UNIVERSITY OF OTTAWA

FACULTY OF ENGINEERING

SCHOOL OF INFORMATION TECHNOLOGY AND ENGINEERING

CSI1102/CSI1502A

Examination

April 2004

Examiners:

Dr. Diana Inkpen (CSI1102 Groups A, D)

Dr. Herna L Viktor (CSI1102 Groups B, C)

Dr. Fadi Malek (CSI1502A)

Total marks: 74

Duration: 3 hours

Total number of pages: 18

Important Regulations:

1. Students are not allowed to bring in any notes.

2. No calculators are allowed.

3. No electronic equipment is allowed, including mobile phones and laptop computers.

4. Student identification cards (or another photo ID with signature) are required.

5. An attendance sheet shall be circulated and should be signed by each student.

6. Please answer all questions on this paper, in the indicated space.

7. All questions are related to the Java object-oriented language.

Part A : [15 marks, 1 mark for each question]

State whether the following statements are True or False. Use the answer sheet provided below to indicate your answer.

1. An inner class cannot have static instance variables.

2. Static instance variables cannot be private.

3. A static method cannot refer to an instance variable in the same class.

4. The garbage collector is the mechanism in Java used to automatically free allocated memory.

5. The this reference always refers to the current executing object.

6. An array index cannot be a float, double, boolean or String.

7. Consider an int array named myarray which consists of 5 elements. Suppose you want to swap the 3^rd and 4^th elements in the myarray. The following code will accomplish the swap.

myarray[3] = myarray[4];

myarray[4] = myarray[3];

8. In black-box testing, the tester should have a detailed knowledge of how the program is implemented so that he/she can more carefully identify what portion(s) of the software are leading to errors.

9. Consider the following code fragment.

public class X extends Y

{

private int y;

public X()

{

y = 10;

super( );

}

… }

The instruction super( ); as located in the code fragment above, causes the constructor of class Y to be invoked.

10. Java does not support multiple inheritance, but some of the abilities of multiple inheritance are available by using public rather than protected or private modifiers.

Questions 11, 12, 13, 14 and 15 refer to the following UML diagram:

11. The Line class and the Shape class are in an aggregation relation.

12. The penColour variable is not inherited by the Line and Rectangle classes.

13. The fillColour variable should ideally be declared as public, to enforce encapsulation.

14. The draw() method is overloaded.

15. The draw() method in the Shape class should be abstract.

. Answers: Part A

Question	Answer
1.	True
2.	False
3.	True
4.	True
5.	True
6.	True
7.	False
8.	False
9.	False
10.	False
11.	False
12.	False
13.	False
14.	False
15.	True

Part B: [15 marks, 1 mark for each question]

Indicate which one of the following choices is correct. (Note: Only one of the answers is correct.) Use the answer sheet provided below to indicate your answer.

1. Which one of the following statements is correct?

1. An enclosing class can access data in the nested class if the data is declared private.
2. A static modifier can be applied either to a variable or a method, but not both.
3. A static nested class can reference instance variables or methods defined in the enclosing class.
4. None of the above

2. What is the value of counter after the following statements have been executed?

int counter = 0;

for (int x = 3; x <= 7; x = x + 4) {

for (int y = 1; y < x; y++) {

counter = counter + (x*y);

}

}

a. 9

b. 156

c. 214

d. 868

3. What are the values of a and b after the following loop has been executed?

int a = 0;

int b = 0;

for (a=0; a<10 && b<20; a=a+2) {

a = a + b;

b = b + a + 1;

}

a. a is 10, and b is 16

b. a is 28, and b is 45

c. a is 30, and b is 45

d. a is 12 and b is 16

4. Suppose somebody's height in inches is stored in a variable h. Which one of the following commands will correctly translate this height into feet-and-inches terminology? (Note that one foot contains 12 inches, so somebody who is 74 inches tall is usually said to be “6 feet and 2 inches”).

a. int feet = h/12;

int inches = (h - feet*12)/12;

b. double feet = h/12;

int inches = h%12;

c. int feet = h%12;

int inches = h;

d. int feet = h/12;

int inches = h%12;

5. What are the values of x and y after the following statements have been executed?

int x =8;

int y = 4;

x = y++ - 2;

a. x=2, y=4

b. x=2, y=5

c. x=3, y=5

d. x=3, y=4

6. For the following code fragment, suppose list is an int array that stores only positive int values. Which one of the tasks written below is accomplished when this code is executed?

int x = 0;

for (int j=0; j < list.length; j++)

if (list[j] > x)

x = list[j];

a. it stores the smallest value in list (the minimum) in x

b. it stores the largest value in list (the maximum) in x

c. it stores every value in list, one at a time, in x, until the loop terminates

d. it counts the number of elements in list that are greater than x

e. it counts the number of elements in list that are less than x

7. Suppose you want to initialize a String array names to store the three Strings "Good", "Luck" and "Today". The only syntactically valid statement to accomplish this is :

a. String names = {"Good", "Luck", "Today"};

b. String[ ] names = {"Good", "Luck", "Today"};

c. String[ ] names = new String{"Good", "Luck", "Today"};

d. String names[3] = {"Good", "Luck", "Today"};

e. String names; names[0] = "Good"; names[1] = "Luck"; names[2] = "Today";

8. A bad programming habit is to build an initial program and then spend a great deal of time modifying the code until it is acceptable. This is known as

a. the prototyping approach

b. the waterfall model

c. iterative development

d. the recursive approach

e. the build-and-fix approach

For questions 9 and 10, use the following partial class definitions:

public class A1

{

public int x;

private int y;

protected int z;

…}

public class A2 extends A1

{

protected int a;

private int b;

…}

public class A3 extends A2

{

private int q;

…}

9. Which of the following is true with respect to A1, A2 and A3?

a. A1 is a subclass of A2 and A2 is a subclass of A3

b. A1 and A2 are both subclasses of A3

c. A3 is a subclass of A2 and A2 is a subclass of A1

d. A2 and A3 are both subclasses of A1

e. A1, A2 and A3 are all subclasses of the class A

10. Which of the following lists of instance data are accessible in A3?

a. x, y, z, a, b, q

b. a, b, q

c. a, q

d. x, z, a, q

e. x, a, q

11. Indirect recursion happens when:

a. a method calls itself

b. a method calls another method that calls the initial method

c. a method is overloaded

d. a method is abstract

12. A queue is a data structure of the type:

a. last-in last-out

b. first-in first-out

c. last-in first-out

d. first-in last-out

13. Given the following method, what value does recur(3,6) return?

public int recur(int x, int y)

{

if (x == y) return y;

else return recur(x, y-1) + 1;

}

a. 3

b. 12

c. 6

d. 8

14. A linked list is:

a. a dynamic data structure

b. a static data structure

c. a primitive data type

d. added both a static and dynamic data structure, depending on the data type used

e. all of the above

15. Infinite recursion happens when, for example:

a. there is more than one base case

b. a method calls itself with the same parameter values

c. a condition in an if statement is never false

d. none of the above

Answer: Part B

Question	Answer
1.	D
2.	B
3.	D
4.	D
5.	B
6.	B
7.	B
8.	E
9.	C or D
10.	D
11.	B
12.	B
13.	C
14.	A
15.	B

Part C : [15 marks, 1 mark for each question]

Complete the following sentences by filling in the missing words. Use the answer sheet provided below to indicate your answer.

1. A class can simulate multiple inheritance by implementing more than one ……

2. A …….. variable is shared among all instances of a class.

3. A ……..class represents a primitive value so that it can be treated as an object.

4. When an object is passed to a method, the actual and formal ……. become aliases of each other.

5. The ………. method of a class cannot have a return type, not even void.

6. Consider an array declaration int[] height = new int[11]; The value of height.length is equal to ……

7. In Java, an ArrayList is a ……… data structure.

8. A ……….. reference can refer to different types of objects over time.

9. A class that cannot be instantiated is called …..

10. The …..…. visibility modifier provides the best possible encapsulation that permits inheritance.

11. An ….…. is a collection of data and the particular operations that are allowed on that data. It has a name, a domain of values and a set of operations that can be performed.

12. Any recursive definition must have a non-recursive part, called the ........... case, that permits the recursion to eventually end.

13. In a stack data structure we store data at the top of the stack using the push() method and we take data out from the ......... of the stack using the pop() method.

14. If a method throws an exception object of a checked type of exception, the method has to declare it by adding the keyword …………. to its signature.

15. UML diagrams are very useful in the ……….. stage of the process of developing a software system.

Answer: Part C

Question	Answer
1.	Interface
2.	Static
3.	Wrapper
4.	Parameters or arguments
5.	Constructor
6.	11
7.	Dynamic
8.	Polymorphic
9.	Abstract
10.	Protected
11.	ADT or abstract data type
12.	Base
13.	Top
14.	Throws
15.	Design

PART D: [29 marks]

1. Consider the following code fragment that represents a set of classes keeping track of sport statistics.

public class Players

{ public static void main (String [] args)

{

BaseballStats player1;

FootballStats player2;

player1 = new BaseballStats ("Sal Runner", "Phillies");

player2 = new FootballStats ("Mel Rogers", "Redskins");

player1.score();

player2.score();

player1.getHit();

player2.gainYards(15);

System.out.println (player1);

System.out.println ();

System.out.println (player2);

}

}

public abstract class PlayerStats

{

protected String player, team;

protected int score;

public PlayerStats (String playerName, String teamName)

{

player = playerName.substring(0, 5);

team = teamName;

score = 0;

}

public int getScore()

{

return score;

}

public abstract void score();

public String toString()

{

String result = "Player: " + player;

result += "\nTeam: " + team.toUpperCase();

result += "\nScore: " + score;

return result;

}

}

public class BaseballStats extends PlayerStats

{

protected int hits, errors;

public BaseballStats (String player, String team)

{

super (player, team);

hits = 0;

errors = 0;

}

public void score()

{

score += 1;

}

public void getHit()

{

hits += 1;

}

public void commitError()

{

errors += 1;

}

public String toString()

{

String result = super.toString();

result += " Hits: " + hits;

result += "\nErrors: " + errors;

return result;

}

}

public class FootballStats extends PlayerStats

{

protected int yards;

public FootballStats (String player, String team)

{

super (player, team);

yards = 0;

}

public void score()

{

score += 6;

}

public void gainYards (int numYards)

{

yards += numYards;

}

public String toString()

{

String result = super.toString();

result += "\nYards: " + yards;

return result;

}

}

What output is produced when Players.class is executed? [10]

Part D, Question 1 [10 marks]

2. What subset of the outputs, as listed in the window below, will the following program produce? Indicate the correct choices by choosing “Yes” for the messages that are printed by the program and “No” for the messages that are not printed, in the answer window below. [6]

public class CreateExceptions

{

public static void main (String[] args)

{

try

{

TestException Obj1 = new TestException();

System.out.println (“Enter level 0”);

Obj1.divide();

System.out.println (“Another message level 0”);

}

catch(ArithmeticException e)

{

System.out.println(e.getMessage());

}

System.out.println ("Exit level 0.");

}

}

public class TestException

{

public void divide()

{

System.out.println ("Enter level 1");

int N = 25, M = 0;

int z = N / M;

System.out.println ("Exit level 1");

}

}

Part D Question 2 [6]

1 mark for each correct answer

3. Suppose current and newNode are references to Node objects. Assume current currently refers to a specific node in a single-linked list and newNode refers to an unattached Node object. The following code fragment attempt to insert newNode behind current in the list. However, it contains two errors.

// assume each node has a reference field called “next”

// assume “next” refers to a subsequent node if there is one

newNode.next = current;

current.next = newNode.next;

Provide the correct code to accomplish this task. [4]

Part D, Question 3 [4]

1 mark for each “program code”; e.g. current.next

newNode.next = current.next; 2 marks

current.next = newNode; 2 marks

4. What output is produced when the following program is executed? [9]

public class Example

{ public static void main (String[] args)

{

String s = "http://www.BELL.ca/index.html";

URL web = new URL(s);

System.out.println(web.cool(s));

web.write();

System.out.println();

String u = "www.MAGMA.Cola.ca/index.html";

web = new URL(u);

System.out.println(web.cool(u));

web.write();

System.out.println();

String v = "ftp://www.OTTAWA.ca";

web = new URL(v);

System.out.println(web.cool(v));

web.write();

}

}

public class URL

{

public String service;

public String host;

public URL() {}

public URL (String url)

{

cool(url);

setURL(url) ;

}

void setURL(String s)

{

int i = s.indexOf("://");

if (i<0)

{

service = "http";

s = s.substring(0);

}

else

{

service=s.substring(0,i);

s = s.substring(i+3);

}

i = s.indexOf('/');

if (i<0)

host=s;

else

host = s.substring(0,i);

}

public String cool (String S)

{

int i; char c;

String res = " ";

for (i = 0; i <= S.length()-1; i++)

{

c = S.charAt(i);

if (c <= 'Z' && c >= 'A')

res = res + (char)((int)c + (int)'a' - (int)'A');

else

res = res + c;

}

return res;

}

public void write()

{

System.out.println("service=" + service);

System.out.println("host=" + host);

}

}

Part D, Question 4 [9]