ActionListener Help

Question

Hi
I am creating a very basic program that has two buttons and a text field. When any button is clicked, then the text in the text field should change. However, I've run into a problem with the actionPerformed method - it doesn't seem to recognise the names of my buttons i.e. *'+button_name +cannot be resolved'*. So, when I click the button then nothing happens. The code is not very large so I'll provide it below.
import javax.swing.*;*
import java.awt.event.;
import java.awt.*;
public class SGUI extends JPanel implements ActionListener{
public SGUI() {
ImageIcon hello = createImageIcon("images/hello.gif");
ImageIcon bye = createImageIcon("images/bye.gif");
JButton sayHello = new JButton(hello);
JButton sayBye = new JButton(bye);
JTextField message = new JTextField("What shall I say?");
message.setBackground(Color.blue);
message.setForeground(Color.WHITE);
//Listen for actions on the 2 buttons and text field.
sayHello.addActionListener(this);
sayBye.addActionListener(this);
message.addActionListener(this);
sayHello.setToolTipText("display greeting");
sayBye.setToolTipText("display farewell");
//add components to container using flowLayout
add(sayHello);
add(sayBye);
add(message);
public void actionPerformed(ActionEvent ae){
if (ae.getSource()==sayHello){
message.setText("Hello!");
} //respond to the button pressed
protected static ImageIcon createImageIcon(String path) {
java.net.URL imgURL = SGUI.class.getResource(path);
if (imgURL != null) {
return new ImageIcon(imgURL);
} else {
System.err.println("Couldn't find file: " + path);
return null;
private static void createAndShowGUI() {
//Create and set up the window.
JFrame frame = new JFrame("HelloGoodbye");
//Create and set up the content pane.
SGUI newContentPane = new SGUI();
newContentPane.setOpaque(true); //content panes must be opaque
newContentPane.setBackground(Color.yellow);
frame.setContentPane(newContentPane);
//Display the window.
frame.pack();
frame.setSize(300, 300);
frame.setVisible(true);
//run the program
public static void main(String[] args) {
createAndShowGUI();
}The _{color:#ff0000}red lines{color}_ appear underneath sayBye+ and message in the actionPerformed() method, which results in the actionPerformed method not working - although the actual program still runs*. Please help!
Edited by: aras298 on May 5, 2008 8:49 AM

Answer 1

you appear to have a problem of scope: your JButtons are declared and defined in the constructor and have a scope that is confined to the constructor. Anything that's outside of the constructor will thus not be able to "see" these components. One solution: make the buttons declared in the class. You can still construct them in the constructor, but make sure that their scope is the entire class, not just the constructor.
Also, I recommend that you start getting in the habit of not having your main GUI classes implement the ActionListener interface, but rather using anonymous inner classes, or private inner classes, or stand-alone classes for your actionlisteners. It's much cleaner this way.