ComboBox Demo
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import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
/*
* ComboBoxDemo.java is a 1.4 application that 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() {
//Make sure we have nice window decorations.
JFrame.setDefaultLookAndFeelDecorated(true);
//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();
}
});
}
}
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