Determination of the Cartesian product using java.util.Stack

Question

To find the Cartesian product of multiple sets, I have implemented an algorithm, but its output is still incorrect.

The algorithm uses two stacks (stack1 and stack2) to store intermediate results.

Here my implementation:

java.util.ArrayList;
java.util.Stack;

public class CartesianProduct {

    int k;
    ArrayList<String[]> product = new ArrayList<String[]>();

    public CartesianProduct(ArrayList<String> input) {

        k = input.size();

        Stack<String[]> stack1 = new Stack<String[]>();
        Stack<String[]> stack2 = new Stack<String[]>();

        String[] tupel = new String[k];
        for (int l = 0; l < k; ++l) {
            tupel[l] = input.get(l);
        }
        stack1.push(tupel);
        System.out.println("push on 1: "+tupel[0]+" "+tupel[1]+" "+tupel[2]);

        for (int l = 0; l < k; ++l) {
        
            System.out.println();
            if (l % 2 == 0) {
                while (!stack1.empty()) {
                    String[] tupel1 = stack1.pop();
                    System.out.println("pop from 1: "+tupel1[0]+" "+tupel1[1]+" "+tupel1[2]);       

                    String[] indices = tupel1[l].split(",");
                    String[] tupel2 = tupel1;
                    
                    for (String index : indices) {
                        tupel2[l] = index;
                        stack2.push(tupel2);
                        System.out.println("push on 2: "+tupel2[0]+" "+tupel2[1]+" "+tupel2[2]);                    }
                }
            } else {
                while (!stack2.empty()) {
                    String[] tupel1 = stack2.pop();
                    System.out.println("pop from 2: "+tupel1[0]+" "+tupel1[1]+" "+tupel1[2]);       

                    String[] indices = tupel1[l].split(",");
                    String[] tupel2 = tupel1;
                    for (String index : indices) {
                        tupel2[l] = index;
                        stack1.push(tupel2);

                        System.out.println("push on 1: "+tupel2[0]+" "+tupel2[1]+" "+tupel2[2]);        
                    }
                }
            }
        }

        if (k % 2 == 0) {
            while (!stack1.isEmpty()) {
                product.add(stack1.pop());
            }
        } else {
            while (!stack2.isEmpty()) {
                product.add(stack2.pop());
            }
        }

    }

    public int getK() {
        return k;
    }

    public ArrayList<String[]> getProduct() {
        return product;
    }

    public static void main(String args[]) {

        ArrayList<String> set = new ArrayList<String>();

        set.add("k1,k2,k3");
        set.add("m1,m2");
        set.add("s1");

        CartesianProduct prod = new CartesianProduct(set);
        System.out.println("k: " + prod.getK());
        for (String[] tupel : prod.getProduct()) {
            System.out.println(tupel[0] + " " + tupel[1] + " " + tupel[2]);
        }
    }
}

In a first while loop I put results on stack2 with push, but when I want to get them back down from stack2 in a second while loop with pop, this doesn't seem to work correctly.

At the moment the algorithm for the given example still returns the following erroneous output: determination