Method difference

corpus/java/training/guava/collect/Sets.java:702–728

Returns an unmodifiable view of the difference of two sets. The returned set contains all elements that are contained by set1 and not contained by set2. set2 may also contain elements not present in set1; these are simply ignored. The iteration order of the ret

(final Set<E> set1, final Set<?> set2)

   * and the keySet of an {@code IdentityHashMap} all are).
   */
  public static <E> SetView<E> difference(final Set<E> set1, final Set<?> set2) {
    checkNotNull(set1, "set1");
    checkNotNull(set2, "set2");

    final Predicate<Object> notInSet2 = Predicates.not(Predicates.in(set2));
    return new SetView<E>() {
      @Override
      public Iterator<E> iterator() {
        return Iterators.filter(set1.iterator(), notInSet2);
      }

      @Override
      public int size() {
        return Iterators.size(iterator());
      }

      @Override
      public boolean isEmpty() {
        return set2.containsAll(set1);
      }

      @Override
      public boolean contains(Object element) {
        return set1.contains(element) && !set2.contains(element);
      }
    };
  }

  /**
   * Returns an unmodifiable <b>view</b> of the symmetric difference of two