承继自JFrame，不显示内部容器

public class RootFrame extends JFrame {
	
	private static final long serialVersionUID = 1L;
	
	private JPanel centerPanel;
	
	@SuppressWarnings("unchecked")
	public RootFrame(String title) throws IOException{
		super();
		// setIconImages(new ICOFile(SourceLoader.AbsolutePath("files/images/menu/application.ico")).getImages());
		setTitle(title);
		setSize(400, 600);
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setLocationRelativeTo(null);
		menuBar();
		toolBar();
		center();
		statusBar();
		setVisible(true);
	}
	
	public void menuBar() {
		JMenuBar menuBar = new JMenuBar();
		JMenu config = new JMenu();
		config.setText("配置(Q)");
		config.setMnemonic('Q');
		
		JMenuItem switch_db = new JMenuItem();
		switch_db.setText("切换数据库(S)");
		switch_db.setMnemonic('S');
        // Image image = Toolkit.getDefaultToolkit().getImage(
				// getClass().getResource("/images/menu/搜狗浏览器截图.jpg"));
        // ImageIcon icon = new ImageIcon(image);
        // switch_db.setIcon(icon);
        switch_db.addActionListener(new Action());
        config.add(switch_db);
        menuBar.add(config);
        
        setJMenuBar(menuBar);
	}
	
	public void center() {
		// this.centerPanel = new JPanel();
		if(this.centerPanel == null) {
			this.centerPanel = new JPanel();
			// System.out.println("worec.form.RootFrame..center");
		}
		// System.out.println("worec.form.RootFrame..center");
		this.centerPanel.setLayout(new BorderLayout());
		JButton b = new JButton("1432");
		this.centerPanel.add(b);
		// this.centerPanel.setVisible(true);
		getContentPane().add(this.centerPanel, BorderLayout.CENTER);
	}
	
	public void toolBar() {
		
	}
	
	public void statusBar() {
		
	}
	
	public Component add(Component comp) {
		this.centerPanel.add(comp, BorderLayout.CENTER);
		// System.out.println("worec.form.RootFrame..add");
		// this.centerPanel.invalidate();