package components; import java.awt.*; import java.awt.event.*; import javax.swing.*; /* * ComboBoxDemo.java uses these additional files: * images/Bird.gif * images/Cat.gif * images/Dog.gif * images/Rabbit.gif * images/Pig.gif */ public class ComboBoxDemo extends JPanel implements ActionListener { JLabel picture; public ComboBoxDemo() { super(new BorderLayout()); String[] petStrings = { "Bird", "Cat", "Dog", "Rabbit", "Pig" }; //Create the combo box, select the item at index 4. //Indices start at 0, so 4 specifies the pig. JComboBox petList = new JComboBox(petStrings); petList.setSelectedIndex(4); petList.addActionListener(this); //Set up the picture. picture = new JLabel(); picture.setFont(picture.getFont().deriveFont(Font.ITALIC)); picture.setHorizontalAlignment(JLabel.CENTER); updateLabel(petStrings[petList.getSelectedIndex()]); picture.setBorder(BorderFactory.createEmptyBorder(10,0,0,0)); //The preferred size is hard-coded to be the width of the //widest image and the height of the tallest image + the border. //A real program would compute this. picture.setPreferredSize(new Dimension(177, 122+10)); //Lay out the demo. add(petList, BorderLayout.PAGE_START); add(picture, BorderLayout.PAGE_END); setBorder(BorderFactory.createEmptyBorder(20,20,20,20)); } /** Listens to the combo box. */ public void actionPerformed(ActionEvent e) { JComboBox cb = (JComboBox)e.getSource(); String petName = (String)cb.getSelectedItem(); updateLabel(petName); } protected void updateLabel(String name) { ImageIcon icon = createImageIcon("images/" + name + ".gif"); picture.setIcon(icon); picture.setToolTipText("A drawing of a " + name.toLowerCase()); if (icon != null) { picture.setText(null); } else { picture.setText("Image not found"); } } /** Returns an ImageIcon, or null if the path was invalid. */ protected static ImageIcon createImageIcon(String path) { java.net.URL imgURL = ComboBoxDemo.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() { //Create and set up the window. JFrame frame = new JFrame("ComboBoxDemo"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); //Create and set up the content pane. JComponent newContentPane = new ComboBoxDemo(); 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(); } }); } }