Labeled Edges

A common requirement for JGraphT applications is the need to associate a label with each edge. This can be accomplished efficiently via a custom edge class:

:[source code](http://code.jgrapht.org/raw/master/jgrapht-demo/src/main/java/org/jgrapht/demo/LabeledEdges.java?example=edgeclass)

JGraphT’s default graph and edge implementations take care of maintaining the connectivity information between vertices, so the custom edge subclass only needs to store the label. Since the custom edge class does not override equals/hashCode, each edge object is distinct from every other edge object (regardless of whether they share the same label). Consequently, labels do not have to be unique within the same graph.

As defined above, RelationshipEdge could be used in either a directed or undirected graph. In the example below, we apply it to a a backstabby form of non-symmetric friendship via a directed graph:

:[source code](http://code.jgrapht.org/raw/master/jgrapht-demo/src/main/java/org/jgrapht/demo/LabeledEdges.java?example=create)

Since the RelationshipEdge class does not have a default constructor, edges must be explicitly instantiated and added via addEdge(V,V,E) rather than implicitly instantiated via addEdge(V,V).

Once the graph has been populated, label information can be accessed during traversal:

:[source code](http://code.jgrapht.org/raw/master/jgrapht-demo/src/main/java/org/jgrapht/demo/LabeledEdges.java?example=print)

Given two vertices, an application can check the label on the edge between them by using getEdge(V,V):

:[source code](http://code.jgrapht.org/raw/master/jgrapht-demo/src/main/java/org/jgrapht/demo/LabeledEdges.java?example=isEnemyOf)

You can find the complete source code for this example at LabeledEdge.java