public class Test extends JFrame
{
    private JPanel container;

    private JTextArea textArea;

    public Test() {
        setLayout(new BorderLayout());
        setUndecorated(true);

        container = new JPanel();
        textArea = new JTextArea("foo bar");

        final String key = "exitAction";

        final InputMap inputMap =
                rootPane.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW);
        inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_F12, 0), key);
        rootPane.getActionMap().put(key, new AbstractAction() {
            public void actionPerformed(ActionEvent e) {
                System.exit(0);
            }
        });

        container.add(textArea);
        getContentPane().add(container, BorderLayout.CENTER);
        setSize(400, 400);
        setLocationRelativeTo(null);
        setVisible(true);
    }

    public static void main(String[] a) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                new Test();
            }
        });
    }
}