sclass ShowComboBoxForm {
  S desc;
  S itemDesc;
  LS items;
  S defaultValue;
  IVF1<S> action;
  JComboBox cb;
  
  S selected() { ret selectedItem(cb); }
  
  void run aka show() {
    cb = jComboBox(items, defaultValue);
    showFormTitled(desc, 
      "", jlabel(desc),
      itemDesc, cb,
      rThread {
        S item = selected();
        printVars(+item, +action);
        if (nempty(item))
          action.get(item);
      });
  }
}