Invalid casts - Object and Integer

Question

OK, I have got myself confused with casts. I have written this code, which I have [bold]SUBMITTED[bold] to University (so if you change it you are not helping me cheat...) . It doesn't compile and I am out of ideas why. The problem is the last method returnEvenNumbers(). Please could someone help me learn how this should be used by turning this into running code.
* Filename: RandomNumberArray.java
* Author: Steven Lane
* Email: [email protected]
* Created on 17 February 2002, 17:53
* Course: KIT eLearning, MSc in IT, University of Liverpool, UK
*         MSC-JV0020110-03
* Purpose: This class creates an uncostrained array of length L passed as int on instantiation.
*          The array is populated with (pseudo) random numbers.
*          Methods contain a filter for even numbers, which is pushed onto a stack.
* Version: 0.2
//package com.thinkcorporation.week6;
// ------------------- Import Packages -------------------
import java.util.*;
// ------------------- Class Heading -------------------
public class RandomNumberArray extends java.lang.Object {
    // ------------------- Field Defintions -------------------
   private Stack stkEvenNumbers = new Stack();
    private int [] rndNoArray;
    //private int [] evenNoArray;
    private Integer evenNoArray[];
    // ------------------- Constructors -----------------------
    public RandomNumberArray(int length) {
        rndNoArray = new int [length];
        populateRndNoArray();
    //------------------- Methods -----------------------------
    private void populateRndNoArray() {
        Random rnd = new Random();
        for(int counter = 0; counter < rndNoArray.length; counter++) {
            rndNoArray[counter] = rnd.nextInt();
    public void evenNumberFilter() {
        for(int counter = 0; counter < rndNoArray.length; counter++) {
            if (rndNoArray[counter]%2 == 0)
                stkEvenNumbers.push(new Integer(rndNoArray[counter]));
    public int [] returnEvenNumbers() {
        if (!stkEvenNumbers.empty()) {
            evenNoArray = new Integer [stkEvenNumbers.size()];
            evenNoArray = (Integer)stkEvenNumbers.toArray();
        return evenNoArray;
}You help is much appreciated.

Answer 1

The root of the problem is a difference between primitive types and objects. The Stack.toArray() method returns an array of Objects (Object[]), which you can cast to an array of Integer objects (Integer[]):
evenNoArray = (Integer[])stkEvenNumbers.toArray();However, your return type for that method is int[] - a primitive types, not objects. Meaning that you either have to step through the array and build an array of ints (using Integer.intValue()), or you have to change the return type of your method.