正多角形の対角線

正多角形とその対角線を描写するプログラムをJavaで作ってみた。

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

public class Diagonal extends JFrame{
    public static void main(String[] args){
        new Diagonal();
    }

    public Diagonal(){
        setSize(500,500);
        setTitle("Diagonal");
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        MyJPanel myJPanel= new MyJPanel();
        Container c = getContentPane();
        c.add(myJPanel);
        setVisible(true);
    }

    public class MyJPanel extends JPanel{
        public static final int SIZE = 9;    //正九角形
        public MyJPanel(){
            setBackground(Color.white);
        }
        public void paintComponent(Graphics g){
            int x1,y1,x2,y2;
            double step;
            step = Math.PI*2/SIZE;
            for(double i=0; i<2 *Math.PI; i+=step){
                x1 = (int)(200*Math.cos(i));
                y1 = (int)(200*Math.sin(i));
                for(double j=i+step; j<2*Math.PI; j+=step){
                    x2 = (int)(200*Math.cos(j));
                    y2 = (int)(200*Math.sin(j));
                    g.drawLine(250-y1,250-x1,250-y2,250-x2);
                }
            }
        }
    }
}