Java Jung Object Instantiation

Question

I am trying to construct the following from the Java Jung Graph Package: EdmondsKarp Object

EdmondsKarpMaxFlow<MyNode, MyLink> alg = new EdmondsKarpMaxFlow<MyNode, MyLink>(g, n2, n5, capTransformer, edgeFlowMap, flowEdgeFactory);

I have no idea why I have an error, here is the error message from NetBeans:
reason: actual argument org.apache.commons.collections15.Transformer<selfsimilarity.MyLink,java.lang.Double> cannot be converted to org.apache.commons.collections15.Transformer<selfsimilarity.MyLink,java.lang.Number> by method invocation conversion.

I am essentially following a tutorial.

The EdmondsKarpMaxFlow instantiation is at the bottom of the constructor. AFter the constructor I give the code for all parameters to the EdmondsKarp object. These parameters are the graph, the source and sink nodes, the capacity transformer, the map, and the edge factory.

public GraphAlgTests()
    {
        g = new DirectedSparseMultigraph<MyNode, MyLink>();
        // Create some MyNode objects to use as vertices
        MyNode n1 = new MyNode(1); MyNode n2 = new MyNode(2); MyNode n3 = new MyNode(3);  
        MyNode n4 = new MyNode(4); MyNode n5 = new MyNode(5); 
        // Add some directed edges along with the vertices to the graph
        g.addEdge(new MyLink(2.0, 48),n1, n2, EdgeType.DIRECTED); // This method
        g.addEdge(new MyLink(2.0, 48),n2, n3, EdgeType.DIRECTED);
        g.addEdge(new MyLink(3.0, 192), n3, n5, EdgeType.DIRECTED); 
        g.addEdge(new MyLink(2.0, 48), n5, n4, EdgeType.DIRECTED); // or we can use
        g.addEdge(new MyLink(2.0, 48), n4, n2); // In a directed graph the
        g.addEdge(new MyLink(2.0, 48), n3, n1); // first node is the source 
        g.addEdge(new MyLink(10.0, 48), n2, n5);// and the second the destination

        EdmondsKarpMaxFlow<MyNode, MyLink> alg = new EdmondsKarpMaxFlow<MyNode, MyLink>(g, n2, n5, capTransformer, edgeFlowMap, flowEdgeFactory);
    }

public class MyNode 
{
    private int id; // good coding practice would have this as private
    public MyNode(int id) 
    {
        this.id = id;
    }
    public String toString() 
    {                        // Always a good idea for debuging
        return "v"+id;       // JUNG2 makes good use of these.
    }        
}


public class MyLink 
{
    double capacity; // should be private 
    double weight;   // should be private for good practice
    int id;
    int edgeCount = 0;

    public MyLink(double weight, double capacity) 
    {
        this.id = edgeCount++; 
        this.weight = weight;
        this.capacity = capacity;
    } 
    public String toString() 
    { // Always good for debugging
        return "E"+id;
    }
}

   Transformer<MyLink, Double> capTransformer = new Transformer<MyLink, Double>()
   //INFO: Gives the capacity of an edge, denoted here as a "link"
   {
       @Override
       public Double transform(MyLink link)
       {
           return link.capacity;
       }
   };

   Map<MyLink, Double> edgeFlowMap = new HashMap<MyLink, Double>();
   Factory<MyLink> flowEdgeFactory = new Factory<MyLink>()
   {
        @Override
        public MyLink create()
        {
            return new MyLink(1.0, 1.0);
        }
   };

If there is anything else that could help, let me know! Thanks for all the help!

Answer 1

It's telling you exactly what the Javadocs for that constructor tell you:

public EdmondsKarpMaxFlow(DirectedGraph<V,E> directedGraph,
                          V source,
                          V sink,
                          org.apache.commons.collections15.Transformer<E,Number> edgeCapacityTransformer,
                          Map<E,Number> edgeFlowMap,
                          org.apache.commons.collections15.Factory<E> edgeFactory)

Your Transformer is <MyLink, Double> when it needs to be <MyLink, Number> (and your transform() method inside it needs to be defined to return a Number)

This was probably changed at some point in the API and the tutorial you're using is out of date. More than likely the API is now calling doubleValue() on the Number object you will return.

It would appear the same goes for your edgeFlowMap as well.