* @since 2.0
 */
@GwtCompatible
public final class HashMultiset<E extends @Nullable Object> extends AbstractMapBasedMultiset<E> {

  /** Creates a new, empty {@code HashMultiset} using the default initial capacity. */
  public static <E extends @Nullable Object> HashMultiset<E> create() {
    return new HashMultiset<>();
  }

  /**
   * Creates a new, empty {@code HashMultiset} with the specified expected number of distinct
   * elements.

    Multiset<String> multiset = HashMultiset.create();
    Multiset<String> toRemove = HashMultiset.create(asList("a", "b", "a"));
    assertFalse(Multisets.removeOccurrences(multiset, toRemove));
    assertTrue(multiset.isEmpty());
  }

  public void testUnion() {
    Multiset<String> ms1 = HashMultiset.create(asList("a", "b", "a"));
    Multiset<String> ms2 = HashMultiset.create(asList("a", "b", "b", "c"));

    return new TestStringMultisetGenerator() {
      @Override
      protected Multiset<String> create(String[] elements) {
        return HashMultiset.create(asList(elements));
      }
    };
  }

  public void testCreate() {
    Multiset<String> multiset = HashMultiset.create();
    multiset.add("foo", 2);
    multiset.add("bar");
    assertEquals(3, multiset.size());
    assertEquals(2, multiset.count("foo"));
  }

    Multiset<String> c = HashMultiset.create();
    Multiset<String> multiset = ImmutableMultiset.copyOf(c);
    assertTrue(multiset.isEmpty());
  }

  public void testCopyOf_multiset_oneElement() {
    Multiset<String> c = HashMultiset.create(asList("a"));
    Multiset<String> multiset = ImmutableMultiset.copyOf(c);
    assertEquals(HashMultiset.create(asList("a")), multiset);
  }

    Multiset<String> c = HashMultiset.create();
    Multiset<String> multiset = ImmutableMultiset.copyOf(c);
    assertTrue(multiset.isEmpty());
  }

  public void testCopyOf_multiset_oneElement() {
    Multiset<String> c = HashMultiset.create(asList("a"));
    Multiset<String> multiset = ImmutableMultiset.copyOf(c);
    assertEquals(HashMultiset.create(asList("a")), multiset);
  }

    return new TestStringMultisetGenerator() {
      @Override
      protected Multiset<String> create(String[] elements) {
        return HashMultiset.create(asList(elements));
      }
    };
  }

  public void testCreate() {
    Multiset<String> multiset = HashMultiset.create();
    multiset.add("foo", 2);
    multiset.add("bar");
    assertEquals(3, multiset.size());
    assertEquals(2, multiset.count("foo"));
  }

    SerializableTester.reserializeAndAssert(multimap.asMap());
    Collection<Integer> valuesCopy = SerializableTester.reserialize(multimap.values());
    assertEquals(HashMultiset.create(multimap.values()), HashMultiset.create(valuesCopy));
  }

  @J2ktIncompatible
  @GwtIncompatible // SerializableTester
  public void testEmptySerialization() {

    SerializableTester.reserializeAndAssert(multimap.asMap());
    Collection<Integer> valuesCopy = SerializableTester.reserialize(multimap.values());
    assertEquals(HashMultiset.create(multimap.values()), HashMultiset.create(valuesCopy));
  }

  @J2ktIncompatible
  @GwtIncompatible // SerializableTester
  public void testEmptySerialization() {

    SerializableTester.reserializeAndAssert(multimap.asMap());
    Collection<Integer> valuesCopy = SerializableTester.reserialize(multimap.values());
    assertEquals(HashMultiset.create(multimap.values()), HashMultiset.create(valuesCopy));
  }

  @J2ktIncompatible
  @GwtIncompatible // SerializableTester
  public void testEmptySerialization() {

  }

  enum MultisetImpl implements CollectionsImplEnum {
    HashMultisetImpl {
      @Override
      public <E extends Comparable<E>> Multiset<E> create(Collection<E> contents) {
        return HashMultiset.create(contents);
      }
    },
    LinkedHashMultisetImpl {
      @Override
      public <E extends Comparable<E>> Multiset<E> create(Collection<E> contents) {