Something like 'contains any' for Java set?

Question

I have two sets, A and B, of the same type.

I have to find if A contains any element from the set B.

What would be the best way to do that without iterating

Answer 1

I would recommend creating a HashMap from set A, and then iterating through set B and checking if any element of B is in A. This would run in O(|A|+|B|) time (as there would be no collisions), whereas retainAll(Collection<?> c) must run in O(|A|*|B|) time.

Answer 2

You can use retainAll method and get the intersection of your two sets.

Answer 3

Stream::anyMatch

Since Java 8 you could use Stream::anyMatch.

setA.stream().anyMatch(setB::contains)