code: protected Set<Integer> getNeighbors(int node) {
  
          Set<Integer> neighbors = new HashSet<Integer>();
          Set<DefaultEdge> edges = undirectedGraph.edgesOf(node);
          for (DefaultEdge edge : edges) {
              if (undirectedGraph.getEdgeSource(edge) != node) {
                  neighbors.add(undirectedGraph.getEdgeSource(edge));
              }
              if (undirectedGraph.getEdgeTarget(edge) != node) {
                  neighbors.add(undirectedGraph.getEdgeTarget(edge));
              }
          }
          return neighbors;
      }
docs: Get the neighbors of a given node.
  The category graph is treated as an undirected graph.
  @param node the reference node.
  @return The set of category nodes that are neighbors of this category.