}

  /**
   * {@inheritDoc}
   *
   * @throws NullPointerException if {@code columnKey} is {@code null}
   */
  @Override
  public ImmutableMap<R, V> column(C columnKey) {
    checkNotNull(columnKey, "columnKey");
    return MoreObjects.firstNonNull(
        (ImmutableMap<R, V>) columnMap().get(columnKey), ImmutableMap.<R, V>of());
  }

  @Override
  public ImmutableSet<C> columnKeySet() {

        @ParametricNullness C columnKey,
        @ParametricNullness V value) {
      this.rowKey = rowKey;
      this.columnKey = columnKey;
      this.value = value;
    }

    @Override
    @ParametricNullness
    public R getRowKey() {
      return rowKey;
    }

    @Override
    @ParametricNullness
    public C getColumnKey() {
      return columnKey;
    }

    @Override

    return containsRow(rowKey) && containsColumn(columnKey);
  }

  /**
   * Returns {@code true} if the provided column key is among the column keys provided when the
   * table was constructed.
   */
  @Override
  public boolean containsColumn(@CheckForNull Object columnKey) {
    return columnKeyToIndex.containsKey(columnKey);
  }

  /**

      R rowKey = cell.getRowKey();
      C columnKey = cell.getColumnKey();
      // The requireNonNull calls are safe because we construct the indexes with indexMap.
      int rowIndex = requireNonNull(rowKeyToIndex.get(rowKey));
      int columnIndex = requireNonNull(columnKeyToIndex.get(columnKey));
      V existingValue = values[rowIndex][columnIndex];
      checkNoDuplicate(rowKey, columnKey, existingValue, cell.getValue());

      R rowKey = cell.getRowKey();
      C columnKey = cell.getColumnKey();
      // The requireNonNull calls are safe because we construct the indexes with indexMap.
      int rowIndex = requireNonNull(rowKeyToIndex.get(rowKey));
      int columnIndex = requireNonNull(columnKeyToIndex.get(columnKey));
      V existingValue = values[rowIndex][columnIndex];
      checkNoDuplicate(rowKey, columnKey, existingValue, cell.getValue());

      return (Table<R, C, V>) super.delegate();
    }

    @Override
    public boolean contains(@CheckForNull Object rowKey, @CheckForNull Object columnKey) {
      synchronized (mutex) {
        return delegate().contains(rowKey, columnKey);
      }
    }

    @Override
    public boolean containsRow(@CheckForNull Object rowKey) {
      synchronized (mutex) {

      return (Table<R, C, V>) super.delegate();
    }

    @Override
    public boolean contains(@CheckForNull Object rowKey, @CheckForNull Object columnKey) {
      synchronized (mutex) {
        return delegate().contains(rowKey, columnKey);
      }
    }

    @Override
    public boolean containsRow(@CheckForNull Object rowKey) {
      synchronized (mutex) {

   * referencing the type variables seem worthwhile.
   */
  final void checkNoDuplicate(R rowKey, C columnKey, @CheckForNull V existingValue, V newValue) {
    checkArgument(
        existingValue == null,
        "Duplicate key: (row=%s, column=%s), values: [%s, %s].",
        rowKey,
        columnKey,
        newValue,
        existingValue);
  }

  // redeclare to satisfy our test for b/310253115

 *
 * <p>Lookups by row key are often faster than lookups by column key, because the data is stored in
 * a {@code Map<R, Map<C, V>>}. A method call like {@code column(columnKey).get(rowKey)} still runs
 * quickly, since the row key is provided. However, {@code column(columnKey).size()} takes longer,
 * since an iteration across all row keys occurs.
 *
 * <p>Because a {@code TreeBasedTable} has unique sorted values for a given row, both {@code

                    List<Integer> columnKeys = Lists.newArrayList();
                    for (Object element : elements) {
                      @SuppressWarnings("unchecked")
                      Cell<String, Integer, Character> cell =
                          (Cell<String, Integer, Character>) element;
                      columnKeys.add(cell.getColumnKey());
                    }