code: @Override
  	public void addEdge(Edge e) {
  		
  		addDirectionalEdge(e);
  		
  		if (e.isBidirectional())
  			addDirectionalEdge(new Edge(e.getToNodeId(), e.getFromNodeId(), e.getWeight()));
  	}
docs: Add a new edge into the graph.
  @param e the edge that will be added into the graph.