product.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class arraycalc {
    public static void main(String[] args) {
        List<List<Object>> n = new ArrayList();
        n.add(Arrays.asList("A", "B", "C"));
        n.add(Arrays.asList(4, 5));
        n.add(Arrays.asList(0));
        System.out.println(product(n));
    }

    public static <T> List<List<T>> product(List<List<T>> b) {
        List<List<T>> result = new ArrayList<List<T>>();
        List<List<T>> xx;
        for (int i = 0; i < b.get(0).size(); i++) {
            final int j = i;
            if (b.size() > 1) {
                xx = product(b.stream().skip(1).collect(Collectors.toList()));
                xx = xx.stream().map(x ->
                        Stream.concat(Stream.of(b.get(0).get(j)), x.stream()).collect(Collectors.toList())
                    ).collect(Collectors.toList());
            } else {
                xx = Arrays.asList(Arrays.asList(b.get(0).get(i)));
            }
            result.addAll(xx);
        }
        return result;
    }
}

// OUTPUT
// [[A, 4, 0], [A, 5, 0], [B, 4, 0], [B, 5, 0], [C, 4, 0], [C, 5, 0]]