/**
   * A collector that converts a stream of zero or one elements to an {@code Optional}.
   *
   * @throws IllegalArgumentException if the stream consists of two or more elements.
   * @throws NullPointerException if any element in the stream is {@code null}.
   * @return {@code Optional.of(onlyElement)} if the stream has exactly one element (must not be
   *     {@code null}) and returns {@code Optional.empty()} if it has none.

    suite.addTest(
        SetTestSuiteBuilder.using(
                new TestStringSetGenerator() {
                  @Override
                  protected Set<String> create(String[] elements) {
                    return CompactHashSet.create(asList(elements));
                  }
                })
            .named("CompactHashSet")
            .withFeatures(allFeatures)
            .createTestSuite());
    suite.addTest(

    Iterator<E> iterator = collection.iterator();
    Object element = iterator.next();
    // If it's an Entry, it may become invalid once it's removed from the Map. Copy it.
    if (element instanceof Entry) {
      Entry<?, ?> entry = (Entry<?, ?>) element;
      element = mapEntry(entry.getKey(), entry.getValue());
    }
    assertTrue(collection.contains(element)); // sanity check
    iterator.remove();

      }

      @Override
      public T set(int index, T element) {
        return data.set(index, element);
      }

      @Override
      public boolean add(T element) {
        return data.add(element);
      }

      @Override
      public void add(int index, T element) {
        data.add(index, element);
      }

      @Override
      public T remove(int index) {

     * any of the algorithm name is not supported. The returned collection has equal count of elements as passed in
     * collection of names, and if names contains duplicated elements, the returned list of algorithms will have
     * duplicates as well.
     *
     * @throws ChecksumAlgorithmServiceException if any asked algorithm name is not supported.

   * objects per entry.  Instead we use an open-addressed hash table.  This design is basically
   * equivalent to RegularImmutableSet, save that instead of having a hash table containing the
   * elements directly and null for empty positions, we store indices of the keys in the hash table,
   * and ABSENT for empty positions.  We then look up the keys in alternatingKeysAndValues.
   *

  public SampleElements<Entry<K, V>> samples() {
    return SampleElements.mapEntries(keys, values);
  }

  @Override
  public Set<Entry<K, V>> create(Object... elements) {
    Entry<K, V>[] entries = createArray(elements.length);
    arraycopy(elements, 0, entries, 0, elements.length);
    return createFromEntries(entries);
  }

  public abstract Set<Entry<K, V>> createFromEntries(Entry<K, V>[] entries);

  @Override

  @CollectionFeature.Require(ALLOWS_NULL_VALUES)
  public void testEquals_containingNull() {
    ArrayList<E> elements = new ArrayList<>(getSampleElements());
    elements.set(elements.size() / 2, null);
    collection = getSubjectGenerator().create(elements.toArray());
    List<E> other = new ArrayList<>(getSampleElements());
    assertFalse(

        return elements;
    }

    /**
     * {@literal byte}の配列を返します。
     *
     * @param elements
     *            配列の要素
     * @return 配列
     */
    public static byte[] asByteArray(final byte... elements) {
        return elements;
    }

    /**
     * {@literal short}の配列を返します。
     *
     * @param elements
     *            配列の要素
     * @return 配列
     */

  private SortedIterables() {}

  /**
   * Returns {@code true} if {@code elements} is a sorted collection using an ordering equivalent to
   * {@code comparator}.
   */
  public static boolean hasSameComparator(Comparator<?> comparator, Iterable<?> elements) {
    checkNotNull(comparator);
    checkNotNull(elements);
    Comparator<?> comparator2;
    if (elements instanceof SortedSet) {
      comparator2 = comparator((SortedSet<?>) elements);