Java AWT Graphics fill whole window

import java.awt.Graphics;

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

class DrawPanel extends JPanel {
   public void paintComponent(Graphics g) {
      super.paintComponent(g);

      int width = getWidth();
      int height = getHeight();


      g.fillRect(0, 0, width, height);/*from  ww w  .  j  a v  a  2  s .co m*/

   }
}

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

      JFrame application = new JFrame();

      application.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

      application.add(panel);
      application.setSize(250, 250);
      application.setVisible(true);
   }
}