code: public void show() {
          setListSelection(comboBox.getSelectedIndex());
  
          Point location = getPopupLocation();
  
          show(comboBox, location.x, location.y);
  
          // For some reason, this is needed to clear the old selection being
          // displayed. Calling list.clearSelection() doesn't cut it.
          list.repaint();
      }
docs: Implementation of ComboPopup.show().