Java AWT Graphics fill arc as rainbow

// Drawing a rainbow using arcs and an array of colors.
import java.awt.Color;
import java.awt.Graphics;

import javax.swing.JFrame;
import javax.swing.JPanel;

class DrawRainbow extends JPanel {
   // define indigo and violet
   private final static Color VIOLET = new Color(128, 0, 128);
   private final static Color INDIGO = new Color(75, 0, 130);

   // colors to use in the rainbow, starting from the innermost
   // The two white entries result in an empty arc in the center
   private Color[] colors = { Color.WHITE, Color.WHITE, VIOLET, INDIGO, Color.BLUE, Color.GREEN, Color.YELLOW,
         Color.ORANGE, Color.RED };

   // constructor
   public DrawRainbow() {
      setBackground(Color.WHITE); // set the background to white
   } // end DrawRainbow constructor

   // draws a rainbow using concentric arcs
   public void paintComponent(Graphics g) {
      super.paintComponent(g);

      int radius = 20; // radius of an arc

      // draw the rainbow near the bottom-center
      int centerX = getWidth() / 2;
      int centerY = getHeight() - 10;

      // draws filled arcs starting with the outermost
      for (int counter = colors.length; counter > 0; counter--) {
         // set the color for the current arc
         g.setColor(colors[counter - 1]);

         // fill the arc from 0 to 180 degrees
         g.fillArc(centerX - counter * radius, centerY - counter * radius, counter * radius * 2, counter * radius * 2,
               0, 180);/*w w w .  j  a  v  a 2 s .c  o m*/
      }
   }
}

public class Main {
   public static void main(String[] args) {
      DrawRainbow panel = new DrawRainbow();
      JFrame application = new JFrame();

      application.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      application.add(panel);
      application.setSize(400, 250);
      application.setVisible(true);
   }
}