[Fou-Lu]

You can listen for the events and respond accordingly, but its probably easier to just set the DocumentFilter. Here's a quick example using an anonymous class:

PHP Code:

    public static void main(String... argv)
    {
        JFrame f = new JFrame();
        JTextField field = new JTextField();

        if (field.getDocument() instanceof AbstractDocument)
        {
            ((AbstractDocument) field.getDocument()).setDocumentFilter(new DocumentFilter()
            {
                public void replace(FilterBypass fb, int offs, int length, String str, AttributeSet a) throws BadLocationException
                {
                    try
                    {
                        Integer.parseInt(str);
                        super.replace(fb, offs, length, str, a);
                    }
                    catch (NumberFormatException ex)
                    {
                        // Don't care, just abandon it.
                    }
                }
            });
        }
        f.add(field);
        f.pack();
        f.setVisible(true);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }