code: public final String getColumnName(int index) {
      if (index < 0 || index >= columns.size()) {
        throw new InvalidOperationException("Invalid column index: " + index);
      }
      return columns.get(index);
    }
docs: Get column name.
  @param index Column index between <code>0</code> and <code>getColumnCount() - 1</code>
  @return Name of column.