code: @Override
      public String getValue() {
          switch (getSelectedIndex()) {
          case 0:
              if (internVal == null) return null;
              internVal = getValue1();
              return internVal;
          case 1:
              internVal = getValue2();
              return internVal;
          default:
              return null;
          }
      }
docs: Returns the currently selected value or null if there is no currently
  selected button