list - 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 below example:

Suppose I have 2 ArrayList:

ArrayList A has object a, object b and object c
ArrayList B has object d, object e

Then the output should be 6 new ArrayList with these combinations:

Combination 1 object a and object d,
Combination 2 object a and object e,
Combination 3 object b and object d,
Combination 4 object b and object e,
Combination 5 object c and object d,
Combination 6 object c and object e,

Can anyone help me?

Answer 1

Guava 19+

Lists.cartesianProduct(List...)

E.g.:

List<Object> list1 = Arrays.asList("a", "b", "c");
List<Object> list2 = Arrays.asList("d", "e");
System.out.println(Lists.cartesianProduct(list1, list2));

Output:

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