Of course! Here is a comprehensive guide to using JRadioButton in Java, covering everything from basic creation to handling events and using them in groups.

What is a JRadioButton?

A JRadioButton is a graphical component that allows the user to select one option from a set. When a radio button is selected, any previously selected radio button in the same group is automatically deselected. This "one-of-many" behavior is its defining characteristic.

Key Concepts:

1. Grouping: Radio buttons must be placed in a ButtonGroup to enforce the "one selection only" rule. A ButtonGroup is a logical grouping, not a visual one. It's just a container that manages the state of its buttons.
2. Visual Appearance: You typically place radio buttons inside a container like a JPanel to arrange them visually on the screen.
3. Selection: You can check if a radio button is selected using its isSelected() method and set its selection using setSelected(true).

Basic Example: Creating and Grouping Radio Buttons

This is the simplest example showing how to create two radio buttons, group them, and add them to a window.

import javax.swing.*;
import java.awt.*;
public class SimpleRadioButtonExample {
    public static void main(String[] args) {
        // Create the main window
        JFrame frame = new JFrame("Simple Radio Button Example");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(300, 150);
        frame.setLayout(new FlowLayout()); // Use a simple layout
        // 1. Create the radio button instances
        JRadioButton option1 = new JRadioButton("Option 1");
        JRadioButton option2 = new JRadioButton("Option 2");
        // 2. Create a ButtonGroup and add the radio buttons to it
        // This ensures only one can be selected at a time
        ButtonGroup group = new ButtonGroup();
        group.add(option1);
        group.add(option2);
        // 3. (Optional) Set a default selection
        option1.setSelected(true); // Select "Option 1" by default
        // 4. Add the radio buttons to the frame's content pane
        frame.add(option1);
        frame.add(option2);
        // Display the window
        frame.setVisible(true);
    }
}

Explanation:

• JRadioButton("Option 1"): Creates a radio button with the specified text label.
• ButtonGroup(): Creates an empty group.
• group.add(option1): Adds the radio button to the group. This is the crucial step for the "one selection only" behavior.
• option1.setSelected(true): Programmatically selects the first option when the window appears.
• frame.add(...): Adds the buttons to the window so they are visible.

Handling User Selections (Event Handling)

You often need to know which option the user has selected. This is done using an ActionListener.

The ActionEvent's getActionCommand() method returns the text label of the selected button. A better practice is to use setActionCommand() to give each button a unique, program-friendly identifier.

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class RadioButtonEventExample {
    public static void main(String[] args) {
        JFrame frame = new JFrame("Radio Button Event Handling");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(350, 150);
        frame.setLayout(new FlowLayout());
        // Create radio buttons
        JRadioButton teaButton = new JRadioButton("Tea");
        JRadioButton coffeeButton = new JRadioButton("Coffee");
        JRadioButton juiceButton = new JRadioButton("Juice");
        // Group them
        ButtonGroup drinkGroup = new ButtonGroup();
        drinkGroup.add(teaButton);
        drinkGroup.add(coffeeButton);
        drinkGroup.add(juiceButton);
        // Set a default selection
        teaButton.setSelected(true);
        // Add an ActionListener to the group
        // The listener will be triggered whenever any button in the group is selected
        ActionListener listener = new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                // Get the action command we set earlier
                String selectedDrink = e.getActionCommand();
                System.out.println("Selected drink: " + selectedDrink);
                // You can also use a switch statement for more complex logic
                switch (selectedDrink) {
                    case "tea":
                        System.out.println("Preparing a nice cup of tea...");
                        break;
                    case "coffee":
                        System.out.println("Brewing some coffee...");
                        break;
                    case "juice":
                        System.out.println("Squeezing some fresh juice...");
                        break;
                }
            }
        };
        // Set action commands and add the listener to each button
        teaButton.setActionCommand("tea");
        coffeeButton.setActionCommand("coffee");
        juiceButton.setActionCommand("juice");
        teaButton.addActionListener(listener);
        coffeeButton.addActionListener(listener);
        juiceButton.addActionListener(listener);
        // Add buttons to the frame
        frame.add(teaButton);
        frame.add(coffeeButton);
        frame.add(juiceButton);
        frame.setVisible(true);
    }
}

Explanation:

• setActionCommand("tea"): Associates a specific string with the button. This string is sent with the ActionEvent when the button is selected, making it easy to identify the source in the listener.
• addActionListener(listener): Attaches the same listener to all buttons. When any button is clicked, its actionPerformed method will be called.
• e.getActionCommand(): Retrieves the string we set with setActionCommand.

Complete Example: Getting a Value from a GUI

This is a more practical example where radio buttons are used in a small application to get a user's choice and display a message.

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class CompleteRadioButtonExample {
    public static void main(String[] args) {
        // 1. Create the main frame
        JFrame frame = new JFrame("Shipping Options");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(400, 250);
        frame.setLayout(new BorderLayout());
        // 2. Create a panel for the radio buttons
        JPanel radioPanel = new JPanel(new GridLayout(0, 1)); // Vertical layout
        radioPanel.setBorder(BorderFactory.createTitledBorder("Choose Shipping:"));
        // 3. Create radio buttons
        JRadioButton freeShipping = new JRadioButton("Free Shipping (5-7 days)");
        JRadioButton standardShipping = new JRadioButton("Standard Shipping (2-3 days)");
        JRadioButton expressShipping = new JRadioButton("Express Shipping (1-2 days)");
        // 4. Group the radio buttons
        ButtonGroup shippingGroup = new ButtonGroup();
        shippingGroup.add(freeShipping);
        shippingGroup.add(standardShipping);
        shippingGroup.add(expressShipping);
        // 5. Set a default selection
        freeShipping.setSelected(true);
        // 6. Add buttons to the radio panel
        radioPanel.add(freeShipping);
        radioPanel.add(standardShipping);
        radioPanel.add(expressShipping);
        // 7. Create a panel for the button and label
        JPanel bottomPanel = new JPanel(new FlowLayout());
        JButton confirmButton = new JButton("Confirm Selection");
        JLabel resultLabel = new JLabel("Please select a shipping option.");
        // 8. Add action listener to the confirm button
        confirmButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                String message = "No option selected.";
                if (expressShipping.isSelected()) {
                    message = "You selected: Express Shipping. It will arrive in 1-2 days.";
                } else if (standardShipping.isSelected()) {
                    message = "You selected: Standard Shipping. It will arrive in 2-3 days.";
                } else if (freeShipping.isSelected()) {
                    message = "You selected: Free Shipping. It will arrive in 5-7 days.";
                }
                resultLabel.setText(message);
            }
        });
        bottomPanel.add(confirmButton);
        bottomPanel.add(resultLabel);
        // 9. Add panels to the main frame
        frame.add(radioPanel, BorderLayout.CENTER);
        frame.add(bottomPanel, BorderLayout.SOUTH);
        // Display the window
        frame.setVisible(true);
    }
}

Summary of Key Methods