public class PostalZipCode
{
    private String barCode;
 
    public PostalZipCode(String zipCode)
    {
        determinateBarCode(zipCode);
    }
 
    private void determinateBarCode(String zipCode)
    {
        //do what ever calculation you need to generate barCode
        setBarCode(GENERATED_STRING_FOR_BARCODE_HERE);
    }
 
    private void setBarCode(String str)
    {
        barCode = str;
    }
 
    public void getBarCode()
    {
        return barCode;
    }
}

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

public class PostOffice extends JFrame implements ActionListener
{
    //This appears on the screen as a clickable button
    private JButton zipCodeButton;
    //This appears as two text fields where you can type
    private JTextField zipCodeField, barCodeField;
    //This appears as text, a label next to the zip code field
    private JLabel zipCodeLabel;
    
    //This is the variable your professor has created to get input
    //from the GUI. 
    private PostalZipCode myZip;
    
    public static void main ()
    {
        //All of this code creates the GUI and shows it to you
        //You shouldn't be concerned with it, and you do not
        //need to alter it or add to it in any way. 
        PostOffice myApplication = new PostOffice();
        myApplication.setSize(400,140);
        myApplication.setTitle("Zip Code");
        myApplication.createGUI();
        myApplication.setVisible(true);
    }
    
    //Again, more code to create the GUI. You do not need to
    //change any of this code either
    private void createGUI()
    {
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        Container window = getContentPane();
        window.setLayout(new FlowLayout());
        
        zipCodeLabel = new JLabel(" Zip Code ");
        window.add(zipCodeLabel);
        zipCodeField = new JTextField(5);
        window.add(zipCodeField);
        
        barCodeField = new JTextField(20);
        barCodeField.setHorizontalAlignment(JTextField.CENTER);
        barCodeField.setFont(new Font("Sans erif", Font.BOLD, 20));

        window.add(barCodeField);
        
        zipCodeButton = new JButton("Display Postal Bar Code");
        zipCodeButton.addActionListener(this);
        window.add(zipCodeButton);
    }
    
  //The code that you are primarily concerned with is in here.
    public void actionPerformed (ActionEvent e) 
    {
        //Your professor reads in the zip code
        String userInput = zipCodeField.getText();
        //Here, your professor takes a zip code, "userInput", and 
        //calls a constructor that converts it to a PostalZipCode.
        //You need to write that constructor. Doing so involves creating a new class called PostalZipCode, writing a constructor called PostalZipCode that converts a Zip code to a PostalZipCode.
        myZip = new PostalZipCode(userInput);
        //In your PostalZipCode class, you need a method call getBarCode() that returns a String. The String should be the bar code. 
        barCodeField.setText(myZip.getBarCode());
    }
}

public class PostalZipCode{
String thisZipCode = "";
String postalZipCode = "";
String barCode = "";

public PostalZipCode(String zipCode){
thisZipCode = zipCode;
postalZipCode = convertZipcodeToPostal(zipCode);
setBarCode();
}

public String convertZipcodeToPostal(String aZip){
String postalCode = "";
//Do whatever you need to to aZip to convert it to a postalZipCode.
return postalCode;
}

public void setBarCode(){
//write code that uses the zipCode to set the bar code
}

public String getBarCode(){
 return barCode;
}

}