*
 * <p>The allowed row and column keys must be supplied when the table is created. The table always
 * contains a mapping for every row key / column pair. The value corresponding to a given row and
 * column is null unless another value is provided.
 *
 * <p>The table's size is constant: the product of the number of supplied row keys and the number of

 * Table} interface.
 *
 * <p>The views returned by {@link #column}, {@link #columnKeySet()}, and {@link #columnMap()} have
 * iterators that don't support {@code remove()}. Otherwise, all optional operations are supported.
 * Null row keys, columns keys, and values are not supported.
 *
 * <p>Lookups by row key are often faster than lookups by column key, because the data is stored in

 * Table} interface.
 *
 * <p>The views returned by {@link #column}, {@link #columnKeySet()}, and {@link #columnMap()} have
 * iterators that don't support {@code remove()}. Otherwise, all optional operations are supported.
 * Null row keys, columns keys, and values are not supported.
 *
 * <p>Lookups by row key are often faster than lookups by column key, because the data is stored in

   *
   * <p>The views returned by the {@code Table} methods {@link Table#column}, {@link
   * Table#columnKeySet}, and {@link Table#columnMap} have iterators that don't support {@code
   * remove()}. Otherwise, all optional operations are supported. Null row keys, columns keys, and
   * values are not supported.
   *
   * <p>Lookups by row key are often faster than lookups by column key, because the data is stored

      table.put(row, 2, 'b');
    }
  }

  private static void populateForColumnKeySet(
      Table<Integer, String, Character> table, String[] elements) {
    for (String column : elements) {
      table.put(1, column, 'a');
      table.put(2, column, 'b');
    }
  }

  private static void populateForValues(
      Table<Integer, Character, String> table, String[] elements) {
    for (int i = 0; i < elements.length; i++) {

   * @return the corresponding map from column keys to values
   */
  Map<C, V> row(@ParametricNullness R rowKey);

  /**
   * Returns a view of all mappings that have the given column key. For each row key / column key /
   * value mapping in the table with that column key, the returned map associates the row key with
   * the value. If no mappings in the table have the provided column key, an empty map is returned.
   *

   *
   * <p>The returned map's views have iterators that don't support {@code remove()}.
   */
  @Override
  public Map<R, V> column(C columnKey) {
    return new Column(columnKey);
  }

  private final class Column extends ViewCachingAbstractMap<R, V> {
    final C columnKey;

    Column(C columnKey) {
      this.columnKey = checkNotNull(columnKey);
    }

    @Override

 * order of the various views.
 *
 * <p>The views returned by {@link #column}, {@link #columnKeySet()}, and {@link #columnMap()} have
 * iterators that don't support {@code remove()}. Otherwise, all optional operations are supported.
 * Null row keys, columns keys, and values are not supported.
 *
 * <p>Lookups by row key are often faster than lookups by column key, because the data is stored in

 * order of the various views.
 *
 * <p>The views returned by {@link #column}, {@link #columnKeySet()}, and {@link #columnMap()} have
 * iterators that don't support {@code remove()}. Otherwise, all optional operations are supported.
 * Null row keys, columns keys, and values are not supported.
 *
 * <p>Lookups by row key are often faster than lookups by column key, because the data is stored in

    assertEquals(ImmutableMap.of("foo", 'a', "bar", 'b'), table.column(1));
  }

  // This test assumes that the implementation does not support null keys.
  public void testColumnNull() {
    table = create("foo", 1, 'a', "bar", 1, 'b', "foo", 3, 'c');
    assertThrows(NullPointerException.class, () -> table.column(null));
  }

  public void testColumnSetPartialOverlap() {