Java Code CashTill

Java Code CashTill

I have the following problem. we have a CashTill program that uses GUI...
it has 3 buttons:
Perform a Sale
List of Inventory and
Quit the program
When i click the "Perform a Sale" button, a new set of commands is
presented in the JFrame that ask the user to input a 5 digit product id to
identify what is being ordered. The program will not stop asking for 5
digit product ID's until the number 0 is entered. Then for every product
ID, the given product will lose some of its stock from the inventory
depending on the users input.
How can I use a looping statement or how can I continue asking for 5 digit
product ID's every time a user enters a number that is not equal to 0.
Additionally, I need to return the value of the number of items in stock
for the list of inventory.