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

class Mystery extends JPanel
              implements Runnable {
  static final double p = 0.8660254; // sqrt(3) / 2
  int x = 50, y = 0,  z = 0,
      dx = 0, dy = 1, dz = 0;
  Thread thread = null;

  public Mystery() {
    setPreferredSize(new Dimension(220, 220));
    startThread();
  }

  public void startThread() {
    if (thread == null) {
      thread = new Thread(this);
      thread.start();
    }
  }

  public void stopThread() {
    thread = null;
  }

  @Override
  public void run() {
    Thread me = Thread.currentThread();
    while (thread == me) {
      for (int i = 0; i < 50; i++) {
        x += dx;   y += dy;   z += dz;
        repaint();
        try {
          Thread.sleep(40);
        } catch (InterruptedException e) {
        }
      }
      int tmp = dz; dz = -dx; dx = -dy; dy = -tmp;
    }
  }

  @Override
  public void paintComponent(Graphics g) {
    super.paintComponent(g);
    g.setColor(new Color((int)(x * 255.0 / 50.0),
                         (int)(y * 255.0 / 50.0),
                         (int)(z * 255.0 / 50.0)));
    double x0 = 0.0 * x + p   * y - p   * z,
           y0 = 1.0 * x - 0.5 * y - 0.5 * z;
    g.fillOval(100 + (int)(x0 * 2),
               100 + (int)(y0 * 2), 20, 20);
  }
}

void main() {
  SwingUtilities.invokeLater(() -> {
    JFrame frame = new JFrame("Mystery!");
    frame.add(new Mystery());
    frame.pack();
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  });
}