Something like 'contains any' for Java set?

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 over the sets? The Set library has contains(object) and containsAll(collection), but not containsAny(collection).

Wouldn't Collections.disjoint(A, B) work? From the documentation:

Returns true if the two specified collections have no elements in common.

Thus, the method returns false if the collections contains any common elements.

Stream::anyMatch

Since Java 8 you could use Stream::anyMatch.

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

Apache Commons has a method CollectionUtils.containsAny().

A good way to implement containsAny for sets is using the Guava Sets.intersection().

containsAny would return a boolean, so the call looks like:

Sets.intersection(set1, set2).isEmpty()

This returns true iff the sets are disjoint, otherwise false. The time complexity of this is likely slightly better than retainAll because you dont have to do any cloning to avoid modifying your original set.

I use org.apache.commons.collections.CollectionUtils

CollectionUtils.containsAny(someCollection1, someCollection2)

That is All! Returns true if at least one element is in both collections.

Simple to use, and the name of the function is more suggestive.