Swing: Intercept click on a JRadiobutton

Question

I want to intercept the click on a JRadioButton in a button group. More precise: When JRadioButton A is chosen and the user clicks on JRadioButton B, I want to show a Yes/No-option pane. Only when the user clicks "Yes", radio button B be will be selected. If the user clicks on "No" nothing is supposed to change. Is this or rather how is this possible?

Answer 1

You want to listen for ItemEvents to know when the first button is selected (see this). You can use AbstractButton#isSelected to check that the other button is selected. Finally, you can use JOptionPane#showConfirmDialog(Component, Object, String, int) to prompt the user for "Yes" or "No," and use something like AbstractButton#setSelected(boolean) or ButtonGroup#clearSelection to control which buttons are selected.

This should get you started down the right track.

Answer 2

Add an ItemListener to the B radio button. Refer to How to Use Radio Buttons. The listener is invoked after the selection has changed.

If the B button is selected, display a JOptionPane asking the user to confirm. Refer to How to Make Dialogs. A JOptionPane can also be closed by hitting the ESC key or pressing the X button in the top, right corner.

If the user closes the JOptionPane by clicking the YES button, we do nothing since button B is actually already selected. If the user closes the JOptionPane any other way, then we need to reset the selection to button A.

import java.awt.EventQueue;
import java.awt.event.ItemEvent;

import javax.swing.ButtonGroup;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JRadioButton;

public class Intercep {
    private JFrame frame;
    private JRadioButton aRadioButton;
    private JRadioButton bRadioButton;

    private void buildAndDisplayGui() {
        frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(createButtons());
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    private JPanel createButtons() {
        JPanel panel = new JPanel();
        ButtonGroup bg = new ButtonGroup();
        aRadioButton = new JRadioButton("A");
        bRadioButton = new JRadioButton("B");
        bRadioButton.addItemListener(this::handleItem);
        bg.add(aRadioButton);
        bg.add(bRadioButton);
        panel.add(aRadioButton);
        panel.add(bRadioButton);
        return panel;
    }

    private void handleItem(ItemEvent event) {
        if (event.getStateChange() == ItemEvent.SELECTED) {
            int result = JOptionPane.showConfirmDialog(frame,
                                                       "Are you sure?",
                                                       "Confirm",
                                                       JOptionPane.YES_NO_OPTION);
            switch (result) {
                case 0:
                    // YES
                    break;
                case -1:
                    // <ESC> or 'X'
                case 1:
                    // NO
                default:
                    aRadioButton.setSelected(true);
            }
        }
    }

    public static void main(String args[]) {
        EventQueue.invokeLater(() -> new Intercep().buildAndDisplayGui());
    }
}

Note this line in the above code:

bRadioButton.addItemListener(this::handleItem);

This is referred to as a method reference.