code: private void shift(final String _key)
      {
          for (int i = this.threshold; i > 0; i--) {
              this.props.setProperty(_key + i, this.props.getProperty(_key + (i - 1), "").trim());
          }
          int i = this.threshold + 1;
          while (this.props.contains(_key + i)) {
              this.props.remove(_key + i);
              i++;
          }
      }
docs: Shift a property.
  
  @param _key key the property must be shifted for