intersection method

Set<E> intersection (Set<Object> other)

Returns a new set which is the intersection between this set and other.

That is, the returned set contains all the elements of this Set that are also elements of other according to other.contains.

Implementation 

Set<E> intersection(Set<Object> other) {
  Set<E> result = toSet();
  for (E element in this) {
    if (!other.contains(element)) result.remove(element);
  }
  return result;
}