public List getValues(int row, int column);

    /**
     * Returns a list (possibly empty) of the values for the specified item.
     * The returned list should be unmodifiable.
     * 
     * @param rowKey  the row key (<code>null</code> not permitted).
     * @param columnKey  the column key (<code>null</code> not permitted).
     *
     * @return The list of values.
     */
    public List getValues(Comparable rowKey, Comparable columnKey);