight(e)) {
                result = false;
            }
        }
    }
    else {
        return false; //for the above test, this is what is returned
    }

    return result;
}

The debugger shows that the method decides that the two vertex sets and edge sets aren't equal, so it returns false. How is this possible?

Side note: I'm trying to write an equality check for JGraphT graphs. How is it possible that this hasn't been done already?

UPDATE: I think that DefaultWeightedEdge doesn't override equals, so that wouldn't work. I did a different way of checking that edges exist between all necessary vertices, and now it seems to work.

Answer 1

According to the JavaDoc DefaultWeightedEdge hasn't implemented equals() and hashCode() and thus uses the methods defined in java.lang.Object. This means that two DefaultWeightedEdge objects a and b with the same values will not return true from a.equals(b). That would only return true if a and b actually refer to the same object.

You need to use an edge implementation class that implements .equals() and hashCode() to get useful results here.