Re: Applet - Creating new objects from a Button Listener

Tom Hawtin <>
Mon, 23 Apr 2007 00:25:26 +0100
theneb wrote:

Hello everyone, I'm attempting to create JComponents from when a
button is clicked. However I'm assuming I'm missing something? (Or
it's not possible)

 From the java.awt.Container.add API docs:

"Note: If a component has been added to a container that has been
displayed, validate must be called on that container to display the new
component. If multiple components are being added, you can improve
efficiency by calling validate only once, after all the components have
been added."

public class myApplet extends Applet implements ActionListener{

Much better to use anonymous inner classes for listeners, otherwise you
will have a mess. (And initial caps for type names.)

 > private HashMap<String,testButton> buttons;

This can just be Map.

 > buttons.put(String.valueOf(buttons.size()),new testButton());
 > buttonPanel.add(buttons.get(String.valueOf(buttons.size()-1)));

That's just confusing.

     public void actionPerformed(ActionEvent event) {

Never used...

private class testButton extends JButton implements ActionListener{

Again, don't do listeners like that. And you don't need to extend
JButton at all.

public class MyApplet extends Applet {

     private final Map<String,JButton> buttons =
         new HashMap<String,JButton>();

     private JPanel buttonPanel;

     public void init() {
         buttonPanel = new JPanel();

     private void addButton() {
          String id = String.valueOf(buttons.size());
          JButton button = new JButton(id);
          button.addActionListener(new ActionListener {
                  public void actionPerformed(ActionEvent event) {
          buttons.put(id, button);

(Disclaimer: Not compiled or tested.)

Tom Hawtin

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