@SuppressWarnings("unchecked")
  private static <T extends @Nullable Object> ListenableFuture<? extends T>[] gwtCompatibleToArray(
      Iterable<? extends ListenableFuture<? extends T>> futures) {
    Collection<ListenableFuture<? extends T>> collection;
    if (futures instanceof Collection) {
      collection = (Collection<ListenableFuture<? extends T>>) futures;
    } else {
      collection = ImmutableList.copyOf(futures);

   *
   * @since 3.0
   */
  public static <E extends @Nullable Object> SetView<E> symmetricDifference(
      Set<? extends E> set1, Set<? extends E> set2) {
    checkNotNull(set1, "set1");
    checkNotNull(set2, "set2");

    return new SetView<E>() {
      @Override
      public UnmodifiableIterator<E> iterator() {
        Iterator<? extends E> itr1 = set1.iterator();

    }
    return String.copyValueOf(tmp);
  }

  // Fast matchers

  /** A matcher for which precomputation will not yield any significant benefit. */
  abstract static class FastMatcher extends CharMatcher {

    @Override
    public final CharMatcher precomputed() {
      return this;
    }

    @Override
    public CharMatcher negate() {
      return new NegatedFastMatcher(this);

    // ? extends Number
    assertAssignable(new TypeToken<List<N1>>() {}, new TypeToken<List<? extends Number>>() {});
    assertAssignable(new TypeToken<ArrayList<N1>>() {}, new TypeToken<List<? extends Number>>() {});
    assertAssignable(
        new TypeToken<List<? extends N11>>() {}, new TypeToken<List<? extends Number>>() {});
  }

  public <N1 extends Number, N2 extends Number, N11 extends N1>

    // ? extends Number
    assertAssignable(new TypeToken<List<N1>>() {}, new TypeToken<List<? extends Number>>() {});
    assertAssignable(new TypeToken<ArrayList<N1>>() {}, new TypeToken<List<? extends Number>>() {});
    assertAssignable(
        new TypeToken<List<? extends N11>>() {}, new TypeToken<List<? extends Number>>() {});
  }

  public <N1 extends Number, N2 extends Number, N11 extends N1>

  public static <
          T extends @Nullable Object,
          K extends @Nullable Object,
          V extends @Nullable Object,
          M extends Multimap<K, V>>
      Collector<T, ?, M> flatteningToMultimap(
          java.util.function.Function<? super T, ? extends K> keyFunction,
          java.util.function.Function<? super T, ? extends Stream<? extends V>> valueFunction,

   */
  public static <
          T extends @Nullable Object,
          K extends @Nullable Object,
          V extends @Nullable Object,
          M extends Multimap<K, V>>
      Collector<T, ?, M> flatteningToMultimap(
          java.util.function.Function<? super T, ? extends K> keyFunction,
          java.util.function.Function<? super T, ? extends Stream<? extends V>> valueFunction,

     * operation O(1).
     */

    private @Nullable Iterator<? extends Iterator<? extends T>> topMetaIterator;

    // Only becomes nonnull if we encounter nested concatenations.
    private @Nullable Deque<Iterator<? extends Iterator<? extends T>>> metaIterators;

    ConcatenatedIterator(Iterator<? extends Iterator<? extends T>> metaIterator) {
      iterator = emptyIterator();

     * @return a new instance of {@link ConcurrentHashMap}
     * @see ConcurrentHashMap#ConcurrentHashMap(Map)
     */
    public static <K, V> ConcurrentHashMap<K, V> newConcurrentHashMap(final Map<? extends K, ? extends V> m) {
        return new ConcurrentHashMap<>(m);
    }

    /**
     * Creates and returns a new instance of {@link ConcurrentLinkedQueue}.
     *

  interface StrongValueEntry<K, V, E extends InternalEntry<K, V, E>>
      extends InternalEntry<K, V, E> {}

  /** Marker interface for {@link InternalEntry} implementations for weak values. */
  interface WeakValueEntry<K, V, E extends InternalEntry<K, V, E>> extends InternalEntry<K, V, E> {
    /** Gets the weak value reference held by entry. */