@Override
  int hashCode();

  /**
   * {@inheritDoc}
   *
   * <p>It is recommended, though not mandatory, that this method return the result of invoking
   * {@link #toString} on the {@link #entrySet}, yielding a result such as {@code [a x 3, c, d x 2,
   * e]}.
   */
  @Override
  String toString();

  // Refined Collection Methods

  /**
   * {@inheritDoc}
   *