Creating multiple panels in one frame

Question

Greetings,
As a newbie, I am sure you all have been in my place at one time or another so I will skip right to the meat of what I am trying to do.
I originally started out with GridBagLayout() and placing all my code in the main function declaration but that has it's limits.
I am trying to find a way to mount / add multiple panes onto one JPanel using functions in order to break up the code. I don't get an error when I compile, but the screen appears blank which tells me that I am adding one JPanel onto another in the wrong manner.
class PanelTest extends JFrame
  private JPanel mainPanel;
  private JPanel headerPanel;
  public void PanelTest()
    mainPanel = new JPanel(new BorderLayout());
    mainPanel.setLayout(new BoxLayout(mainPanel, BoxLayout.PAGE_AXIS));
    mainPanel.setBorder(BorderFactory.createEmptyBorder(5,5,5,5));
    mainPanel.setPreferredSize(new Dimension(400, 100));
    mainPanel.add(topPanel(), BorderLayout.NORTH);
    getContentPane().add(topPanel());
  private JPanel topPanel()
    headerPanel = new JPanel ();
    headerPanel.setPreferredSize(new Dimension (300, 50));
    headerPanel.setBorder(BorderFactory.createCompoundBorder(
            BorderFactory.createTitledBorder("Header Image"),
            BorderFactory.createEmptyBorder(5,5,5,5)));
    JLabel text = new JLabel("TEST");
    headerPanel.add(text);
    return headerPanel;
}I then use the following code in my main file to call and execute the code
class BerylMain extends JFrame
  public static void main(String args[])
     PanelTest panelTest = new PanelTest();
     panelTest.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
     panelTest.setSize(500, 400);
     panelTest.setVisible(true);
}I appreciate any advise on this.

Answer 1

public void PanelTest()  {
    /* try commenting this.
    mainPanel = new JPanel(new BorderLayout());
    mainPanel.setLayout(new BoxLayout(mainPanel, BoxLayout.PAGE_AXIS));
    mainPanel.setBorder(BorderFactory.createEmptyBorder(5,5,5,5));
    mainPanel.setPreferredSize(new Dimension(400, 100));
    mainPanel.add(topPanel(), BorderLayout.NORTH);
    getContentPane().add(topPanel());
}