Implementation of SmallWorldExample

Question

I am pretty confused on how to implement some JUNG classes. I am trying to create a graph with "KleinbergSmallWorldGenerator" but I am not really sure how to initialize properly.

My code:

Factory<? extends Graph<Integer, Integer>> graph_factory;
Factory<Integer> vertexFactory;
Factory<Integer> edgeFactory;

KleinbergSmallWorldGenerator<Integer,Integer> smallWorld;

public GraphView() {
    smallWorld = new KleinbergSmallWorldGenerator<Integer,Integer>(graph_factory, vertexFactory, edgeFactory, 20, 3) ;
    Graph2 = smallWorld.create();
}

I get "java.lang.NullPointerException" even if I do graph_factory.create();

Help me understand; Thanks!

Answer 1

Example:

static class GraphFactory implements Factory<Graph<Integer,String>> {
        public Graph<Integer,String> create() {
            return new SparseMultigraph<Integer,String>();
        }
    }

    static class VertexFactory implements Factory<Integer> {
        int a = 0;
        public Integer create() {
            return a++;
        }

    }
    static class EdgeFactory implements Factory<String> {
        char aa = 'a';
        public String create() {
            return Character.toString(aa++);
        }

    }

And then you call for example this

Graph<Integer, String>  Eppstein = new EppsteinPowerLawGenerator<Integer,String>(new GraphFactory(), new VertexFactory(), new EdgeFactory(), 100, 400, 100).create();