Draw Rectangles in Java Swing Example

import javax.swing.*;


import java.awt.*;


public class JRectanglesJavaExample extends JFrame


   {


       Container cntnr = getContentPane();


       public JRectanglesJavaExample()


          {


              cntnr.setBackground(Color.GREEN);


              cntnr.setLayout(new FlowLayout());


          }


              public void paint(Graphics gr)


                {


                           super.paint(gr);


                           gr.setColor(Color.YELLOW);


                           gr.fillRect(50, 50, 130, 130);


                           gr.clearRect(60, 70, 60, 60);


               }


                          public static void main(String[] ag)


                           {


                                JRectanglesJavaExample frm = new JRectanglesJavaExample();


                                frm.setSize(230,230);


                                frm.setVisible(true);


                           }


   }