      /**
       * The constants used in this Content Widget.
       */
      public static interface CwConstants extends Constants,
          ContentWidget.CwConstants {
        String[] cwListBoxCars();

        String[] cwListBoxCategories();

        String cwListBoxDescription();

        String cwListBoxName();

        String cwListBoxSelectAll();

        String cwListBoxSelectCategory();

        String[] cwListBoxSports();

        String[] cwListBoxVacations();
      }

      /**
       * An instance of the constants.
       */
      private CwConstants constants;

      /**
       * Initialize this example.
       */
      @Override
      public Widget onInitialize() {
        // Create a panel to align the Widgets
        HorizontalPanel hPanel = new HorizontalPanel();
        hPanel.setSpacing(20);

        // Add a drop box with the list types
        final ListBox dropBox = new ListBox(false);
        String[] listTypes = constants.cwListBoxCategories();
        for (int i = 0; i < listTypes.length; i++) {
          dropBox.addItem(listTypes[i]);
        }
        dropBox.ensureDebugId("cwListBox-dropBox");
        VerticalPanel dropBoxPanel = new VerticalPanel();
        dropBoxPanel.setSpacing(4);
        dropBoxPanel.add(new HTML(constants.cwListBoxSelectCategory()));
        dropBoxPanel.add(dropBox);
        hPanel.add(dropBoxPanel);

        // Add a list box with multiple selection enabled
        final ListBox multiBox = new ListBox(true);
        multiBox.ensureDebugId("cwListBox-multiBox");
        multiBox.setWidth("11em");
        multiBox.setVisibleItemCount(10);
        VerticalPanel multiBoxPanel = new VerticalPanel();
        multiBoxPanel.setSpacing(4);
        multiBoxPanel.add(new HTML(constants.cwListBoxSelectAll()));
        multiBoxPanel.add(multiBox);
        hPanel.add(multiBoxPanel);

        // Add a handler to handle drop box events
        dropBox.addChangeHandler(new ChangeHandler() {
          public void onChange(ChangeEvent event) {
            showCategory(multiBox, dropBox.getSelectedIndex());
            multiBox.ensureDebugId("cwListBox-multiBox");
          }
        });

        // Show default category
        showCategory(multiBox, 0);
        multiBox.ensureDebugId("cwListBox-multiBox");

        // Return the panel
        return hPanel;
      }

      /**
       * Display the options for a given category in the list box.
       *
       * @param listBox the ListBox to add the options to
       * @param category the category index
       */
      private void showCategory(ListBox listBox, int category) {
        listBox.clear();
        String[] listData = null;
        switch (category) {
          case 0:
            listData = constants.cwListBoxCars();
            break;
          case 1:
            listData = constants.cwListBoxSports();
            break;
          case 2:
            listData = constants.cwListBoxVacations();
            break;
        }
        for (int i = 0; i < listData.length; i++) {
          listBox.addItem(listData[i]);
        }
      }