Need help to create the Sierpiński Carpet using recursion

[Krupa Patel]

I am trying to create the Sierpinski Carpet using recursion. I divided the square into nine equal squares in the three rows and three columns.
And the center sub-square is removed.
I do not know how to repeat that process for the eight remaining sub-squares which surround the center square that was “removed.”
This is my code:

import javax.swing.*;
import java.awt.*;
public class FractalApp extends JFrame{
	FractalPanel _fp;
	public FractalApp(String title){
		super(title);
		this.setSize(729,729);
		this.setDefaultCloseOperation(javax.swing.JFrame.EXIT_ON_CLOSE);
		_fp = new FractalPanel();
		_fp.setPreferredSize(new Dimension(729,729));
		this.add(_fp);
		this.pack();
		this.setVisible(true);
	}
	public static void main(String[] args){
		FractalApp app = new FractalApp("Sierpinski Carpet");
	}
}

import javax.swing.*;
import java.awt.*;
import java.awt.geom.*;
class FractalPanel extends JPanel{
	public FractalPanel(){
		super();
		this.setBackground(java.awt.Color.BLACK);
	}
    public void paintComponent(Graphics g)
    {   super.paintComponent(g);
        Graphics2D pen = (Graphics2D) g;
        pen.setColor(java.awt.Color.WHITE);
	  paintFractal(pen, 0, 0, this.getSize().height);
    }
    public void paintFractal(Graphics2D pen, int x, int y, int len){
        Graphics2D g2 = (Graphics2D)pen;
        int side = len/3;
        Rectangle2D rect = new Rectangle2D.Double(x+side,y+side,side,side);
        g2.fill(rect); 
     }
}	

Please help me.

[Campbell Ritchie]

Don’t know. But I do know you can’t work it out in code. You have to work it out on paper. What is the algorithm?