The following exercises are taken from chapter 8 of the textbook.

Exercise 8.4 Open the project dome-v2. This project contains a version of the DoME application rewritten to use inheritance, as described above. Note that the class diagram displays the inheritance relationship. Open the source code of the DVD class and remove the ‘extends Item‘ phrase. Close the editor. What changes do you observe in the class diagram? Add the ‘extends Item‘ phrase again.

Exercise 8.5 Create a CD object. Call some of its methods. Can you call the inherited methods (for example, setComment)? What do you observe about the inherited methods?

Exercise 8.6 In order to illustrate that a subclass can access non-private elements of the superclass without any special syntax, try the following slightly artificial modification to the CD and Item classes. Create a method called printShortDetails in the CD class. Its task is to print just the artist and the title of a CD on a line by itself. However, because the titIe field is private in the Item class, it will be necessary to add a public getTitIe method to Item. Call this method from printShortDetails to access the title for printing. Remember that no special syntax is required when a subclass calls a superclass method. Try out your solution by creating a CD object. Implement a similar method in the DVD class to print just the director and title.

Exercise 8.8 Open the dome-v2 project. Add a class for games and a subclass for video games to the project. Create some video game objects and test that all methods work as expected.

Exercise 8.12 Assume we have four classes: Person, Teacher, Student and PhDStudent. Teacher and Student are both subclasses of Person. PhDStudent is a subclass of Student.

a. Which of the following assignments are legal, and why or why not?

Person p1 = new Student();
Person p2 = new PhDStudent();
PhDStudent phd1 = new Student();
Teacher t1 = new Person();
Student s1 = new PhDStudent();


b. Suppose that we have the following legal declarations and assignments

Person p1 = new Person();
Person p2= new PerSon ();
PhDStudent phd1 = new PhDStudent();
Teacher t1 = new Teacher () ;
Student s1 = new Student();


Based on those just mentioned, which of the following assignments are legal and or why not?

s1 = p1;
s1 = p2;
p1 = s1;
t1 = st;
s1 = phd1;
phd1 = s1;


Exercise 8.13 Test your answers to the previous question by creating bare-bones versions of the classes mentioned in that exercise and trying it out in BlueJ

JUnit Testing

For the exercises this week, download the diary-testing-junit-v2 project. These examples and exercises are based on chapter 6 of the textbook.

1. Using the diary-testing-junit-v2 project, create a method in DayTest to check that findSpace returns the value of 10 for a one-hour appointment if a day already has a single one-hour appointment at 9 a.m. You must first create the 9 a.m. appointment, then the 10 a.m appointment. Specify assertions for the results of both calls.
2. Create a test to check that findSpace returns a value of -1 if an attempt is made to find an appointment In a day that is already full.
3. Create a test class that has Appointment as its reference class. Record separate test methods within It that check that the description and duration flelds of an Appointment object are initialised correctly following its creation.
4. Create the following negative test in the DayTest class. Create a Day object, a one-hour Appointment object and a two-hour Appointment object. Make the one-hour appointment at 10 a.m. and then try to make the two-hour appointment at 9 a.m. Since this call to makeAppointment should fail, the value to put into the assertion is false. Now run the test. What is shown in the test results window?

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.