* writeObject} methods.
 *
 * @author Kevin Bourrillion
 */
@GwtCompatible
abstract class AbstractMapBasedMultiset<E extends @Nullable Object> extends AbstractMultiset<E>
    implements Serializable {

  transient ObjectCountHashMap<E> backingMap;
  transient long size;

  AbstractMapBasedMultiset(int distinctElements) {
    backingMap = newBackingMap(distinctElements);
  }

 *
 * @author Cliff L. Biffle
 * @author mike nonemacher
 * @since 2.0
 */
@J2ktIncompatible
@GwtIncompatible
public final class ConcurrentHashMultiset<E> extends AbstractMultiset<E> implements Serializable {

  /*
   * The ConcurrentHashMultiset's atomic operations are implemented primarily in terms of
   * AtomicInteger's atomic operations, with some help from ConcurrentMap's atomic operations on

 *
 * @author Cliff L. Biffle
 * @author mike nonemacher
 * @since 2.0
 */
@J2ktIncompatible
@GwtIncompatible
public final class ConcurrentHashMultiset<E> extends AbstractMultiset<E> implements Serializable {

  /*
   * The ConcurrentHashMultiset's atomic operations are implemented primarily in terms of
   * AtomicInteger's atomic operations, with some help from ConcurrentMap's atomic operations on

      builder.put(keyFunction.apply(value), value);
    }
    return builder.build();
  }

  static class Keys<K extends @Nullable Object, V extends @Nullable Object>
      extends AbstractMultiset<K> {
    @Weak final Multimap<K, V> multimap;

    Keys(Multimap<K, V> multimap) {
      this.multimap = multimap;
    }

    @Override
    Iterator<Multiset.Entry<K>> entryIterator() {

      builder.put(keyFunction.apply(value), value);
    }
    return builder.build();
  }

  static class Keys<K extends @Nullable Object, V extends @Nullable Object>
      extends AbstractMultiset<K> {
    @Weak final Multimap<K, V> multimap;

    Keys(Multimap<K, V> multimap) {
      this.multimap = multimap;
    }

    @Override
    Iterator<Multiset.Entry<K>> entryIterator() {

    successor(b, c);
  }

  /*
   * TODO(jlevy): Decide whether entrySet() should return entries with an equals() method that
   * calls the comparator to compare the two keys. If that change is made,
   * AbstractMultiset.equals() can simply check whether two multisets have equal entry sets.
   */

  /**
   * @serialData the comparator, the number of distinct elements, the first element, its count, the