public ControlPanel() {
   winSel.setCaption("Controlled window:");
   winSel.setContainerDataSource(windowlist);
   winSel.setValue(windowlist.firstItemId());
   winSel.setItemCaptionPropertyId("caption");
   addComponent(winSel);
   addComponent(bf);
   addComponent(toggleModality);
   bf.addClickListener(this);
   toggleModality.addClickListener(this);
 }
  @Override
  protected void init(VaadinRequest request) {
    ComboBox themePicker = new ComboBox("Theme", Arrays.asList(themes));
    themePicker.setValue(getTheme());

    themePicker.addValueChangeListener(
        new ValueChangeListener() {
          @Override
          public void valueChange(ValueChangeEvent event) {
            String theme = (String) event.getProperty().getValue();
            setTheme(theme);
          }
        });

    setContent(themePicker);
  }