code: private void updateColumnMetaData(CfDef columnFamily, ByteBuffer columnName, String validationClass)
      {
          ColumnDef column = getColumnDefByName(columnFamily, columnName);
  
          if (column != null)
          {
              // if validation class is the same - no need to modify it
              if (column.getValidation_class().equals(validationClass))
                  return;
  
              // updating column definition with new validation_class
              column.setValidation_class(validationClass);
          }
          else
          {
              List<ColumnDef> columnMetaData = new ArrayList<ColumnDef>(columnFamily.getColumn_metadata());
              columnMetaData.add(new ColumnDef(columnName, validationClass));
              columnFamily.setColumn_metadata(columnMetaData);
          }
      }
docs: Used to locally update column family definition with new column metadata
  @param columnFamily    - CfDef record
  @param columnName      - column name represented as byte[]
  @param validationClass - value validation class