code: public void addOrder(String columnName, boolean ascending) {
      if (columnName == null) {
        return;
      }
      for (int i = 0; i < columns.size(); i++) {
        if (!columnName.equals(columns.get(i).getData())) {
          continue;
        }
        order.add(new Order(i, ascending ? "asc" : "desc"));
      }
    }
docs: Add an order on the given column
  
  @param columnName the name of the column
  @param ascending whether the sorting is ascending or descending