code: public List<T> getSelectedValues() {
          Object[] curVal = (Object[]) $(listbox.getElement()).val();
  
          List<T> selectedValues = new ArrayList<>();
          if (curVal == null || curVal.length < 1) {
              return selectedValues;
          }
  
          List<String> keyIndex = getValuesKeyIndex();
          for (Object val : curVal) {
              if (val instanceof String) {
                  int selectedIndex = keyIndex.indexOf(val);
                  if (selectedIndex != -1) {
                      selectedValues.add(values.get(selectedIndex));
                  } else {
                      if (isTags() && val instanceof String) {
                          selectedValues.add((T) val);
                      }
                  }
              }
          }
          return selectedValues;
      }
docs: Get the selected vales from multiple combobox