Object differentiation - graph

Question

I'm creating a graph with nodes (with integer value) and edges (source, destination and weight) by reading a file with the format
1 51 1
1 72 2
1 77 1
etc.
Set<Node> nodes = new HashSet<Node>(); //a set of the nodes of a graph
ArrayList<Node> nodeList = new ArrayList<Node>();
ArrayList<Edge> edgeList = new ArrayList<Edge>();
...
Node node1=new Node(Integer.parseInt(temprelation[0]));
Node node2=new Node(Integer.parseInt(temprelation[1]));
nodes.add(node1);
nodes.add(node2);
Edge edge = new Edge(node1, node2, Integer.parseInt(temprelation[2]));
edgeList.add(edge);
}
The class Node has also a field "number of neighbors", and I wanted to go through all the edges and increment the number of neighbors whenever either source or destinatio appears.
for (int edge=0; edge<graph.getEdges().size(); edge++){
graph.getEdges().get(edge).getSource().neighborUp();
graph.getEdges().get(edge).getDestination().neighborUp();
}
Strangely enough, although the objects seem to be the same (I checked it with equals), the counter does not go up. E.g., for 1, it goes up once with the first edge, but does not go up when I try to increment it when the second edge is concerned. When considering the second edge before incrementing, it somehow shows the number of neighbors is 0, although I incremented the number of neighbors of the first node already in the first edge. So if I did printouts of counters before and after incrementation I always get 0 1 0 1 as if some other objects were concerned.

Answer 1

I assume that you use Java.
The problem is with creation of the graph, every time when you create an edge you create new objects for nodes:
Node node1=new Node(Integer.parseInt(temprelation[0]));
Node node2=new Node(Integer.parseInt(temprelation[1]));
The set contains only one copy for every Integer, but your edges contain different instancies.
To solve it you can create a map of all already parsed nodes and at every iteration instead of creating object from Integer, check if you have already created the object from Integer:
//one global object
Map<Integer,Node> map = new HashMap<Integer,Node> ();
...
Integer val = Integer.parseInt(temprelation[0]);
if (map.get(val)==null) {
map.put(val, new Node(val));
}
Node node1 = map.get(val);
val = Integer.parseInt(temprelation[1]);
if (map.get(val)==null) {
map.put(val, new Node(val));
}
Node node2 = map.get(val);