For this project you will be debugging a simple ‘games portal’ program. You can download the program as a Bluej project here. The code is complete and compiles correctly but it has a number of bugs in it that mean it doesn’t work properly. It is your job to find them.

There are two classes Player and Game. A Player has a credit balance with which they can buy games. A player can play any game they own, generating a score. The game keeps track of the best score for every player who has ever played it.

The methods on Player are:

• getName – returns the player’s name
• getCredit – returns the player’s current credit
• addCredit – adds credit to the player’s account
• buyGame – allows a player to buy a game if they have enough credit (and do not already own the game)
• ownsGame – returns whether the player owns the game

The methods on Game are:

• getName – returns the game’s name
• getCredit – returns the game’s purchase price
• play – The specified player plays the game and gets a random score. If it is better than the player’s best score so far, it is added to the high-score list
• getHighScore – get the best score for the specified player
• getBestPlayer – return the player who has the top score for this game,

There are at least seven bugs in the code. Three on Player and four on Game. You need to:

1. Read the code and try to understand what it is doing.
2. Invent test cases to check that it works the way it is supposed to.
3. When you find something wrong, try to find the nearest possible cases that work and fail.
4. Step through the different cases in the Debugger to work out what is going wrong.
5. Work out how to fix them.

Some of the bugs are trickier to find than others. Test the simpler parts of the code first, then work up to more difficult cases.

It seems that most classes spent week 5 working on the assignment, so my advice is to use this week to go back to lab 5 and continue working on it, or do revision from any of the earlier labs.

Your task today is to implement a program to represent decks and hands of playing cards.

1. Download the cards.zip file and uncompress it. It contains an incomplete BlueJ project called cards.
2. Open the project and inspect the classes:
• Card – this represents a single playing card.
• Deck – this represents a deck of cards. The constructor has been written but the methods need to be completed.
• Hand – this represents a hand of cards drawn from the deck. The fields, constructor and methods all need to be implemented.
3. Complete these classes following the comments. Do the Deck class first then the Hand class.

To complete the Deck.draw() method you will need to use the Random class in the Java API. This class provides a random number generator to pick random numbers.

To use this class you will have to import it, by putting the line:

import java.util.Random

at the top of your code.

Read the documentation to find out what constructors and methods the Random class provide.

To see what the class does, try typing the following into the Codepad:

import java.util.Random;
Random rng = new Random();
rng.nextInt(6)
rng.nextInt(6)
rng.nextInt(6)
rng.nextInt(20)
rng.nextInt(20)


Task 1: Universities

Suppose we were writing a program to administer a university. Discuss:

• What are the different levels of abstraction we might use to represent the university?
• Choose an object at the mid-level of your hierarchy. What kind of public interface might it provide? What private implementation details might it hide?

Task 2: Return to the Ticket Machine

Go back to the ticket machine project you worked on in last week’s tut.

1. Create a new class Ticket which represents a ticket.
2. Create appropriate fields. What information shoud a Ticket carry?
3. Create a constructor to initialise these fields.
4. Now modify purchaseTicket on the TicketMachine class so that it creates a new Ticket object and returns it, rather than printing it.

Let’s suppose now that a ticket has 10 charges. Each time we use it, one charge is lost.

1. Change your Ticket class to track charges. What changes do you need to make to do this?

Now let’s add a recharge method to the TicketMachine. It should take a Ticket as a parameter and reset its charges to 10 but at the cost of 1/10th of the ticketPrice for every charge added (if the user has enough balance). Implement this in stages:

1. Make the method just recharge the Ticket for free.
2. Compute how much the recharge will cost. You will need to use an accessor method on the Ticket to find out how much charge it has.
3. Add a test to see if the user has enough balance.
4. If there is not enough balance print an error message and do not recharge.
5. Subtract the charge from the balance.

Task 3: Clock

Take a look at the clock project from Chapter 3 of the textbook.

1. Investigate the NumberDisplay class first. How does it work?
2. Look at the setValue method. What does the && operator do? This is a boolean operator. Try experimenting with it in the Code Pad.
3. Look at the increment method. What does the % operator do? Try experimenting with it in the BlueJ Code Pad.
4. Now take a look at the ClockDisplay class. Try to understand how it works.
5. ClockDisplay has two constructors. How do they differ?
6. The second constructor does not call updateDisplay. Is this a bug? Why/why not?
7. Change this class to have a seconds field as well as hours and minutes.
8. Change the class to show a 12 hour clock with AM/PM.