如何在JFrame中实现希尔伯特曲线

import javax.swing.JFrame;
import java.awt.Graphics;
import java.awt.Graphics2D;

public class HilbertCurveFrame extends JFrame {
    private int level;

    public HilbertCurveFrame(int level) {
        this.level = level;
        setSize(800, 800);
        setTitle("Hilbert Curve");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    @Override
    public void paint(Graphics g) {
        super.paint(g);
        Graphics2D g2d = (Graphics2D) g;
        drawHilbertCurve(g2d, level, 100, 100, 600, 600, 0);
    }

    private void drawHilbertCurve(Graphics2D g2d, int level, int x1, int y1, int x2, int y2, int direction) {
        if (level == 0) {
            g2d.drawLine(x1, y1, x2, y2);
            return;
        }

        int deltaX = (x2 - x1) / 2;
        int deltaY = (y2 - y1) / 2;

        if (direction == 0) {
            drawHilbertCurve(g2d, level - 1, x1, y1, x1 + deltaX, y1 + deltaY, 0);
            drawHilbertCurve(g2d, level - 1, x1 + deltaX, y1, x1 + deltaX, y1 + deltaY, 1);
            drawHilbertCurve(g2d, level - 1, x1 + deltaX, y1 + deltaY, x1, y1 + deltaY, 0);
            drawHilbertCurve(g2d, level - 1, x1, y1 + deltaY, x1, y1, 3);
        } else if (direction == 1) {
            drawHilbertCurve(g2d, level - 1, x1, y1, x1 + deltaX, y1 + deltaY, 0);
            drawHilbertCurve(g2d, level - 1, x1 + deltaX, y1, x1 + deltaX, y1 + deltaY, 1);
            drawHilbertCurve(g2d, level - 1, x1 + deltaX, y1 + deltaY, x1, y1 + deltaY, 1);
            drawHilbertCurve(g2d, level - 1, x1, y1 + deltaY, x1, y1, 2);
        } else if (direction == 2) {
            drawHilbertCurve(g2d, level - 1, x1, y1, x1, y1 + deltaY, 3);
            drawHilbertCurve(g2d, level - 1, x1, y1 + deltaY, x1 + deltaX, y1 + deltaY, 2);
            drawHilbertCurve(g2d, level - 1, x1 + deltaX, y1 + deltaY, x1 + deltaX, y1, 2);
            drawHilbertCurve(g2d, level - 1, x1 + deltaX, y1, x1, y1, 1);
        } else if (direction == 3) {
            drawHilbertCurve(g2d, level - 1, x1, y1, x1, y1 + deltaY, 3);
            drawHilbertCurve(g2d, level - 1, x1, y1 + deltaY, x1 + deltaX, y1 + deltaY, 2);
            drawHilbertCurve(g2d, level - 1, x1 + deltaX, y1 + deltaY, x1 + deltaX, y1, 0);
            drawHilbertCurve(g2d, level - 1, x1 + deltaX, y1, x1, y1, 3);
        }
    }

    public static void main(String[] args) {
        HilbertCurveFrame frame = new HilbertCurveFrame(5);
        frame.setVisible(true);
    }
}