java使用Turtle的方法编写一个递归来绘制一个反向的科赫雪花（一个雪花由三份科赫曲线组成，在正三角形的边上尖端向内构建）

好的，下面是Java使用Turtle绘制反向科赫雪花的递归代码：

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Polygon;
import java.awt.Rectangle;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class KochSnowflake extends JPanel {
  private static final long serialVersionUID = 1L;
  private int level = 0;

  public KochSnowflake(int level) {
    this.level = level;
  }

  @Override
  protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    // 背景颜色
    g.setColor(Color.WHITE);
    Rectangle r = g.getClipBounds();
    g.fillRect(0, 0, r.width, r.height);
    // 设置画笔颜色和粗细
    g.setColor(Color.BLACK);
    g.setLineWidth(1);
    // 顶点坐标
    int x1 = 0, y1 = (int) (Math.sqrt(3) / 2 * r.height);
    int x2 = r.width / 2, y2 = 0;
    int x3 = r.width, y3 = (int) (Math.sqrt(3) / 2 * r.height);
    // 构建三角形
    Polygon p = new Polygon(new int[] {x1, x2, x3}, new int[] {y1, y2, y3}, 3);
    g.drawPolygon(p);
    // 初始的三分科赫曲线
    drawKochLine(p.xpoints[0], p.ypoints[0], p.xpoints[1], p.ypoints[1], level, g);
    drawKochLine(p.xpoints[1], p.ypoints[1], p.xpoints[2], p.ypoints[2], level, g);
    drawKochLine(p.xpoints[2], p.ypoints[2], p.xpoints[0], p.ypoints[0], level, g);
  }

  /**
   * 绘制科赫曲线
   *
   * @param x1     起点横坐标
   * @param y1     起点纵坐标
   * @param x2     终点横坐标
   * @param y2     终点纵坐标
   * @param level  当前绘制的递归层级
   * @param g      绘制所使用的画笔
   */
  private void drawKochLine(int x1, int y1, int x2, int y2, int level, Graphics g) {
    if (level == 0) {
      // 到达递归终点
      g.drawLine(x1, y1, x2, y2);
      return;
    }
    int deltaX = x2 - x1;
    int deltaY = y2 - y1;
    // 计算三等分点坐标
    int x1_3 = x1 + deltaX / 3, y1_3 = y1 + deltaY / 3;
    int x2_3 = x1 + deltaX * 2 / 3, y2_3 = y1 + deltaY * 2 / 3;
    int x_control = (int) ((x1 + x2) / 2.0 - Math.sqrt(3) * (y2 - y1) / 6);
    int y_control = (int) ((y1 + y2) / 2.0 - Math.sqrt(3) * (x2 - x1) / 6);
    // 递归绘制
    drawKochLine(x1, y1, x1_3, y1_3, level - 1, g);
    drawKochLine(x1_3, y1_3, x_control, y_control, level - 1, g);
    drawKochLine(x_control, y_control, x2_3, y2_3, level - 1, g);
    drawKochLine(x2_3, y2_3, x2, y2, level - 1, g);
  }

  public static void main(String[] args) {
    JFrame frame = new JFrame("Koch Snowflake");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    KochSnowflake panel = new KochSnowflake(5); // 设置递归层数
    frame.getContentPane().add(panel);
    frame.setSize(800, 800);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
  }
}