Java draw h tree fractal

HTreeTextField.java

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class HTreeTextField extends JFrame {
    
    private JTextField tf = new JTextField("0", 5);
    private HTree htree = new HTree();
    
    public HTreeTextField() {
        htree.setSize(600, 500);
        htree.setLocation(150, 150);
        htree.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
        JPanel panel = new JPanel();
        panel.add(new JLabel("Enter an order: "));
        panel.add(tf);
        
        add(panel);
        
        tf.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                int order = Integer.parseInt(tf.getText());
                htree.setOrder(order);
                htree.setVisible(true);
            }
        });
    }
    
    public static void main(String[] args) {
        JFrame f = new HTreeTextField();
        f.setSize(150, 150);
        f.setLocationRelativeTo(null);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setVisible(true);
    }
}

class HTree extends JFrame {

    private int order = 0;

    public void setOrder(int order) {
        this.order = order;
        repaint();
    }

    public void paint(Graphics g) {
        super.paint(g);

        Point p1 = new Point(200, 160);
        Point p2 = new Point(200, 360);
        Point p3 = new Point(400, 160);
        Point p4 = new Point(400, 360);

        g.setColor(Color.red);
        
        displayHTree(g, order, 200, p1, p2, p3, p4);
    }

    private void displayHTree(Graphics g, int order, int size,
            Point p1, Point p2, Point p3, Point p4) {

        g.drawLine(p1.x, p1.y, p2.x, p2.y);
        g.drawLine(p3.x, p3.y, p4.x, p4.y);
        g.drawLine(p1.x, p1.y + size / 2, p3.x, p3.y + size / 2);

        if (order > 0) {
            Point[] p1Points = splitLine(p1, size);
            Point[] p2Points = splitLine(p2, size);
            Point[] p3Points = splitLine(p3, size);
            Point[] p4Points = splitLine(p4, size);

            displayHTree(g, order - 1, size / 2,
                    p1Points[0], p1Points[1], p1Points[2], p1Points[3]);

            displayHTree(g, order - 1, size / 2,
                    p2Points[0], p2Points[1], p2Points[2], p2Points[3]);

            displayHTree(g, order - 1, size / 2,
                    p3Points[0], p3Points[1], p3Points[2], p3Points[3]);

            displayHTree(g, order - 1, size / 2,
                    p4Points[0], p4Points[1], p4Points[2], p4Points[3]);
        }
    }

    private Point[] splitLine(Point p, int size) {
        Point[] points = new Point[4];
        points[0] = new Point(p.x - size / 4, p.y - size / 4);
        points[1] = new Point(p.x - size / 4, p.y + size / 4);
        points[2] = new Point(p.x + size / 4, p.y - size / 4);
        points[3] = new Point(p.x + size / 4, p.y + size / 4);

        return points;
    }
}