BorderLayout中嵌套JPanel无法显示组件

[流光_]

在JFrame的子类中使用了CardLayout来管理四个JPanel子类，而在其中一个子类中，用了BorderLayout来布局，并在BorderLayout中的每一个部分使用了JPanel；这样设置后所有的组件都无法显示。

JFrame 子类：

public class Frame extends JFrame implements PanelSwitch {

    private static final long serialVersionUID = -1629925106866926779L;

    private static final String CARD_HOME = "home";
    private static final String CARD_ROLECALL = "roleCall";
    private static final String CARD_SESSION = "session";
    private static final String CARD_SETTING = "setting";

    private JPanel homePanel;
    private JPanel rolecallPanel;
    private JPanel sessionPanel;
    private JPanel settingPanel;

    private JPanel mainPanel = new JPanel();

    private CardLayout layout = new CardLayout();

    private Conference conference;

    public Frame() {

        homePanel = new HomePanel(this);
        rolecallPanel = new RolecallPanel(this);
        sessionPanel = new SessionPanel(this);
        settingPanel = new SessionPanel(this);

        initFrame();

    }

    private void initFrame() {
        setLayout(layout);

        add(homePanel, CARD_HOME);
        add(rolecallPanel, CARD_ROLECALL);
        add(sessionPanel, CARD_SESSION);
        add(settingPanel, CARD_SETTING);

        setVisible(true);
    }

    public void switch_rolecallPanel() {
        layout.show(this, CARD_ROLECALL);
    }

    public void switch_sessionPanel() {
        layout.show(this, CARD_SESSION);
    }

    public void switch_homePanel() {
        layout.show(this, CARD_HOME);
    }

    public void switch_settingPanel() {
        layout.show(this, CARD_SETTING);
    }

    public static void main(String [] args) {
        SwingConsole.run(new Frame());
        // 一个辅助类，用于设置JFrame的title, height, width等属性
    }
}

JPanel 子类

public class HomePanel extends JPanel {

    private static final long serialVersionUID = -2977633553899021068L;

    private JLabel la_ConfName;
    private JLabel la_ConfTopic;
    private PanelSwitch frame;

    private JButton bt_roleCallStart;
    private JButton bt_settings;

    private ActionListener lis_roleCallStart = new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            frame.switch_rolecallPanel();
        }
    };

    private ActionListener lis_settings = new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            frame.switch_settingPanel();
        }
    };

    private Conference conferenceSetting;

    private BorderLayout layout = new BorderLayout();

    public HomePanel(PanelSwitch frame) {
        this.frame = frame;

        initTextField();
        initButtons();
        initProductInfo();

        setLayout(layout);
        setVisible(true);
        validate();
    }

    private void initTextField() {
        la_ConfName = new JLabel();
        la_ConfName.setFont(GraphicsConfig.getTitleFont());
        la_ConfName.setVisible(true);

        la_ConfTopic = new JLabel();
        la_ConfTopic.setFont(GraphicsConfig.getTitleFont());
        la_ConfTopic.setVisible(true);

        //// FIXME: 7/30/16
//        la_ConfName.setText(conferenceSetting.getName());
        la_ConfName.setText("Title");
//        la_ConfTopic.setText(conferenceSetting.getTopic());
        la_ConfTopic.setText("subTitle");

        JPanel confInfo = new JPanel();
        confInfo.setLayout(new FlowLayout());
        confInfo.add(la_ConfName);
        confInfo.add(la_ConfTopic);
        confInfo.setVisible(true);
        confInfo.validate();
        add(confInfo, BorderLayout.NORTH);
    }

    private void initButtons() {
        bt_roleCallStart = new JButton("Start Session");
        bt_roleCallStart.addActionListener(lis_roleCallStart);
//        bt_roleCallStart.setVisible(true);

        bt_settings = new JButton("Settings");
        bt_settings.addActionListener(lis_settings);
//        bt_roleCallStart.setVisible(true);

        JPanel buttons = new JPanel();
        buttons.setLayout(new BoxLayout(buttons, BoxLayout.Y_AXIS));
        buttons.add(bt_settings);
        buttons.add(Box.createVerticalStrut(12));
        buttons.add(bt_roleCallStart);
        buttons.setVisible(true);
        buttons.validate();
        add(buttons, BorderLayout.EAST);
    }

    private void initProductInfo() {
        JLabel groupInfo = new JLabel("Product designed by");
        JLabel groupPhoto = new JLabel(new ImageIcon(getClass().getResource("/logo/logo.jpg")));

        JPanel info = new JPanel();
        info.setLayout(new BoxLayout(info, BoxLayout.Y_AXIS));
        info.add(groupInfo);
        info.add(Box.createVerticalGlue());
        info.add(groupPhoto);
        info.setVisible(true);
        info.validate();
        add(info, BorderLayout.WEST);
    }
}