Create A Grocery Store Calculator In Netbeans GUI

I need to create a grocery store calculator in Netbeans GUI. It should function as follows:

1. Click "Checkout"
2. Enter item price screen pops up.
3. Input item price, and store price in Item price, subtotal and display in those text fields. Also store item number in number of items and display in text field, all after you click "Ok".
4. Enter item price screen should automatically pop back up. (Loop)
5. Once you are finished with all items, when you click "Ok" or "Cancel" with nothing in the text field. It should calculate sales tax/ total sale and display both.
6. Rest button should reset to the beginning and Exit button should exit program.

GUI 1.jpgGUI 2.jpg

The good news is my program works right now. Although I do not believe I am using the setter/getter methods correctly. More importantly I do not fully understand them. I left out the Generated code due to the length.

import java.text.NumberFormat;
import javax.swing.JOptionPane;
public class Assignment4 extends javax.swing.JFrame {
NumberFormat nF = NumberFormat.getCurrencyInstance();
private Object JoptionPane;
private double purchase; //private instance variables
private int numItems; //private instance variables

[code]....