Java SE (Java Platform, Standard Edition)

I'm trying to learn the GridBagLayout and I've come across a small problem. I've got a JFrame, and I want to add a tabbed pane to it and a couple of buttons.
For some reason, my JMenuBar doesn't appear on the screen..... If anyone could point me in the direction of what I'm doing wrong, that would be great.
Here's my code:

Set up the menu:

private void initComponents(){
        // Set up the menus
        menuBar = new JMenuBar();

        // File Menu
        JMenu menu = new JMenu("File");
        JMenuItem item = new JMenuItem("New");
        item.addActionListener(new ActionListener(){

            @Override
            public void actionPerformed(ActionEvent arg0) {
                // TODO Auto-generated method stub

            }

        });
        menu.add(item);

        buildComponents();
}

build components

private void buildComponents(){
        //Build the Main Window

        int width=(int)Toolkit.getDefaultToolkit().getScreenSize().getWidth();
        int height=(int)Toolkit.getDefaultToolkit().getScreenSize().getHeight();
        this.setSize(width,height);

        //this.setMenuBar(menuBar);

        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        Container mainContainer = this.getContentPane();
        mainContainer.setLayout(new GridBagLayout());
        GridBagConstraints c = new GridBagConstraints();

        this.setJMenuBar(menuBar);

        c.anchor = GridBagConstraints.FIRST_LINE_START;
        c.fill = GridBagConstraints.HORIZONTAL;
        c.gridx = 0;
        c.gridy = 1;
        mainContainer.add(tabPanel,c);

        c.anchor = GridBagConstraints.PAGE_END;
        c.weightx = 0;
        c.weighty = 0;
        c.fill = GridBagConstraints.NONE;
        c.gridx = 1;
        c.gridy = 2;
        mainContainer.add(back,c);

        c.gridx = 2;
        mainContainer.add(next,c);

        this.setVisible(true);

    }