Method intersection

corpus/java/training/guava/collect/Sets.java:658–689

Returns an unmodifiable view of the intersection of two sets. The returned set contains all elements that are contained by both backing sets. The iteration order of the returned set matches that of set1. Results are undefined if set1 and set2 are sets based on diff

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

   * <p>This is unfortunate, but should come up only very rarely.
   */
  public static <E> SetView<E> intersection(final Set<E> set1, final Set<?> set2) {
    checkNotNull(set1, "set1");
    checkNotNull(set2, "set2");

    final Predicate<Object> inSet2 = Predicates.in(set2);
    return new SetView<E>() {
      @Override
      public Iterator<E> iterator() {
        return Iterators.filter(set1.iterator(), inSet2);
      }

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

      @Override
      public boolean isEmpty() {
        return !iterator().hasNext();
      }

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

      @Override
      public boolean containsAll(Collection<?> collection) {
        return set1.containsAll(collection) && set2.containsAll(collection);
      }
    };
  }

  /**
   * Returns an unmodifiable <b>view</b> of the difference of two sets. The