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

 public class Poly extends JPanel implements ActionListener {
   private int n, r;
   private double vinkel;
   private int[] x, y;
   private double dv = 5*2*Math.PI/360;  // 5 grader
   private double vrid = 0;
   private Timer tim = new Timer(100, this);

   public Poly(int antal, int radie) { // konstruktor
     n = antal; r = radie;
     x = new int[n];
     y = new int[n];
     vinkel = 2*Math.PI/n;
   }

   public void start() {
     tim.start();        // starta timern
   }

   public void stop() {
     tim.stop();        // stoppa timern
   } 
   
   public void actionPerformed(ActionEvent e) {
     // hit kommer man var 100:e ms
     vrid = vrid + dv;
     if (vrid>2*Math.PI)
       vrid -= 2*Math.PI; 
     repaint();
   }

   @Override
   public void paintComponent(Graphics g) {
     super.paintComponent(g);  // suddar bakgrunden
     int x0 = getSize().width/2;
     int y0 = getSize().height/2;
     // räkna ut nya hörnpunkter
     for (int i=0; i<n; i++) {
       double v = i*vinkel - vrid; 
       x[i] = x0 + (int)Math.round(r * Math.cos(v));
       y[i] = y0 - (int)Math.round(r * Math.sin(v));
     }
     // rita ny bild
     g.fillPolygon(x, y, n);
   }
 }