Beginner needs help

Ok, well basically I really don't understand java, my college teacher gave me some code and I dont understand it, could someone please leave comments on the code to help me understand it a bit more?
thanks for any help given :wave:

Code:

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import javax.swing.*;
import java.awt.event.*;
import java.awt.*;

public class Pizza extends JFrame
 {
  public static void main (String [] args)
  {
  new Pizza ();
  }
JTextField name, phone, address;
JRadioButton small, medium, large, thick, thin;
JCheckBox pepperoni, mushroom, anchovies;
JButton okButton, closeButton;

 public Pizza ()
 {
 this.setTitle("PetSurvey");
 this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

 JPanel panel1 = new JPanel ();
 panel1.setLayout(new GridBagLayout());

 
 ButtonListener bl = new ButtonListener();

 addItem(panel1, new JLabel ("Name: "),
  0, 0, 1, 1, GridBagConstraints.EAST);
 addItem(panel1, new JLabel ("Phone: "),
  0, 1, 1, 1, GridBagConstraints.EAST);
 addItem(panel1, new JLabel ("Address: "),
  0, 2, 1, 1, GridBagConstraints.EAST);
 name = new JTextField (20);
 phone = new JTextField(10);
 address = new JTextField(20);

 addItem(panel1, name, 1, 0, 2, 1, GridBagConstraints.WEST);
 addItem(panel1, phone, 1, 1, 1, 1, GridBagConstraints.WEST);
 addItem(panel1, address, 1, 2, 2, 1, GridBagConstraints.WEST);

 Box sizeBox = Box.createVerticalBox();
 small = new JRadioButton("Small");
 medium = new JRadioButton("Medium");
 large = new JRadioButton("Large");
 ButtonGroup sizeGroup = new ButtonGroup();
 sizeGroup.add(small);//adding buttons to button group
 sizeGroup.add(medium);
 sizeGroup.add(large);

 sizeBox.add(small);
 sizeBox.add(medium);
 sizeBox.add(large);
 sizeBox.setBorder(BorderFactory.createTitledBorder("Size"));
 addItem(panel1, sizeBox, 0, 3, 1, 1, GridBagConstraints.NORTH);

 Box styleBox = Box.createVerticalBox ();
 thin = new JRadioButton("Thin");
 thick = new JRadioButton("Thick");
 ButtonGroup styleGroup = new ButtonGroup();
 styleGroup.add(thin);
 styleGroup.add(thick);
 styleBox.add(thin);
 styleBox.add(thick);
 styleBox.setBorder(BorderFactory.createTitledBorder ("Style"));
 addItem(panel1, styleBox, 1, 3, 1, 1, GridBagConstraints.NORTH);

 Box topBox = Box.createVerticalBox();
 pepperoni = new JCheckBox("Pepperoni");
 mushroom = new JCheckBox("Mushroon");
 anchovies = new JCheckBox("Anchovies");
 topBox.add(pepperoni);
 topBox.add(mushroom);
 topBox.add(anchovies);
 topBox.setBorder(BorderFactory.createTitledBorder("Toppings"));
 addItem(panel1, topBox, 2, 3, 1, 1,  GridBagConstraints.NORTH);
 Box buttonBox = Box.createHorizontalBox();
 okButton = new JButton("OK");
 okButton.addActionListener(bl);

 closeButton = new JButton ("Close");
 closeButton.addActionListener(bl);

 buttonBox.add(okButton);
 buttonBox.add(Box.createHorizontalStrut (20));
 buttonBox.add(closeButton);
 addItem(panel1, buttonBox, 2, 4, 1, 1, GridBagConstraints.NORTH);
 this.add(panel1);
  this.pack ();
 this.setVisible(true);
 }
private void addItem(JPanel p, JComponent c, int x, int y, int width, int height, int align)
 {
 GridBagConstraints gc = new GridBagConstraints ();
 gc.gridx = x;
 gc.gridy = y;
 gc.gridwidth = width;
 gc.gridheight = height;
 gc.weightx  = 100.0;
 gc.weighty = 100.0;
 gc.insets = new Insets (5, 5, 5, 5);
 gc.anchor = align;
 gc.fill = GridBagConstraints.NONE;
 p.add(c, gc);
 }
 private class ButtonListener implements ActionListener

 {
  public void actionPerformed(ActionEvent e)
  {
  if (e.getSource() == okButton)
  {
    String tops = "" ;
  if (pepperoni.isSelected()) tops +="Pepperoni\n";
  if (mushroom.isSelected()) tops += "Mushroon \n";
  if (anchovies.isSelected()) tops += "Anchovies\n";

 
    String base = " your base type is ";
  if (thick.isSelected()) base += "Thick";
  if(thin.isSelected()) base += "Thin";


    String msg = "You ordered a ";
  if(small.isSelected()) msg += "small pizza with ";
  if(medium.isSelected()) msg += "medium pizza with ";
  if (large.isSelected ()) msg += "large pizza with ";

  //String name = name.getText;
 
  if(tops.equals(""))
 
  msg += "you have selected no toppings";
  else

  msg += "the following toppings:\n "+ tops + base;


 JOptionPane.showMessageDialog(okButton, msg, "Your Order!", JOptionPane.INFORMATION_MESSAGE);

 pepperoni.setSelected(false);
 mushroom.setSelected(false);
 anchovies.setSelected(false);
 thick.setSelected(false);
 thin.setSelected(true);
 small.setSelected(true);
  }

  if (e.getSource() == closeButton)
  {
    System.exit(0);
  }
  }
}
 
}

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