Network Model: Class casting, NPE, method design

Question

Hello, all!
I have several specific questions. I have an agent-based network model which has no current (visible) errors. I have several conceptual problems with it, nonetheless. I'm going to list the problems with the associated code, and would very much appreciate any suggestions and help that can be offered.
(1) This is in the secondary class called Node.java. Though I've never really used strings, I think I'm correctly using them in these two methods. In them, I take a 5-digit integer (culture, a random number from 10000-99999), attempt to convert it to a string, compare it to another agent's culture (digit by digit, with the int variable "similarity" increasing by 1 each time a matching digit is found), and calculate a double variable "culturalSimilarity" which will give me a percentage of .00, .20, .40, .60, .80, or 1.00 if none, some, or all of the digits match. If my predetermined value for culturalSimilarity is reached (probably 40%, and meaning that out of the 5 digit string each agent has, 2 digits match), I want the agent to change one of its non-matching digits to match one of those of the other agent. I don't actually know how to design the second method, and just have pseudocode there. First, does the first method work well, or are there things in there that I should change to improve it/make it better code? Second, how the heck do I design the second method? I don't even know where to start...
  public void howCloselyDoOurCulturesMatch() {
       String stringCulture = String.valueOf(culture);
       int similarity = 0;
       for( int i = 0; i < stringCulture.length(); ++i ) {
            if( stringCulture.equals( stringCulture.substring( i, i+1 ) ) ) {
                 similarity++;
       if ( (similarity/5) >= culturalSimilarity) {
            exchangeCulture();
  public void exchangeCulture() {
       //make one of my non-matching digits match one of his.
(2) This is in the primary class called Model.java. I am getting a NPE in the main model in the buildModel() method at this line: "Node node = (Node) nodeList.get(i);" I think it has to do with my class casting. My casting is a mess, but I'm not sure how to fix it. Here are the three methods in which I create a network with nodes in it.
  public List makeNetwork () {
       System.out.println("Model.createWattsStrogatzNetwork() beginning.");
       List networkList = (List) NetworkFactory.createWattsStrogatzNetwork( numAgents,
              connectRadius, pRewiring, Node.class, Edge.class);
       System.out.println("Model.makeNetwork() finished.");
       return networkList;
  public void sortNetwork() {
          Vector nodeList = new Vector();
          System.out.println("==> created variables in the step method");
          for (int i = 0; i < networkList.size(); i++) {
               Object o = networkList.get(i);
               if (o instanceof Edge){
                    edgeList.add(o);
               System.out.println("==> edge added to edgeList");
               else if (o instanceof Node){
                    nodeList.add(o);
               System.out.println("==> node added to nodeList");
       //HELP maybe convert nodeList and edgeList back to ArrayLists with Nodes and Edges in them, not
       //Vectors with objects in them.
  private void buildModel () {
       System.out.println("Model.buildModel() beginning.");
       networkList = makeNetwork();//IS THIS A DUPLICATE?  SHOULD THIS BE HERE?
       //HELP this is defined in two different places.  nodeList needs to be only the Nodes.
       for (int i = 0; i < numAgents; i++) {
            Node node = (Node) nodeList.get(i);//HERE IS THE NULL POINTER EXCEPTION
            int x = Random.uniform.nextIntFromTo (0, worldXSize - 1);
            int y = Random.uniform.nextIntFromTo (0, worldYSize - 1);
            int nodeID = node.getID();
            node.setX(x);
            node.setY(y);
            int culture = node.getCulture();
            node.setNodeLabel ("Culture - " + culture);
            node.setBorderColor (Color.magenta);
            node.setBorderWidth (4);
            System.out.println("Model.buildModel() finished.");
  }So first, "networkList" is a List full of different kinds of information. I try to sort out the Nodes in that list with the Vector "nodeList", into which I add Objects that WERE Nodes and apparently aren't anymore. There is a comment under the method sortNetwork() saying I need the nodes back in an ArrayList, but I'm willing to go with any kind of list that ensures that the Nodes still possess the information they had when they were in networkList, specifically the edges that go into and out of them. I don't know how much information I'm stripping away from the Nodes by calling them Objects and putting them in a Vector. Any suggestions are extremely welcome.

Answer 1

I think I may understand what part of the NPE problem is, but I don't know how to fix it. The problem seems to be with the variable "networkList". It stores a lot of information from the makeWattsStrogatzNetwork method. When I use this for loop:
          for (int i = 0; i < networkList.size(); i++) {
               Object o = networkList.get(i);
               if (o instanceof Edge){
                    edgeList.add(o);
               System.out.println("==> edge added to edgeList");
               else if (o instanceof Node){
                    nodeList.add(o);
               System.out.println("==> node added to nodeList");
          }I get the NPE at the first line. My problem is that I have to iterate through networkList and all the different kinds of information it possesses, and pull all the nodes out into a Vector called nodeList. How do I do that? The big disconnect in my whole model is right here--networkList contains variables, Nodes, Edges, and parameters. I just want to suck the Nodes out of the list. What am I doing wrong?