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

private HashMap<Integer, ArrayList<Integer>>  edges;

// ...later

Edge e = new Edge(from,to,T);

// ...later

else {
    tmp = new ArrayList();
    edges.put(e.from,tmp);
}
tmp.add(e);

Ultimately, this is a classic example of why raw types are bad. You've got an ArrayList<Integer> and you put Edges in it.

Unfortunately, I don't know how to tell you how to fix it since I don't understand what you're trying to do.

Answer 2

You declare:

int from;
int to;
int type;

and you should declare them as Integers instead:

Integer from;
Integer to;
Integer type;

because later on you're doing:

this.from = new Integer(from);

etc.

A better option would be to change the assignment to:

this.from = from;

which would also solve this error since you would be assigning an int to an int. Is there a purpose you're using new Integer() ? because if not - I would suggest removing it - it's slower (performance-wise) comparing to the primitive int.

Bottom line: stay consistent and either use int throughout the code, or Integer - try not to mix them unless it's really required.

Answer 3

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<Integer>();

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

Answer 4

    public ArrayList<Integer> getOutEdgesToP(int id) {
if (!edges.containsKey(id)) {
    return null;
}
System.out.println(edges.get(id));
ArrayList<Integer> a = edges.get(id);
System.out.println("Arraylist a: " + a); // if i print using this its
                     // okay. but i cant get each
                     // item in this ArrayList like
                     // below
for (Object item : a) { // the error of classcastexception is here
    System.out.println(item);
}

return a;
}

This should work. I don't have a lot of time to search for an explanation.