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

        String cwNumberFormatFailedToParseInput();

        String cwNumberFormatFormattedLabel();

        String cwNumberFormatInvalidPattern();

        String cwNumberFormatName();

        String cwNumberFormatPatternLabel();

        String[] cwNumberFormatPatterns();

        String cwNumberFormatValueLabel();
      }

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

      /**
       * The {@link Label} where the formatted value is displayed.
       */
      private Label formattedBox = null;

      /**
       * The {@link TextBox} that displays the current pattern.
       */
      private TextBox patternBox = null;

      /**
       * The {@link ListBox} that holds the patterns.
       */
      private ListBox patternList = null;

      /**
       * The {@link TextBox} where the user enters a value.
       */
      private TextBox valueBox = null;

      /**
       * Initialize this example.
       */
      @Override
      public Widget onInitialize() {
        // Use a Grid to layout the content
        Grid layout = new Grid(4, 2);
        layout.setCellSpacing(5);

        // Add a field to select the pattern
        patternList = new ListBox();
        patternList.setWidth("17em");
        String[] patterns = constants.cwNumberFormatPatterns();
        for (String pattern : patterns) {
          patternList.addItem(pattern);
        }
        patternList.addChangeHandler(new ChangeHandler() {
          public void onChange(ChangeEvent event) {
            updatePattern();
          }
        });
        layout.setHTML(0, 0, constants.cwNumberFormatPatternLabel());
        layout.setWidget(0, 1, patternList);

        // Add a field to display the pattern
        patternBox = new TextBox();
        patternBox.setWidth("17em");
        patternBox.addKeyUpHandler(new KeyUpHandler() {
          public void onKeyUp(KeyUpEvent event) {
            updatePattern();
          }
        });
        layout.setWidget(1, 1, patternBox);

        // Add a field to set the value
        valueBox = new TextBox();
        valueBox.setWidth("17em");
        valueBox.setText("31415926535.897932");
        valueBox.addKeyUpHandler(new KeyUpHandler() {
          public void onKeyUp(KeyUpEvent event) {
            updateFormattedValue();
          }
        });
        layout.setHTML(2, 0, constants.cwNumberFormatValueLabel());
        layout.setWidget(2, 1, valueBox);

        // Add a field to display the formatted value
        formattedBox = new Label();
        formattedBox.setWidth("17em");
        layout.setHTML(3, 0, constants.cwNumberFormatFormattedLabel());
        layout.setWidget(3, 1, formattedBox);

        // Return the layout Widget
        updatePattern();
        return layout;
      }

      /**
       * Show an error message. Pass in null to clear the error message.
       *
       * @param errorMsg the error message
       */
      private void showErrorMessage(String errorMsg) {
        if (errorMsg == null) {
          formattedBox.removeStyleName("cw-RedText");
        } else {
          formattedBox.setText(errorMsg);
          formattedBox.addStyleName("cw-RedText");
        }
      }

      /**
       * Update the formatted value based on the user entered value and pattern.
       */
      private void updateFormattedValue() {
        String sValue = valueBox.getText();
        if (!sValue.equals("")) {
          try {
            double value = Double.parseDouble(sValue);
            String formattedValue = activeFormat.format(value);
            formattedBox.setText(formattedValue);
            showErrorMessage(null);
          } catch (NumberFormatException e) {
            showErrorMessage(constants.cwNumberFormatFailedToParseInput());
          }
        } else {
          formattedBox.setText("<None>");
        }
      }

      /**
       * Update the selected pattern based on the pattern in the list.
       */
      private void updatePattern() {
        switch (patternList.getSelectedIndex()) {
          case 0:
            activeFormat = NumberFormat.getDecimalFormat();
            patternBox.setText(activeFormat.getPattern());
            patternBox.setEnabled(false);
            break;
          case 1:
            activeFormat = NumberFormat.getCurrencyFormat();
            patternBox.setText(activeFormat.getPattern());
            patternBox.setEnabled(false);
            break;
          case 2:
            activeFormat = NumberFormat.getScientificFormat();
            patternBox.setText(activeFormat.getPattern());
            patternBox.setEnabled(false);
            break;
          case 3:
            activeFormat = NumberFormat.getPercentFormat();
            patternBox.setText(activeFormat.getPattern());
            patternBox.setEnabled(false);
            break;
          case 4:
            patternBox.setEnabled(true);
            String pattern = patternBox.getText();
            try {
              activeFormat = NumberFormat.getFormat(pattern);
            } catch (IllegalArgumentException e) {
              showErrorMessage(constants.cwNumberFormatInvalidPattern());
              return;
            }
            break;
        }

        // Update the formatted value
        updateFormattedValue();
      }