code: public int getMappedColumn(final int renderCol) {
          if (columnMapping == null || renderCol == -1) {
              return renderCol;
          }
          else {
              final Integer result = columnMapping.get(renderCol);
              if (result == null) {
                  throw new IllegalArgumentException("Invalid index " + renderCol);
              }
              return result;
          }
      }
docs: Maps the rendered column index to the real column index.
  
  @param renderCol the rendered index
  @return the mapped index