ClassCastException : cant be cast to java.lang.Integer

Question

I know this has been asked a lot in stackoverflow but I could not find answers that work to my problem.

In the following code below, I cant print out each item in

Answer 1

the error lies here

  public void addEdgeForIndexing(int from, int to, int T) throws IllegalArgumentException, IllegalAccessException {   

            Edge e = new Edge(from,to,T);
            nodeIDs.add(e.from);
            nodeIDs.add(e.to);

            ArrayList tmp = null;
            if (edges.containsKey(e.from))
              tmp = (ArrayList) edges.get(e.from);
            else {
              tmp = new ArrayList();
              edges.put(e.from,tmp);
            }
            tmp.add(e);//adding an edge to tmp

later in the code you get the ArrayList out of the Map as ArrayList but it an ArrayList containing Edge try to change

tmp = new ArrayList();

to

tmp = new ArrayList();

you should get a compilation error when adding an Edge to it