code: public static <T> Set<T> difference(Set<T> setA, Set<T> setB) {
          Set<T> difference = new HashSet<T>(setA);
          difference.removeAll(setB);
          return difference;
      }
docs: This method finds the difference between set A and set B i.e. set A minus set B
  @param setA set A
  @param setB set B
  @param <T> type
  @return a new set containing the difference