unfiltered.add("zzz");
                unfiltered.add("abc");
                return Sets.filter(
                    Sets.filter(unfiltered, Collections2Test.LENGTH_1),
                    Collections2Test.NOT_YYY_ZZZ);
              }
            })
        .named("Sets.filter, filtered input")
        .withFeatures(
            CollectionFeature.SUPPORTS_ADD,

    Iterator<String> filtered = Iterators.filter(unfiltered, Predicates.alwaysFalse());
    List<String> expected = Collections.emptyList();
    List<String> actual = Lists.newArrayList(filtered);
    assertEquals(expected, actual);
  }

  public void testFilterMatchAll() {
    Iterator<String> unfiltered = Lists.newArrayList("foo", "bar").iterator();
    Iterator<String> filtered = Iterators.filter(unfiltered, Predicates.alwaysTrue());

    return CollectCollectors.toImmutableSortedMap(
        comparator, keyFunction, valueFunction, mergeFunction);
  }

  /*
   * TODO(kevinb): Confirm that ImmutableSortedMap is faster to construct and
   * uses less memory than TreeMap; then say so in the class Javadoc.
   */
  private static final Comparator<?> NATURAL_ORDER = Ordering.natural();

   * java.util.stream.Stream#filter}. This method is not being deprecated, but we gently encourage
   * you to migrate to streams.
   */
  // TODO(kevinb): how to omit that last sentence when building GWT javadoc?
  public static <E extends @Nullable Object> Set<E> filter(
      Set<E> unfiltered, Predicate<? super E> predicate) {
    if (unfiltered instanceof SortedSet) {
      return filter((SortedSet<E>) unfiltered, predicate);

   * query than the original; your mileage may vary. Precomputation takes time and is likely to be
   * worthwhile only if the precomputed matcher is queried many thousands of times.
   *
   * <p>This method has no effect (returns {@code this}) when called in GWT: it's unclear whether a
   * precomputed matcher is faster, but it certainly consumes more memory, which doesn't seem like a

@ElementTypesAreNonnullByDefault
public abstract class AbstractFuture<V extends @Nullable Object> extends InternalFutureFailureAccess
    implements ListenableFuture<V> {
  // NOTE: Whenever both tests are cheap and functional, it's faster to use &, | instead of &&, ||

  static final boolean GENERATE_CANCELLATION_CAUSES;

  static {
    // System.getProperty may throw if the security policy does not permit access.
    boolean generateCancellationCauses;

    return CollectCollectors.toImmutableSortedMap(
        comparator, keyFunction, valueFunction, mergeFunction);
  }

  /*
   * TODO(kevinb): Confirm that ImmutableSortedMap is faster to construct and
   * uses less memory than TreeMap; then say so in the class Javadoc.
   */
  private static final Comparator<?> NATURAL_ORDER = Ordering.natural();

   * underlying multimap.
   *
   * <p>The returned multimap isn't threadsafe or serializable, even if {@code unfiltered} is.
   *
   * <p>Many of the filtered multimap's methods, such as {@code size()}, iterate across every
   * key/value mapping in the underlying multimap and determine which satisfy the filter. When a

    Iterator<String> filtered = Iterators.filter(unfiltered, Predicates.alwaysFalse());
    List<String> expected = Collections.emptyList();
    List<String> actual = Lists.newArrayList(filtered);
    assertEquals(expected, actual);
  }

  public void testFilterMatchAll() {
    Iterator<String> unfiltered = Lists.newArrayList("foo", "bar").iterator();
    Iterator<String> filtered = Iterators.filter(unfiltered, Predicates.alwaysTrue());

   */
  @SuppressWarnings("unchecked") // can cast to <T> because non-Ts are removed
  @GwtIncompatible // Class.isInstance
  public static <T> UnmodifiableIterator<T> filter(Iterator<?> unfiltered, Class<T> desiredType) {
    return (UnmodifiableIterator<T>) filter(unfiltered, instanceOf(desiredType));
  }

  /**
   * Returns {@code true} if one or more elements returned by {@code iterator} satisfy the given
   * predicate.
   */