Enabling/Disabling menuitems in a JMenu

Question

Hi,
The application I'm developing has a JMenu, like any other Swing app
out there. The menuitems in that JMenu are enabled/disabled according
to the state of the app. I'd like to know which is the best way to
enable or disable the individual JMenuItems from any point in the
app, do I have to hold a global pointer to every JMenuItem in the
app and call setEnable() ? Or can I send a change event which
is captured by a hypothetical enablelistener registered in
every menu item ?
thanks in advance

Answer 1

Okay, here's a skeleton of working with actions and a Document/Listener pattern.
Here are the core classes:
import java.io.*;
import java.util.*;
import javax.swing.*;
public interface DocModel {
    public class Event extends EventObject {
        public enum Type {DOC_OPENED, DOC_CLOSED};
        public Event(DocModel model, Type type) {
            super(model);
            this.type = type;
        public final Type getType() {
            return type;
        private final Type type;
    public interface Listener extends EventListener {
        public void docOpened(Event event);
        public void docClosed(Event event);
    public void addDocListener(Listener l);
    public void removeDocListener(Listener l);
    public void open(File file) throws IOException;
    public void play();
    public void close();
    public JComponent createView();
}You don't have to nest types, but I like to.
Here is an abstract class the lets EventListenerList do all the work (I copyied and pasted the code from the API.)
import java.io.*;
import javax.swing.event.*;
public abstract class AbstractDocModel implements DocModel {
    private EventListenerList listenerList = new EventListenerList();
    protected void fireDocOpened() {
        Object[] listeners = listenerList.getListenerList();
        Event evt = new Event(this, Event.Type.DOC_OPENED);
        for (int i = listeners.length-2; i>=0; i-=2) {
            if (listeners==Listener.class)
((Listener)listeners[i+1]).docOpened(evt);
protected void fireDocClosed() {
Object[] listeners = listenerList.getListenerList();
Event evt = new Event(this, Event.Type.DOC_CLOSED);
for (int i = listeners.length-2; i>=0; i-=2) {
if (listeners[i]==Listener.class)
((Listener)listeners[i+1]).docClosed(evt);
public void addDocListener(Listener l) {
listenerList.add(Listener.class, l);
public void removeDocListener(Listener l) {
listenerList.remove(Listener.class, l);
public void open(File file) throws IOException {
fireDocOpened();
public void close() {
fireDocClosed();
Here is a simple implementation with Actions. I didn't have to make the actions DocListeners as well --
that's overkill, I could have adjusted their enabled state in open/play/close, but I wanted to demonstrate
letting listeners keep themselves in synch.
import java.awt.event.*;
import java.io.*;
import javax.swing.*;
import javax.swing.text.*;
public class SimpleDocModel extends AbstractDocModel {
    private Document document = new PlainDocument();
    private class OpenAction extends AbstractAction implements DocModel.Listener {
        public OpenAction() {
            super("open");
        public void actionPerformed(ActionEvent evt) {
            try {//find file
                File file = new File("bogus");
                open(file);
            } catch (IOException e) {
                //report it...
        public void docOpened(Event event) {
            setEnabled(false);
        public void docClosed(Event event) {
            setEnabled(true);
    private OpenAction openAction = new OpenAction();
    private class PlayAction extends AbstractAction implements DocModel.Listener {
        public PlayAction()
        {   super("play");
            setEnabled(false);
        public void actionPerformed(ActionEvent evt) {
            play();
        public void docOpened(Event event) {
            setEnabled(true);
        public void docClosed(Event event) {
            setEnabled(false);
    private PlayAction playAction = new PlayAction();
    private class CloseAction extends AbstractAction implements DocModel.Listener {
        public CloseAction()
        {   super("close");
            setEnabled(false);
        public void actionPerformed(ActionEvent evt) {
            close();
        public void docOpened(Event event) {
            setEnabled(true);
        public void docClosed(Event event) {
            setEnabled(false);
    private CloseAction closeAction = new CloseAction();
    public SimpleDocModel() {
        setMessage("empty doc");
        addDocListener(openAction);
        addDocListener(playAction);
        addDocListener(closeAction);
    public void addToToolBar(JToolBar tb) {
        tb.add(openAction);
        tb.add(closeAction);
        tb.add(playAction);
    public void open(File file) throws IOException {
        setMessage("file opened");
        super.open(file);
    public void close() {
        setMessage("closed");
        super.close();
    public void play() {
        setMessage("playing continuously");
    public JComponent createView() {
        JTextField view = new JTextField();
        view.setDocument(document);
        view.setEditable(false);
        return view;
    private void setMessage(String message) {
        try {
            document.remove(0, document.getLength());
            document.insertString(0, message, null);
        } catch (BadLocationException e) {
            e.printStackTrace();
}Are you still with me? Run this code:
import java.awt.*;
import javax.swing.*;
public class SampleApp {
    JFrame frame = new JFrame("Sample App");
    SimpleDocModel model = new SimpleDocModel();
    public SampleApp () {
        JToolBar tb = new JToolBar();
        model.addToToolBar(tb);
        Container cp = frame.getContentPane();
        cp.add(tb, BorderLayout.NORTH);
        cp.add(model.createView(), BorderLayout.SOUTH);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    public static void main(String[] args) {
        new SampleApp();