How do I generate a Cartesian product in Java?

Question

I have a number of ArrayList with each ArrayList having objects and each one can have different length. I need to generate permutation like in the

Answer 1

With Java8 streams

    List a = Arrays.asList("a", "b", "c");
    List b = Arrays.asList("d", "e");
    String[][] AB = a.stream().flatMap(ai -> b.stream().map(bi -> new String[] { ai, bi })).toArray(String[][]::new);
    System.out.println(Arrays.deepToString(AB));

output

    [[a, d], [a, e], [b, d], [b, e], [c, d], [c, e]]

To get as List

    List> ll = a.stream().flatMap(ai -> b.stream().map(bi -> new ArrayList<>(Arrays.asList(ai, bi)))).collect(Collectors.toList());