* @throws NullPointerException if any key or value in {@code map} is null
   */
  public static <K, V> ImmutableBiMap<K, V> copyOf(Map<? extends K, ? extends V> map) {
    if (map instanceof ImmutableBiMap) {
      @SuppressWarnings("unchecked") // safe since map is not writable
      ImmutableBiMap<K, V> bimap = (ImmutableBiMap<K, V>) map;
      // TODO(lowasser): if we need to make a copy of a BiMap because the

   * @throws NullPointerException if any key or value in {@code map} is null
   */
  public static <K, V> ImmutableBiMap<K, V> copyOf(Map<? extends K, ? extends V> map) {
    if (map instanceof ImmutableBiMap) {
      @SuppressWarnings("unchecked") // safe since map is not writable
      ImmutableBiMap<K, V> bimap = (ImmutableBiMap<K, V>) map;
      // TODO(lowasser): if we need to make a copy of a BiMap because the

  }

  public void testOf() {
    assertMapEquals(ImmutableBiMap.of("one", 1), "one", 1);
    assertMapEquals(ImmutableBiMap.of("one", 1).inverse(), 1, "one");
    assertMapEquals(ImmutableBiMap.of("one", 1, "two", 2), "one", 1, "two", 2);
    assertMapEquals(ImmutableBiMap.of("one", 1, "two", 2).inverse(), 1, "one", 2, "two");
    assertMapEquals(
        ImmutableBiMap.of("one", 1, "two", 2, "three", 3), "one", 1, "two", 2, "three", 3);

  @LazyInit @RetainedWith @CheckForNull private transient ImmutableBiMap<V, K> inverse;

  @Override
  public ImmutableBiMap<V, K> inverse() {
    if (isEmpty()) {
      return ImmutableBiMap.of();
    }
    ImmutableBiMap<V, K> result = inverse;
    return (result == null) ? inverse = new Inverse() : result;
  }

  private final class Inverse extends ImmutableBiMap<V, K> {

    @Override
    public int size() {

  }

  @CheckForNull private final transient ImmutableBiMap<V, K> inverse;
  @LazyInit @RetainedWith @CheckForNull private transient ImmutableBiMap<V, K> lazyInverse;

  @Override
  public ImmutableBiMap<V, K> inverse() {
    if (inverse != null) {
      return inverse;
    } else {
      // racy single-check idiom
      ImmutableBiMap<V, K> result = lazyInverse;
      if (result == null) {

  public static class ImmutableBiMapGenerator extends TestStringBiMapGenerator {
    @Override
    protected BiMap<String, String> create(Entry<String, String>[] entries) {
      ImmutableBiMap.Builder<String, String> builder = ImmutableBiMap.builder();
      for (Entry<String, String> entry : entries) {
        checkNotNull(entry);
        builder.put(entry.getKey(), entry.getValue());
      }
      return builder.build();
    }

          }
        }
        return ImmutableBiMap.copyOf(sourceMap);
      }
    },
    COPY_OF_ENTRIES {
      @Override
      public ImmutableBiMap<Object, Object> create(List<Entry<?, ?>> entries) {
        return ImmutableBiMap.copyOf(entries);
      }
    },
    BUILDER_PUT_ONE_BY_ONE {
      @Override
      public ImmutableBiMap<Object, Object> create(List<Entry<?, ?>> entries) {

  public static class ImmutableBiMapGenerator extends TestStringBiMapGenerator {
    @Override
    protected BiMap<String, String> create(Entry<String, String>[] entries) {
      ImmutableBiMap.Builder<String, String> builder = ImmutableBiMap.builder();
      for (Entry<String, String> entry : entries) {
        checkNotNull(entry);
        builder.put(entry.getKey(), entry.getValue());
      }
      return builder.build();
    }

          .put(SortedMultiset.class, ImmutableSortedMultiset.of())
          .put(ImmutableSortedMultiset.class, ImmutableSortedMultiset.of())
          .put(BiMap.class, ImmutableBiMap.of())
          .put(ImmutableBiMap.class, ImmutableBiMap.of())
          .put(Table.class, ImmutableTable.of())
          .put(ImmutableTable.class, ImmutableTable.of())

  }

  static <T extends @Nullable Object, K, V> Collector<T, ?, ImmutableBiMap<K, V>> toImmutableBiMap(
      Function<? super T, ? extends K> keyFunction,
      Function<? super T, ? extends V> valueFunction) {
    checkNotNull(keyFunction);
    checkNotNull(valueFunction);
    return Collector.of(
        ImmutableBiMap.Builder<K, V>::new,