将加速器描述添加到GUI中的JMenuItem，而无需实际添加加速器

Question

I'm trying to set some text to be displayed where the accelerator binding is usually displayed, for a JMenuItem . The demarcated Ctrl+Z text in the following image is an example of what I'm trying to set, for another JMenuItem .

I don't actually want to set an accelerator for this JMenuItem , though. I've poked around the source for several classes, like JMenuItem and BasicMenuItemUI , to no avail. What's the simplest way to achieve this?

Thanks in advance :)

Answer 1

I assume the reason you want this is so you can prevent the menu from triggering the undo action a second time, when the key combination is already bound on a component on the frame, but this shouldn't be necessary. If the component consumes the key event, the menu won't detect it.

Here's an example with a JTextArea to see what I mean:

JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

JMenuBar menu = new JMenuBar();
frame.setJMenuBar(menu);
JMenu menuEdit = new JMenu("Edit");
menu.add(menuEdit);
JMenuItem menuEditUndo = new JMenuItem("Undo");
menuEdit.add(menuEditUndo);
menuEditUndo.setAccelerator(KeyStroke.getKeyStroke("control Z"));
menuEditUndo.addActionListener(new ActionListener() {
    @Override
    public void actionPerformed(ActionEvent e) {
        System.out.println("menu");
    }
});

JTextArea textArea = new JTextArea(20, 40);
textArea.getInputMap().put(KeyStroke.getKeyStroke("control Z"), "undo");
textArea.getActionMap().put("undo", new AbstractAction() {
    @Override
    public void actionPerformed(ActionEvent e) {
        System.out.println("text");
    }
});
frame.add(new JScrollPane(textArea));

frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);

Both the text area and the menu item have bound to the same key combo, but pressing Ctrl+Z while the text area has focus prints only "text" and never "menu". Ie, the action does not happen twice. Although this uses a JTextArea, it should be true of any component.