I want to make a programm in java that dropps a square at the position of your mouse. For that I wanted to draw a grid as background and then add the squares but as soon as I add a new component to the JFrame the background disappers. This also happens the other way around so if I add a Square and then add the Background the square disappers. The following is the code. My Question is now how I can add the second Graphic without the first one disapiring. I’m also sorry if my english isn’t that great it is not my native language.

import java.awt.BorderLayout;
import java.awt.Image;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.WindowConstants;

//Mainmethod
public class App {
    public static void main(String[] args) throws Exception {
        System.out.println("Hello World");
        MainFrame myFrame = new MainFrame();
        myFrame.init(); 
    }
}
//Window
public class MainFrame extends JFrame{
    public void init(){
        Image Logo; // Image for the window icon
        JPanel contentPane;
        Background background = new Background();
        Sand sand = new Sand();

        try {//sets the WidnowIcon
            Logo = ImageIO.read(new File("Logo.jpg"));
            setIconImage(Logo);
        } catch (IOException e) {
            
            e.printStackTrace();
        }
        //JFrameconfiguratio     
        setTitle("Sandsim");
        setSize(600, 600);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setVisible(true);

        //contentPaneconfiguration
        contentPane = new JPanel();
        contentPane.setLayout(new BorderLayout());
        contentPane.setVisible(true);
        setContentPane(contentPane);

        //adds Background and sand but you can only see the one that was added last
        contentPane.add(background);
        contentPane.add(sand);
    }
}
//draws the Bakground as grid of 10 by 10 squares
class Background extends JComponent {
    public void paintComponent(Graphics g) {

        int positionX = 0;
        int positionY = 0;

        Graphics2D g2d = (Graphics2D) g;
        g2d.setColor(Color.BLACK);


        for (int i = 0; i < getBounds().width / 10; i++) {
            g2d.drawLine(positionX, 0, positionX, getBounds().height);
            positionX += 10;
        }
        for (int i = 0; i < getBounds().height / 10; i++) {
            g2d.drawLine(0, positionY, getBounds().width, positionY);
            positionY += 10;
        }
    }
}
//draws a Sandcorn as 10 by 10 Rectangle
public class Sand extends JComponent{
    public void paintComponent(Graphics g){

        Graphics2D g2d =(Graphics2D)g;
        g2d.setColor(Color.YELLOW);
        g2d.fillRect(10, 10, 10, 10);

    }
}

I tryed to get it to work for to hours now but I couldn’t find a solution for it. I looked on Oracel and searched for some tutorials on the internet but they always worked without making any special ajustments or something like that. I would really appriciate any kind of help.