Java: 在JPanel上获得焦点并且使用键盘事件

Java: 在JPanel上获得焦点并且使用键盘事件
        this.addKeyListener(new KeyAdapter() {
            @Override
            public void keyPressed(KeyEvent e) {
                System.out.println(e.getKeyChar() + ", " + e.getKeyCode()
                        + ", " + KeyEvent.getKeyText(e.getKeyCode())
                        + ", isActionKey: " + e.isActionKey());
            }
        });

    private static void createAndShowGUI() {
        JFrame frame = new JFrame("Frame");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(400, 400);

        JPanel test = new Test();
        frame.getContentPane().add(test);

        frame.setVisible(true);
        test.requestFocus(); // 注意,与上面的这一句不能反