如何创建具有相同权重和相同源顶点的多个边？

Question

I'm using jgrapht and I'm having a problem here. As soon as I create two edges with the same weight from one source vertex, I end up having just one edge:

DirectedWeightedPseudograph<Object, Object> Grph1 = new DirectedWeightedPseudograph<>(Object.class);

    Grph1.addVertex("a");
    Grph1.addVertex("b");
    Grph1.addVertex("c");

    Grph1.addEdge("a", "b", "55");
    Grph1.addEdge("a", "c", "55");

I expect the output:

a--55-->b
a--55-->c

But the actual output:

a--55-->b
c

Answer 1

You are not creating two edges. You are only creating one edge, and this edge is "55" . Right: The string "55" is the edge in your example.

In order to create multiple edges with real weights (pun intended), you should declare your graph to have the right type, namely one that uses, for example, DefaultWeightedEdge as the edge type.

Then, when you add a new edge by calling addEdge , you receive the DefaultWeightedEdge instance. Using this instance, you can assign the weight to this edge, by calling setEdgeWeight .

Graph<String, DefaultWeightedEdge> g = new DirectedWeightedPseudograph<>(DefaultWeightedEdge.class);
g.addVertex("a");
g.addVertex("b");
g.addVertex("c");

DefaultWeightedEdge e0 = g.addEdge("a", "b");
g.setEdgeWeight(e0, 55.0);

DefaultWeightedEdge e1 = g.addEdge("a", "c");
g.setEdgeWeight(e1, 55.0);

System.out.println(g.edgeSet());

Answer 2

From the documentation:

adds the specified edge e to this graph if this graph contains no edge e2 such that e2.equals(e)

Object o1=Grph1.addEdge("a", "b", "55");
Object o2=Grph1.addEdge("a", "c", "55");
boolean test=o1.equals(o2); //this will return true

Instead of creating your graph with <Object,Object> , use something different, eg <String,DefaultWeightedEdge> as is done in the examples:

Graph<String,DefaultWeightedEdge> g=new DirectedWeightedPseudograph<>(DefaultWeightedEdge.class);
g.addVertex("a");
g.addVertex("b");
g.addVertex("c");

g.addEdge("a", "b", "55");
g.addEdge("a", "c", "55");