Why is the JButton is not taking up the whole screen?

I just started using Java Swing and GridBagLayout, and I can't figure out how to get the button to take up all of the space I'm trying to give it (the whole window in this case). I apologize if my code looks bad, I only do Java as a hobby and I don't have formal training.

Here is the code from Main.java:

gui = new Gui();
gui.textButton("Hello World!", 1.0, 1.0, 0, 0, 1, 1);

Here is the code from Gui.java:

public class Gui extends JFrame {


    private static GridBagLayout gbl = new GridBagLayout();
    public JPanel panel = new JPanel();


    public Gui() {


        this.setExtendedState(JFrame.MAXIMIZED_BOTH);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);


        this.setTitle("Conlang Translator");
        this.setIconImage(new ImageIcon("images\\icon.png").getImage());

        
        this.setLayout(gbl);
        this.add(panel);
        this.setVisible(true);
    }


    public JButton textButton(String text, double weightx, double weighty, int gridx, int gridy, int gridwidth, int gridheight) {

    
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.weightx = weightx;
        gbc.weighty = weighty;
        gbc.gridx = gridx;
        gbc.gridy = gridy;
        gbc.gridwidth = gridwidth;
        gbc.gridheight = gridheight;
        gbc.fill = GridBagConstraints.BOTH;


        JButton button = new JButton(text);
        panel.add(button, gbc);
        panel.revalidate();
        panel.repaint();
        return button;
    }
}

The immediate solution would be to replace this.setLayout(gbl) with panel.setLayout(gbl), for example...

import java.awt.EventQueue;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Main {

    public static void main(String[] args) {
        new Main();
    }

    public Main() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                Gui gui = new Gui();
                gui.textButton("Hello World!", 1.0, 1.0, 0, 0, 1, 1);
                gui.pack();
                gui.setLocationRelativeTo(null);
                gui.setVisible(true);
            }
        });
    }

    public class Gui extends JFrame {

        private static GridBagLayout gbl = new GridBagLayout();
        public JPanel panel = new JPanel();

        public Gui() {

            //this.setExtendedState(JFrame.MAXIMIZED_BOTH);
            //this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

            this.setTitle("Conlang Translator");
            this.setIconImage(new ImageIcon("images\\icon.png").getImage());

            //this.setLayout(gbl);
            panel.setLayout(gbl);
            this.add(panel);
            this.setVisible(true);
        }

        public JButton textButton(String text, double weightx, double weighty, int gridx, int gridy, int gridwidth, int gridheight) {

            GridBagConstraints gbc = new GridBagConstraints();
            gbc.weightx = weightx;
            gbc.weighty = weighty;
            gbc.gridx = gridx;
            gbc.gridy = gridy;
            gbc.gridwidth = gridwidth;
            gbc.gridheight = gridheight;
            gbc.fill = GridBagConstraints.BOTH;

            JButton button = new JButton(text);
            panel.add(button, gbc);
            panel.revalidate();
            panel.repaint();
            return button;
        }
    }
}

As already stated, you could get the same effect by using a BorderLayout, but I'm assuming that you have reasons for wanting to use a GridBagLayout