Java Swing : Menu Program

import javax.swing.*;
/*
  <APPLET
  CODE="Pickupmenu"
  WIDTH=400
  HEIGHT=100>
  </APPLET>
*/
public class Pickupmenu extends JApplet {

  public void init() {
    try {
      SwingUtilities.invokeAndWait(
        new Runnable() {
          public void run() {
            makeGUI();
          }
        }
      );
    } catch (Exception exc) {
      System.out.println("Sorry, your order cannot be processed " +
                         exc);
    }
  }    

  private void makeGUI() {

    JTabbedPane jtp = new JTabbedPane();
    jtp.addTab("Pizza", new Piz());
    jtp.addTab("Toppings", new Top());
    jtp.addTab("Beverage", new Bevr());
jtp.addTab("Add-ons", new AdOn());
  add(jtp);
  }
}

class Piz extends JPanel {

  public Piz() {

    JRadioButton a1 = new JRadioButton("Classic");
    add(a1);
    JRadioButton a2 = new JRadioButton("Hand-tossed");
    add(a2);
    JRadioButton a3 = new JRadioButton("Special Crust");
    add(a3);
  }
}

class Top extends JPanel {

  public Top() {

    JCheckBox b1 = new JCheckBox("Onion");
    add(b1);
    JCheckBox b2 = new JCheckBox("Capsicum");
    add(b2);
    JCheckBox b3 = new JCheckBox("Tomato");
    add(b3);
JCheckBox b4 = new JCheckBox("Plain Cheese");
    add(b3);

  }
}

class Bevr extends JPanel {

  public Bevr() {
   
    JComboBox c = new JComboBox();
    c.addItem("Coke");
    c.addItem("Pepsi");
    c.addItem("7'up");
    c.addItem("Sprite");
    add(c);
  }
}

class AdOn extends JPanel {

  public AdOn() {
   
    JButton d1 = new JButton("Garlic Bread");
add(d1);
    JButton d2 = new JButton("Chocolate Cake");
add(d2);
    JButton d3 = new JButton("Salads");
add(d3);
  }
}