Re: ActionListener

Knute Johnson <>
Sat, 01 Dec 2007 18:26:31 -0800

By top posting he means not to put the content of your new post on top
of the old post. Frankly I don't care but I know you will get unending
grief if you don't.

As to your code. I was not able to compile it because it was missing
several pieces so we will ignore that for the moment. ActionListeners
consume a lot of memory and you usually only need one so I would go with
one. When you create a button and add an ActionListener to it, it will
default to using the text of the button as its actionCommand. So your
button looks like this;

JButton b = new JButton("Press Me");

Your action listener then tests the action command to branch to the
appropriate code;

ActionListener al = new ActionListener() {
     public void actionPerformed(ActionEvent ae) {
         String ac = ae.getActionCommand();

         if (ac.equals("Press Me")) {
             // do this
         } else if (ac.equals("Quit")) {
             // do that

I like to set up my main class as an ActionListener implementor;

public class MainClass extends Whatever implements ActionListener {

So in my MainClass I have to have a method;

     public void actionPerformed(ActionEvent ae) {

Then when I create my buttons I just;

     JButton b = new JButton("Press Me");

So your question on how to get to the variable in multiple
ActionListeners or methods?

public class MyClass extends JFrame implements ActionListener {
     private int seeEveryWhereIndex;

     // a lot of other stuff

     // gui code
     JButton b = new JButton("Decrement");

     b = new JButton("Increment");

     // other stuff

     public void actionPerformed(ActionEvent ae) {
         String ac = ae.getActionCommand();

         if (ac.equals("Decrement")) {
         } else if (ac.equals("Increment")) {

Putting your "seeEveryWhere" variable where we have it here makes it
visible to your whole class.

One other thing that will make your life easier (as well as the folks
who try to help you on this list) is to indent your source code like
mine is above. It makes it much easier to read. There are also some
recommended standards for variable and class names.

These just make it easier for others to know what you are up to.

Unless my program is really large or I'm going to use the same code
multiple times, I like to build my GUI in a primary container. In your
example above, I would put my GUI code in the StudentTest?? class.

A simple example below;

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class test extends JFrame implements ActionListener {
     private int index;
     private JLabel label;

     public test() {

         setLayout(new GridBagLayout());

         GridBagConstraints c = new GridBagConstraints();
         c.insets = new Insets(2,2,2,2);
         c.gridx = 0;

         label = new JLabel(Integer.toString(index));

         JButton b = new JButton("Increment");

         b = new JButton("Decrement");


     public void actionPerformed(ActionEvent ae) {
         String ac = ae.getActionCommand();

         if (ac.equals("Increment")) {
         } else if (ac.equals("Decrement")) {

     public static void main(String[] args) {
         EventQueue.invokeLater(new Runnable() {
             public void run() {
                 new test();


Knute Johnson
email s/nospam/knute/

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