ToOptionalState::new,
          (state, o) -> state.add((o == null) ? NULL_PLACEHOLDER : o),
          ToOptionalState::combine,
          state -> {
            Object result = state.getElement();
            return (result == NULL_PLACEHOLDER) ? null : result;
          },
          Collector.Characteristics.UNORDERED);

  /**

     */
    public Indexed(final T element, final int index) {
        this.element = element;
        this.index = index;
    }

    /**
     * 要素を返します。
     *
     * @return 要素
     */
    public T getElement() {
        return element;
    }

    /**
     * インデックスを返します。
     *
     * @return インデックス
     */
    public int getIndex() {
        return index;
    }

      elements = new Object[distinct];
      counts = new int[distinct];
      int i = 0;
      for (Entry<? extends Object> entry : multiset.entrySet()) {
        elements[i] = entry.getElement();
        counts[i] = entry.getCount();
        i++;
      }
    }

    Object readResolve() {
      ImmutableMultiset.Builder<Object> builder =

     * represent the same element and count. That is, two entries {@code a} and {@code b} are equal
     * if:
     *
     * <pre>{@code
     * Objects.equal(a.getElement(), b.getElement())
     *     && a.getCount() == b.getCount()
     * }</pre>
     */
    @Override
    // TODO(kevinb): check this wrt TreeMultiset?
    boolean equals(@CheckForNull Object o);

    /**

          @Override
          @ParametricNullness
          public E getElement() {
            return mapEntry.getKey();
          }

          @Override
          public int getCount() {
            Count count = mapEntry.getValue();
            if (count == null || count.get() == 0) {
              Count frequency = backingMap.get(getElement());
              if (frequency != null) {

    long size = 0;
    for (int i = 0; i < entriesArray.length; i++) {
      Entry<E> entry = entriesArray[i];
      int count = entry.getCount();
      size += count;
      E element = checkNotNull(entry.getElement());
      delegateMap.put(element, count);
      if (!(entry instanceof Multisets.ImmutableEntry)) {
        entriesArray[i] = Multisets.immutableEntry(element, count);
      }
    }

     * represent the same element and count. That is, two entries {@code a} and {@code b} are equal
     * if:
     *
     * <pre>{@code
     * Objects.equal(a.getElement(), b.getElement())
     *     && a.getCount() == b.getCount()
     * }</pre>
     */
    @Override
    // TODO(kevinb): check this wrt TreeMultiset?
    boolean equals(@CheckForNull Object o);

    /**

   * either of these would recurse back to us again!
   */
  private List<E> snapshot() {
    List<E> list = newArrayListWithExpectedSize(size());
    for (Multiset.Entry<E> entry : entrySet()) {
      E element = entry.getElement();
      for (int i = entry.getCount(); i > 0; i--) {
        list.add(element);
      }
    }
    return list;
  }

  // Modification Operations

  /**

    int entryCount = multiset.entrySet().size();
    stream.writeInt(entryCount);
    for (Multiset.Entry<E> entry : multiset.entrySet()) {
      stream.writeObject(entry.getElement());
      stream.writeInt(entry.getCount());
    }
  }

  /**
   * Populates a multiset by reading an input stream, as part of deserialization. See {@link
   * #writeMultiset} for the data format.
   */

    int entryCount = multiset.entrySet().size();
    stream.writeInt(entryCount);
    for (Multiset.Entry<E> entry : multiset.entrySet()) {
      stream.writeObject(entry.getElement());
      stream.writeInt(entry.getCount());
    }
  }

  /**
   * Populates a multiset by reading an input stream, as part of deserialization. See {@link
   * #writeMultiset} for the data format.
   */