Tabbed pane does not appear when running Java swing app. nested classes approach

Question

I am using nested private classes to build a Java Swing application. The tabbedPane does not appear when running the application. When run, the application shows a blank frame. The app exits on close.

The main question is, what are the options to get the tabbedPane to appear? A second question is if nested classes are a good approach/ am I using them correctly?

The following are the relevant classes.

Constructor

package personalApp;

//imports

public class SwingApp {
//Attributes
//----- CONSTRUCTOR ------
SwingApp() throws IOException{
f1 = new Jframe();
 JTabbedPane z = new tabbedPane();
        f1.add(z);
        f1.setVisible(true);
        f1.setSize(400,400);
        f1.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
}

tabbedPane

   private class tabbedPane extends JTabbedPane {
        @Override
        public void setVisible(boolean aFlag) {
            super.setVisible(true);
        }

        @Override
        public Component add(String title, Component component) {
            super.add("Contacts", new panel2());
            return new panel2();
        }

    }

panel2

private class panel2 extends JPanel{

        @Override
        public void setLayout(LayoutManager mgr) {super.setLayout(new GridBagLayout());}

        @Override
        public void setBackground(Color bg) {super.setBackground(mainColor);}

        @Override
        public void setVisible(boolean aFlag) {super.setVisible(true);}

 public void add(Component comp, Object constraints) {
  //There is a JTable, JScrollPane(JTable),JToolbar and JButton added within this method. They all follow the same structure.
            openButtonPhonebook = new JButton("Open");
         //multiple lines of GridBagConstriants. c = GridBagconstraints.
            super.add(openButtonNotebook,c);
    }
}

Main

public static void main(String[] args) throws IOException {new SwingApp();}

I have tried adding the components in multiple add methods. This gives an error for overwriting the same method.

I have tried and was successful with adding components within the constructor method. This is causing the code to become hard to navigate. I want to use more abstraction to improve the readability of the code.

Ultimately, I am building a swing app with too much code to put in a constructor method. If there are alternatives to nested classes which improve readability, I am open to them.