你必须致电

 private JFrame frame = new JFrame();
 ...
 ...
 frame.getContentPane().removeAll();
 frame.repaint();

removeAll（）尚未被覆盖为 add（）或 remove（）转发到 contentPane 必要时。

removeAll() has not been overridden as add() or remove() to forward to the contentPane as necessary.