这段代码有什么问题吗?
JFrame frame = new JFrame();
JPanel panel = new JPanel();
panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
JLabel lab = new JLabel();
lab.setHorizontalAlignment(SwingConstants.CENTER);
lab.setText("TESET");
panel.add(lab);
frame.getContentPane().add(BorderLayout.NORTH,panel);
frame.setVisible(true);
frame.pack();