public static <E> Set<Set<E>> combinations(Set<E> set, final int size) {
    final ImmutableMap<E, Integer> index = Maps.indexMap(set);
    checkNonnegative(size, "size");
    checkArgument(size <= index.size(), "size (%s) must be <= set.size() (%s)", size, index.size());
    if (size == 0) {
      return ImmutableSet.<Set<E>>of(ImmutableSet.<E>of());
    } else if (size == index.size()) {
      return ImmutableSet.<Set<E>>of(index.keySet());

     */
    @Override
    public ImmutableBiMap<K, V> buildOrThrow() {
      if (size == 0) {
        return of();
      }
      if (valueComparator != null) {
        if (entriesUsed) {
          alternatingKeysAndValues = Arrays.copyOf(alternatingKeysAndValues, 2 * size);
        }
        sortEntries(alternatingKeysAndValues, size, valueComparator);
      }
      entriesUsed = true;

     * added.
     *
     * @throws IllegalArgumentException if duplicate key pairs were added
     * @since 31.0
     */
    public ImmutableTable<R, C, V> buildOrThrow() {
      int size = cells.size();
      switch (size) {
        case 0:
          return of();
        case 1:
          return new SingletonImmutableTable<>(Iterables.getOnlyElement(cells));
        default:

    if (generate != null) {
      ImmutableList<Parameter> params = Invokable.from(generate).getParameters();
      List<Object> args = Lists.newArrayListWithCapacity(params.size());
      TypeVariable<?>[] typeVars = rawType.getTypeParameters();
      for (int i = 0; i < params.size(); i++) {
        TypeToken<?> paramType = type.resolveType(typeVars[i]);
        // We require all @Generates methods to either be parameter-less or accept non-null

      boolean timed,
      long timeout,
      TimeUnit unit)
      throws InterruptedException, ExecutionException, TimeoutException {
    checkNotNull(executorService);
    checkNotNull(unit);
    int ntasks = tasks.size();
    checkArgument(ntasks > 0);
    List<Future<T>> futures = Lists.newArrayListWithCapacity(ntasks);
    BlockingQueue<Future<T>> futureQueue = Queues.newLinkedBlockingQueue();
    long timeoutNanos = unit.toNanos(timeout);

    }
  }

  public void testSize0() {
    Iterator<String> iterator = Iterators.emptyIterator();
    assertEquals(0, Iterators.size(iterator));
  }

  public void testSize1() {
    Iterator<Integer> iterator = Collections.singleton(0).iterator();
    assertEquals(1, Iterators.size(iterator));
  }

  public void testSize_partiallyConsumed() {
    Iterator<Integer> iterator = asList(1, 2, 3, 4, 5).iterator();

  static final int MAX_TABLE_SIZE = Ints.MAX_POWER_OF_TWO;

  // Represents how tightly we can pack things, as a maximum.
  private static final double DESIRED_LOAD_FACTOR = 0.7;

  // If the set has this many elements, it will "max out" the table size
  private static final int CUTOFF = (int) (MAX_TABLE_SIZE * DESIRED_LOAD_FACTOR);

  /**

   *     partitions
   * @throws IllegalArgumentException if {@code size} is nonpositive
   */
  public static <T extends @Nullable Object> UnmodifiableIterator<List<T>> partition(
      Iterator<T> iterator, int size) {
    return partitionImpl(iterator, size, false);
  }

  /**
   * Divides an iterator into unmodifiable sublists of the given size, padding the final iterator

      int size = 0;
      for (int i = 0; i < length; i++) {
        if (counts[i] > 0) {
          elements[size] = elements[i];
          counts[size] = counts[i];
          size++;
        }
      }
      Arrays.fill(elements, size, length, null);
      Arrays.fill(counts, size, length, 0);
      length = size;
    }

    /**