Preventing ToggleButton from being unselected when in ToggleGroup

Question

As explained here http://docs.oracle.com/javafx/2/ui_controls/toggle-button.htm and shown in the code below, unlike RadioButton, ToggleButton can be deselected even when they are in a ToggleGroup.
public class Main extends Application {
     * @param args the command line arguments
    public static void main(String[] args) {
        launch(args);
    @Override
    public void start(Stage primaryStage) {
        GridPane grid = GridPaneBuilder.create().build();
        for (int rowIndex = 0; rowIndex < 2; rowIndex++) {
            ToggleGroup group = ToggleGroupBuilder.create().build();
            for (int columnIndex = 0; columnIndex < 5; columnIndex++) {
                Node node = null;
                switch (rowIndex) {
                    case 0: {
                        node = ToggleButtonBuilder.create().toggleGroup(group).text(String.valueOf(columnIndex)).build();
                    break;
                    case 1: {
                        node = RadioButtonBuilder.create().toggleGroup(group).text(String.valueOf(columnIndex)).build();
                GridPane.setConstraints(node, columnIndex, rowIndex);
                GridPane.setHgrow(node, Priority.ALWAYS);
                grid.getChildren().add(node);
        Scene scene = new Scene(grid);
        primaryStage.setTitle("Test_ToggleGroup");
        primaryStage.setScene(scene);
        primaryStage.show();
}This is a behavior I'd like to change as I never want to achieve a state where there is no ToggleButton selected in the group.
I've already try setting up some listeners on the button or it's skin to intercept mouse clicks call but consuming the even seemed to be ignored (probably the listener is not set on the proper object).
I am thinking of putting a listener on the selectedToggle property of the ToggleGroup but to force the button to remain selected but this seems artificial and prone to break.
Another idea would be to decorate RadioButton to appear like a ToggleButton but I have problem getting rid of the radio region of the RadioButton skin. Whenever I try to make it non-visible, the empty space it takes is still showing on screen, I've tried redefining its shape as well to no avail.
Any clue?

Answer 1

Hi. Please try the following:
import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.*;
import javafx.scene.control.*;
import javafx.scene.layout.*;
import javafx.stage.Stage;
import javafx.beans.value.*;
public class TogglB extends Application {
    public static void main(String[] args) {
        launch(args);
    @Override
    public void start(Stage primaryStage) {
        primaryStage.setTitle("Hello World!");
        final ToggleGroup group = new ToggleGroup();
        ToggleButton tb1 = new ToggleButton("Minor");
        tb1.setToggleGroup(group);
        tb1.setSelected(true);
        ToggleButton tb2 = new ToggleButton("Major");
        tb2.setToggleGroup(group);
        ToggleButton tb3 = new ToggleButton("Critical");
        tb3.setToggleGroup(group);
        HBox root = new HBox();
        group.selectedToggleProperty().addListener(new ChangeListener<Toggle>() {
            public void changed(ObservableValue<? extends Toggle> ov,
                    Toggle toggle, Toggle new_toggle) {
                if (new_toggle == null) {
                    toggle.setSelected(true);
        root.getChildren().addAll(tb1, tb2, tb3);
        primaryStage.setScene(new Scene(root, 300, 250));
        primaryStage.show();
}