code: public void setSelectedIndex (int selidx)
      {
          // update the display
          updateSelection(selidx);
  
          // let the model know what's up
          Object item = (selidx == -1) ? null : _model.getElementAt(selidx);
          _model.setSelectedItem(item);
      }
docs: Sets the index of the selected component. A value of -1 will clear
  the selection.