code: void addValue(int columnIndex, String value)
      {
          if ( (columnIndex < 0) || (columnIndex >= data.size()) )
          {
              throw new IllegalArgumentException();
          }
  
          List<String> stringList = data.get(columnIndex);
          stringList.add(value);
      }
docs: Add a value to the nth column
  
  @param columnIndex n
  @param value       value to add