Assignment 4 – Packages

COMP 2150 Assignment 4 –
Packages
 (Java): Point of Sale: Part 3
For this question you will add additional features to your Point of Sale server from the previous
assignment. You may use your own solution, or the posted model solution. The new features will be:
1. A client. Rather than developing this yourself, though, you will be using a pre-compiled Java
class given to you, and connecting it to your server.
2. Packages. The client and server will be organized into separate packages, along with a main
program that will launch both.
3. A singleton. This will ensure that there is only ever a single instance of your server, no matter
how many clients are connected to it.
4. Order cancellation. A transaction (any of the three types) can be cancelled.
Your client will be interactive, implemented using the given InteractiveClient class. This class has only
one useful public method:
To use this class, call the nextCommand() method repeatedly. It will return strings that you can then
translate into commands that you can pass to your server. Use features of your server in your responses
to commands; for example, print the total count and quantity of items and cost of a transaction as you
add items to it. Error messages from your server can also be printed.
To organize your system, divide it into three packages:
 comp2150.pos.client contains the client
 comp2150.pos.server will contain your server implementation
 comp2150.pos.main contains the main program that starts up the server and the client
public static String comp2150.pos.client.nextCommand()
 Get the next command entered, if any. Returns null if the user chooses to quit.
Method Summery
Since there will only ever be one server in your system, you can enforce this uniqueness using the
Singleton design pattern. Implement the singleton as a class called A4Server in the server
implementation package. To enforce the information hiding for your server implementation, your server
class must be private to the comp2150.pos.server package (that is, it should have default or package
visibility, and not public).
Any transaction can be cancelled using the new server interface method cancelTransaction(). Cancelling
a purchase will return all the items in the purchase to the inventory; that is, the in-stock quantity will be
increased by the amounts from the transaction. Cancelling a backorder will remove backordered items
from the inventory backorder quantity and return any purchased items to inventory. Cancelling a return
will have no effect on inventory. Cancelled transactions are marked as "cancelled" rather than
completed.
There is one other change required by cancellations. Transactions can only be cancelled from the client
that created the transaction. Therefore, transactions must keep track of which client created them using
a client ID. This ID has been added to createTransaction(), and is also used in cancelTransaction().
These changes require an updated server interface A4POSServer.java. Use the inventory file from the
previous assignment. With your assignment submission, include an OUTPUT.txt file with your
assignment submission that shows the output of running your program (copy and paste). Ensure that it
includes:
 more than one client;
 purchases, backorders, and returns;
 cancellations of all three types of orders;
 searches (with multiple matches) and summaries; and
 both successful and failed actions (e.g. cancelling from the wrong client).