import java.awt.*;import java.awt.event.*;import javax.swing.*;/* * RadioButtonDemo.java is a 1.4 application that requires these files: *   images/Bird.gif *   images/Cat.gif *   images/Dog.gif *   images/Rabbit.gif *   images/Pig.gif */public class RadioButtonDemo extends JPanel                             implements ActionListener {    static String birdString = "Bird";    static String catString = "Cat";    static String dogString = "Dog";    static String rabbitString = "Rabbit";    static String pigString = "Pig";    JLabel picture;    public RadioButtonDemo() {        super(new BorderLayout());        //Create the radio buttons.        JRadioButton birdButton = new JRadioButton(birdString);        birdButton.setMnemonic(KeyEvent.VK_B);        birdButton.setActionCommand(birdString);        birdButton.setSelected(true);        JRadioButton catButton = new JRadioButton(catString);        catButton.setMnemonic(KeyEvent.VK_C);        catButton.setActionCommand(catString);        JRadioButton dogButton = new JRadioButton(dogString);        dogButton.setMnemonic(KeyEvent.VK_D);        dogButton.setActionCommand(dogString);        JRadioButton rabbitButton = new JRadioButton(rabbitString);        rabbitButton.setMnemonic(KeyEvent.VK_R);        rabbitButton.setActionCommand(rabbitString);        JRadioButton pigButton = new JRadioButton(pigString);        pigButton.setMnemonic(KeyEvent.VK_P);        pigButton.setActionCommand(pigString);        //Group the radio buttons.        ButtonGroup group = new ButtonGroup();        group.add(birdButton);        group.add(catButton);        group.add(dogButton);        group.add(rabbitButton);        group.add(pigButton);        //Register a listener for the radio buttons.        birdButton.addActionListener(this);        catButton.addActionListener(this);        dogButton.addActionListener(this);        rabbitButton.addActionListener(this);        pigButton.addActionListener(this);        //Set up the picture label.        picture = new JLabel(createImageIcon("images/"                                             + birdString                                             + ".gif"));        //The preferred size is hard-coded to be the width of the        //widest image and the height of the tallest image.        //A real program would compute this.        picture.setPreferredSize(new Dimension(177, 122));        //Put the radio buttons in a column in a panel.        JPanel radioPanel = new JPanel(new GridLayout(0, 1));        radioPanel.add(birdButton);        radioPanel.add(catButton);        radioPanel.add(dogButton);        radioPanel.add(rabbitButton);        radioPanel.add(pigButton);        add(radioPanel, BorderLayout.LINE_START);        add(picture, BorderLayout.CENTER);        setBorder(BorderFactory.createEmptyBorder(20,20,20,20));    }    /** Listens to the radio buttons. */    public void actionPerformed(ActionEvent e) {        picture.setIcon(createImageIcon("images/"                                        + e.getActionCommand()                                        + ".gif"));    }    /** Returns an ImageIcon, or null if the path was invalid. */    protected static ImageIcon createImageIcon(String path) {        java.net.URL imgURL = RadioButtonDemo.class.getResource(path);        if (imgURL != null) {            return new ImageIcon(imgURL);        } else {            System.err.println("Couldn't find file: " + path);            return null;        }    }    /**     * Create the GUI and show it.  For thread safety,     * this method should be invoked from the     * event-dispatching thread.     */    private static void createAndShowGUI() {        //Make sure we have nice window decorations.        JFrame.setDefaultLookAndFeelDecorated(true);        //Create and set up the window.        JFrame frame = new JFrame("RadioButtonDemo");        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);        //Create and set up the content pane.        JComponent newContentPane = new RadioButtonDemo();        newContentPane.setOpaque(true); //content panes must be opaque        frame.setContentPane(newContentPane);        //Display the window.        frame.pack();        frame.setVisible(true);    }    public static void main(String[] args) {        //Schedule a job for the event-dispatching thread:        //creating and showing this application's GUI.        javax.swing.SwingUtilities.invokeLater(new Runnable() {            public void run() {                createAndShowGUI();            }        });    }}