Why won't the background color be filled with repaint(e)?

So I'm not sure what the problem is with the repaint method. It won't fill in a new background colour. It doesn't seem to print out a text within that method whenever I tried to debug it. I have 3 classes: GameInterface, Renderer, and RepaintConfiguration. The RepaintConfiguration extends from the GameInterface class and implements ActionListener.

public class GameInterface {

public static GameInterface gameInterface;   

public static JFrame jframe;

private String title;

private Container container;

public GameInterface() {
    gameInterface = this;
    jframe = new JFrame();
    jframe.setSize(1500, 800);
    jframe.setResizable(false);
    jframe.setTitle("Jetpack");
   
    jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    jframe.setVisible(true);
  } 
}
   

public class Renderer extends JPanel {

  
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        RepaintConfiguration.repaintConfiguration.repaint(g);
      }
}


public class RepaintConfiguration extends GameInterface implements ActionListener
{

    public static RepaintConfiguration repaintConfiguration;
    public static Renderer renderer;
   
    public static GameInterface gameInterface;
    

    public RepaintConfiguration() {
        super();
        repaintConfiguration = this;
        renderer = new Renderer();
        super.jframe.add(renderer);
   
        
        
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        renderer.repaint();
    }
    
    
    
    public void repaint(Graphics g) {
        g.setColor(Color.red);
        g.fillRect(0, 0, 1500, 800);
    }

    
}

I managed to get your code to compile and run. Public classes have to be inner classes.

I added a main method. I added a call to the SwingUtilities invokeLater method. This method ensures that the Swing components are created and executed on the Event Dispatch Thread.

I reordered the JFrame method calls. The JFrame methods must be called in a specific order. This is the order I use for all my Swing applications.

You don't size the JFrame. You size the drawing JPanel. The JFrame includes decorations that take up some space.

I left your convoluted drawing code. You're going to have great difficulties extending this code to actually create a game.

Here's the complete runnable code.

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class GameInterface {

    private JFrame jframe;

    private Renderer renderer;

    private RepaintConfiguration repaintConfiguration;
    
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new GameInterface();
            }
        });
    }

    public GameInterface() {
        this.repaintConfiguration = new RepaintConfiguration(this);

        jframe = new JFrame();
        jframe.setTitle("Jetpack");
        jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jframe.setResizable(false);

        this.renderer = new Renderer(repaintConfiguration);
        jframe.add(renderer, BorderLayout.CENTER);

        jframe.pack();
        jframe.setLocationByPlatform(true);
        jframe.setVisible(true);
    }

    public Renderer getRenderer() {
        return renderer;
    }

    public class Renderer extends JPanel {

        private static final long serialVersionUID = 1L;
        
        private RepaintConfiguration repaintConfiguration;

        public Renderer(RepaintConfiguration repaintConfiguration) {
            this.repaintConfiguration = repaintConfiguration;
            this.setPreferredSize(new Dimension(1500, 800));
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            repaintConfiguration.repaint(g);
        }
    }

    public class RepaintConfiguration implements ActionListener {

        private GameInterface gameInterface;

        public RepaintConfiguration(GameInterface gameInterface) {
            this.gameInterface = gameInterface;
        }

        @Override
        public void actionPerformed(ActionEvent event) {
            gameInterface.getRenderer().repaint();
        }

        public void repaint(Graphics g) {
            g.setColor(Color.red);
            g.fillRect(0, 0, 1500, 800);
        }

    }

}