abstract ObjectCountHashMap<E> newBackingMap(int distinctElements);

  @Override
  public final int count(@CheckForNull Object element) {
    return backingMap.get(element);
  }

  // Optional Operations - Modification Operations

  /**
   * {@inheritDoc}
   *
   * @throws IllegalArgumentException if the call would result in more than {@link
   *     Integer#MAX_VALUE} occurrences of {@code element} in this multiset.
   */

 * IteratorTester#newTargetIterator()} method. This is because it's impossible to test an Iterator
 * without changing its state, so the tester needs a steady supply of fresh Iterators.
 *
 * <p>If your iterator supports modification through {@code remove()}, you may wish to override the
 * verify() method, which is called after each sequence and is guaranteed to be called

      derivedFeatures.add(CollectionFeature.REJECTS_DUPLICATES_AT_CREATION);
    }
    if (mapFeatures.contains(MapFeature.FAILS_FAST_ON_CONCURRENT_MODIFICATION)) {
      derivedFeatures.add(CollectionFeature.FAILS_FAST_ON_CONCURRENT_MODIFICATION);
    }
    // add the intersection of CollectionFeature.values() and mapFeatures
    for (CollectionFeature feature : CollectionFeature.values()) {

    suite.addTest(
        MultisetTestSuiteBuilder.using(hashMultisetGenerator())
            .withFeatures(
                CollectionSize.ANY,
                CollectionFeature.FAILS_FAST_ON_CONCURRENT_MODIFICATION,
                CollectionFeature.ALLOWS_NULL_VALUES,
                CollectionFeature.SERIALIZABLE,
                CollectionFeature.GENERAL_PURPOSE,
                MultisetFeature.ENTRIES_ARE_VIEWS)

  ALLOWS_ANY_NULL_QUERIES(
      ALLOWS_NULL_ENTRY_QUERIES, ALLOWS_NULL_KEY_QUERIES, ALLOWS_NULL_VALUE_QUERIES),
  RESTRICTS_KEYS,
  RESTRICTS_VALUES,
  SUPPORTS_PUT,
  SUPPORTS_REMOVE,
  FAILS_FAST_ON_CONCURRENT_MODIFICATION,
  /**
   * Indicates that the constructor or factory method of a map, usually an immutable map, throws an
   * {@link IllegalArgumentException} when presented with duplicate keys instead of discarding all
   * but one.

                MapFeature.ALLOWS_NULL_VALUES,
                MapFeature.ALLOWS_ANY_NULL_QUERIES,
                MapFeature.GENERAL_PURPOSE,
                MapFeature.FAILS_FAST_ON_CONCURRENT_MODIFICATION,
                CollectionFeature.SUPPORTS_ITERATOR_REMOVE,
                CollectionFeature.SERIALIZABLE,
                CollectionSize.ANY)
            .createTestSuite());

   * allocated, the value of {@code metadata} combines the number of bits in the "short hash", in
   * its bottom {@value CompactHashing#HASH_TABLE_BITS_MAX_BITS} bits, with a modification count in
   * the remaining bits that is used to detect concurrent modification during iteration.
   */
  private transient int metadata;

  /** The number of elements contained in the set. */
  private transient int size;

  /**
   * Returns a copy of the input string in which all {@linkplain #isUpperCase(char) uppercase ASCII
   * characters} have been converted to lowercase. All other characters are copied without
   * modification.
   */
  public static String toLowerCase(String string) {
    int length = string.length();
    for (int i = 0; i < length; i++) {
      if (isUpperCase(string.charAt(i))) {

  private int hashTableMask() {
    return (1 << (metadata & CompactHashing.HASH_TABLE_BITS_MASK)) - 1;
  }

  void incrementModCount() {
    metadata += CompactHashing.MODIFICATION_COUNT_INCREMENT;
  }

  @CanIgnoreReturnValue
  @Override
  public boolean add(@ParametricNullness E object) {
    if (needsAllocArrays()) {
      allocArrays();
    }

   * AtomicInteger's atomic operations, with some help from ConcurrentMap's atomic operations on
   * creation and removal (including automatic removal of zeroes). If the modification of an
   * AtomicInteger results in zero, we compareAndSet the value to zero; if that succeeds, we remove
   * the entry from the Map. If another operation sees a zero in the map, it knows that the entry is