问题

How to add two edges having the same label but different endpoints?

For example, I want to add two edges having the same label 'label1', one from vertex v-1 to vertex v-2 and the other one from vertex v-2 to v-3.

Part of the code would be:

g.addEdge("label1","v-1","v-2");
g.addEdge("label1","v-2","v-3");

But JUNG does not allow to add two edges with the same label. It gives an error:

edge label1 already exists in this graph with endpoints [v-1, v-2] and cannot be added with endpoints [v-2, v-3]

How can I add two edges having the same label?

Thanks.

Edit:

I just read that there is a way to assign a weight value to an edge, that is by using EdgeWeightLabeller, but these weight values should be integers. So it does not seem to solve the problem.

回答1:

Labels are not required to be the toString() of the edges; that's just the default. Take a look at PluggableRendererContext to see how to supply a Transformer that provides a property for each element of the graph.

I'd also check out the section in the JUNG 2 manual (on the wiki) that talks about user data: http://sourceforge.net/apps/trac/jung/wiki/JUNGManual#UserData

回答2:

When I have this problem, I make my label String (your is already a String) and make its value like this: "ID_OF_FIRST_VERTEX:ID_OF_SECOND_VERTEX:EDGE_VALUE". Then, to display just a value, I do use transformation. Its simple, it just takes the edge_value from name of edge.

In this sample I use a separator ":".

VisualizationViewer vv = new VisualizationViewer(layout, dim);
//other operations
vv.getRenderContext().setEdgeLabelTransformer(new Transformer<String, String>() {
    @Override
    public String transform(String c) {
        return StringUtils.substringAfterLast(c, ":");
    }
});

Of course you dont have to use StringUtils from Apache Commons, a normal String.subString will work here as well.

Hope it helps.

回答3:

Here is an MCVE example.

package stackoverflow;

import javax.swing.JFrame;
import org.apache.commons.collections15.Transformer;
import edu.uci.ics.jung.algorithms.layout.FRLayout;
import edu.uci.ics.jung.graph.DirectedSparseMultigraph;
import edu.uci.ics.jung.graph.Graph;
import edu.uci.ics.jung.visualization.VisualizationViewer;


public class JungNetwork {

public static Graph<String, String> getGraph() 
{
    Graph<String, String> g = new DirectedSparseMultigraph<String, String>();

    g.addVertex("v1");
    g.addVertex("v2");
    g.addVertex("v3");
    g.addEdge("label1", "v1", "v2");
    g.addEdge("label2", "v2", "v3");
    g.addEdge("label3", "v3", "v1");
    return g;
}


public static void main(String[] args) 
{
    JFrame f = new JFrame();
    final Graph<String, String> g = getGraph();
    VisualizationViewer<String, String> vv =    new VisualizationViewer<String, String>(new FRLayout<String, String>(g));

    final Transformer <String, String> edgeLabel = new Transformer<String, String>(){

        @Override
        public String transform(String edge) {
            // TODO Auto-generated method stub
            if (edge.equals("label1")|| edge.equals("label2")){
                return "label1";
            }else
            return "label3";
        }

    };


    vv.getRenderContext().setLabelOffset(15);
    vv.getRenderContext().setEdgeLabelTransformer(edgeLabel);

    f.getContentPane().add(vv);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.pack();
    f.setVisible(true);
}


}

The Result: