code: public void addNode(Node n) {
  		try {
  			structure.addNode(n);
  			for (NodeListener listener : nodeListeners)
  				listener.onInsert(n);
  		} catch (DuplicatedNodeException e) {
  			duplicatedNodesCounter++;
  		}
  	}
docs: Adds a new node to the graph, given the Node object. If a node already
  exists with an id equal to the given node, a DuplicatedNodeException is thrown.
  
  @param n the new node to be added to the graph.