Sierpinski's fractal triangles - Java Object Oriented Design

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Description

Sierpinski's fractal triangles

Demo Code

import java.awt.Graphics;
import java.awt.Point;

import javax.swing.JFrame;

public class Main extends JFrame {
  public static final int WINDOW_SIZE = 512;
  public static final int THRESHOLD = 10; // stopping criterion for recursion
  public static int P1_x, P1_y, P2_x, P2_y, P3_x, P3_y;

  public Main() {
    super("Sierpinski");

    setSize(WINDOW_SIZE, WINDOW_SIZE);//from   w w  w  .  ja  v  a 2  s  . c om

    // A simple triangle
    P1_x = (int) getSize().getWidth() / 2;
    ;
    P1_y = 40;
    P2_x = 20;
    P2_y = (int) getSize().getHeight() - 20;
    P3_x = (int) getSize().getWidth() - 20;
    P3_y = (int) getSize().getHeight() - 20;

    setVisible(true);

    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  }

  // Compute the midpoint
  public Point getMiddle(Point p1, Point p2) {
    return new Point((int) (p1.getX() + p2.getX()) / 2, (int) (p1.getY() + p2.getY()) / 2);
  }

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

    draw(new Point(P1_x, P1_y), new Point(P2_x, P2_y), new Point(P3_x, P3_y));
  }

  public void draw(Point p1, Point p2, Point p3) {
    // termination condition
    if (p1.distance(p2) < THRESHOLD && p1.distance(p3) < THRESHOLD && p2.distance(p3) < THRESHOLD)
      return; // stop recursion
    // draw the current triangle
    Graphics g = getGraphics();
    g.drawLine((int) p1.getX(), (int) p1.getY(), (int) p2.getX(), (int) p2.getY());
    g.drawLine((int) p2.getX(), (int) p2.getY(), (int) p3.getX(), (int) p3.getY());
    g.drawLine((int) p3.getX(), (int) p3.getY(), (int) p1.getX(), (int) p1.getY());
    // recursively draw the 3 smaller corner triangles
    Point m12 = getMiddle(p1, p2);
    Point m23 = getMiddle(p2, p3);
    Point m31 = getMiddle(p3, p1);
    // Recursive calls
    draw(p1, m12, m31);

    draw(p2, m23, m12);

    draw(p3, m31, m23);
  }

  public static void main(String[] args) {
    new Main();
  }
}

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