Marking Guide Mid Semester S2 2010

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COSC 1288/1290/1295
Java for (C) Programmers
Mid Semester Test, Semester 2 2010

Instructions
1. This test is worth 5% of your final mark. However, the most valuable aspect is measuring
2.
3.
4.
5.

your own progress. This test is NOT a hurdle for the course.
Do the test on your own. You may refer to the course notes if you want but you should
not need to and doing so will probably slow you down.
This test is to be done during Week 8 lecture, except in exceptional circumstances. The
allocated time for the test is 40 minutes.
You must attend your Week 8 tutorial for marking and to receive feedback.
Write all your answers on the test paper and hand that in.

Name:

Student number:

1

Part A: Short Answers: 8 marks (2 marks each)
A.1

Any exception that can be thrown in a method X and is NOT caught inside X
(Just circle your answer)
A. must be ignored
B. must be declared as part of the signature of the main() method
C. must never occur
D. must be declared as part of the method X’s signature
E. none of the above.
D – 2 marks; anything else is 0

A.2 Which one of the following statements about Interface and Abstract Class is FALSE?
A. All methods in an abstract class must be abstract.
B. An interface cannot implement any methods, but an abstract class can.
C. An interface cannot have instance variables, but an abstract class can.
D. A Java class can extend only one direct superclass.
E. A Java class can implement more than one interface.
A – 2marks; anything else is 0

A.3 What do each of the two ―super‖ refer to in the following code snippet:
public class SportsCar extends Car
{
...
public SportsCar() {
super();
}
...
public double accelerate() {
return super.accelerate() * 1.5;
}
}
A:

constructor in Car / superclass

B:

superclass / method in superclass

// A

// B

1 mark each

2

A.4 Assume that Circle is a subclass of Shape; consider the following variable declarations.
Shape shape1 = new Shape();
Shape shape2 = new Circle();
Circle circle2;
Which of the assignment statement(s) below will NOT cause any problem? CIRCLE THE LETTER(S).
A. circle2 = (Circle) shape1;
B. circle2 = (Circle) shape2;
C. circle2 = shape1;
D. circle2 = shape2;
B – 2 marks
A, B, D OR B only OR D only – 1 mark
0 for anything else

3

PART B: Simple Programming Exercise: 8 marks
Question B.1
(8 marks)
Complete the following program that reads in an unknown number of integers from standard
input and returns the smallest integer entered.
You must allow for any number of input integers—the input finishes by the user typing
an empty line.
You may assume valid input—i.e. you don’t have to do error-checking on the input.
Use Scanner to read the input.
public class Min {
public int min() {
Scanner input = new Scanner( ....
...

Scanner input = new Scanner(System.in);
int i;
int min = input.nextInt(); // should have “if hasNextInt()” but ok not to
while (input.hasNextInt()) {
i = input.nextInt();
if (i < min)
min = i;
}
return min;
1 mark for each line above
-1 mark if min is given a default starting value (e.g. 0)
(students will be given Scanner API so they should use it correctly)

4

PART C: Basic Object Oriented Programming: 14 marks
For this question, you need to write Java classes for a Movie Rental system.
You need a Customer class but you do not have to write this class: assume this class stores a
name as a String and contains the method: String getName().
(a) Write the Movie class.
(10 marks)
A Movie has a title (String) and a year (int); the year is optional. Each Movie object also keeps
track of whether it is borrowed---it is available if it is not already borrowed. If a Movie is
borrowed, then it stores the Customer object who has borrowed it.
Write the Movie class:
Make sure you include all the right fields. You do NOT have to write accessors for them.
You need two constructor to create a movie object---remember that every movie must have a
title when it is constructed; a year is optional: a Movie can be constructed with a year, but it
doesn’t have to be.
Write the method isAvailable(), that returns a Boolean.
Create methods rent(Customer c) and return() -- the first method rents the movie to the
Customer c and the second one ―returns‖ a movie that is out on rent (i.e. makes it available
again).
o If a movie is not available when you try to rent it, then it should raise an
UnavailableException – you do NOT have to write this exception!

public class Movie {
String title;
int year;
Boolean available;
Customer customer;

1 mark for all variables, ½ if ONE missing, else 0

public Movie(String title) {
this.title = title;
available = true;
}
public Movie(String title, int year) {
this(title);
this.year = year;
}
public boolean isAvailable() {
return available;
}

1 mark
1 mark for initialising (here or above)
0 if no second Constructor
1 mark; ½ mark if both lines above repeated
(ok if just “this.title = title” repeated)

1 mark for method correctly done (else 0)

5

public void rent(Customer c) throws UnavailableException{
if (available) {
available = false;
customer = c;
} else {
throw new UnavailableException();
}
}
public void return() {
available = true;
customer = null;
}

½ mark for “throws ...”
1 mark
1 mark
1 mark
½ mark

1 mark

(b) Test loop.
(4 marks)
Our Movie rental system stores all its Movies in an Array:
Movie[] movies = new Movie[MAX_MOVIES];
Write a loop (use whatever type of loop you like) that loops through the movies array and
prints the title of movies, and ―available‖ if it is available OR the name of the Customer for any
movie that is out on loan. Print one entry per line.
For example, the output may look like this:
Avatar: available
The Terminator: on loan to Lawrence
Titanic: on loan to Andy
Aliens: available

for (Movie m : movies) {
1 mark for correct loop format
System.out.print(m.getTitle() + “: “);
1 mark for use of accessor
if (m.isAvailable()) {
1 mark for “if “+ correct condition
System.out.println(“available”);
} else {
System.out.println(“on loan to “ + m.getCustomer().getName()); 1 mark
}
}
Any loop construct is OK (if correct)
--- e.g. for (int i; i
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Create Date                     : 2010:10:11 20:07:34
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