// method for drawing on a JPanel
public void paintComponent(Graphics g) {
    super.paintComponent(g);   // call constructor of JPanel   
    g.drawString("This is my custom Panel!",10,20); // draw text
    g.setColor(Color.red);   // set the drawing color to red
    g.fillRect(20,40,50,100);  // draw a filled red rectangle
}