202 COMP Summer 2006 School of Computer Science - Faculty of Science - McGill University
COMP 202 - Introduction to Computing 1 Final exam Version 1
July 3, 2006, 2:00 5:00 PM Instructor: Carlton Davis Last name ___________________________________ First name ___________________________________ Student ID ___________________________________
Instructions:
No notebooks, textbooks or calculators are allowed in this exam. Language translation dictionaries are permitted. All answers should be written on the exam sheets. Part marks are given for all questions; so, show your work and attempt all questions For section 1 (multiple choice) mark your answer in this front page. Read the questions carefully.
Grading
Section I: Multiple choice Question Your answer Mark /3 /3 /3 /3 /3 /3 /3 /3 /3 /3 Q1 Q2 Q3 Q4 Q5 Q6 Q7 Your mark:______ / 30 Q8 Q9 Q10
Section II: Short Problems Question Mark II.1 /9 II.2 /5 II.3 /10 II.4 /6
Your mark: ______ / 30
Section III: Programming Problem Question Mark III.1 / 15 III.2 /25
Your mark: ______/ 40
Your Exam Score: _________/ 100 COMP 202 Summer 2006 Final Exam Page 1 of 21
Section I: Multiple choice (3 points/question)
I.1) What is the output of the following code fragment? public class Test { static boolean b; public static void main(String [] args) { short hand = 42; if (hand < 50 && !b) hand++; if (hand > 50); else if(hand > 40) { hand += 7; hand++; } else --hand; System.out.println(hand); } } A. B. C. D. E. 41 43 50 51 It gives a compile error
I.2) A. B. C. D. E.
Which of the following is TRUE about protected variables in a given class? They are shared like static variables They cannot be changed once they have been assigned a value They can be accessed directly by subclasses They cannot be used as parameters None of the above
I.3) A. B. C. D. E.
Which of the following statement regarding the super keyword is INCORRECT? super can be used to invoke a superclass constructor super can be used to invoke a method in the base class super.super.p() can be used to invoked a method p() in the superclass's parent class super can be used to invoked a method in the superclass's parent class None of the above
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I.4) A. B. C. D. E.
Which of the following statement(s) is/are TRUE? A method can be overloaded in the same class A method can be overrided in the same class If a method overloads another method both methods must have the same signature and return type All the above None of the above
I.5)
Consider the following code fragment public class Test { public static void main(String[] args) { Object a1 = new A(); Object a2 = new Object(); System.out.println(a1); System.out.println(a2); } } class A { int x; public String toString() { return "A's x is " + x; } }
Which of the following is/are CORRECT? A. When executing System.out.println(a1), the toString() method of the Object class is invoked B. When executing System.out.println(a2), the toString() method of the Object class is invoked C. When executing System.out.println(a1), the toString() method in the A class is invoked D. All the above E. B and C only
I.6)
What does the following code fragment outputs? class A { private int num=10; }
class B extends A { public static void main(String [] args) { int x=5; COMP 202 Summer 2006 Final Exam
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B obj = new B(); x += obj.num++; System.out.println("x is: " + x +" num is: " + obj.num); } } A. B. C. D. E. x is: 16 num is: 11 x is: 15 num is: 10 x is: 15 num is: 11 x is: 16 num is: 10 Compile errors
I.7)
If Car is a subclass of Automobile and Automobile is a subclass of Vehicle, then which of the following statement(s) below is/are INVALID? 1) Vehicle V1 = new Car(); 2) Automobile A1 = new Car(); 3) Car C1 = new Automobile(); 4) Automobile A2 = (Automobile) (new Car()); 5) Car C2 = new Car(); 6) V1 = C2; 4 and 6 only 3 and 6 only 1, 2 and 3 All except 4 and 5 All except 5
A. B. C. D. E.
I.8)
If Country is parent class of City, Canada is an object of type Country and Montreal is an object of type City. If Country has a method called getArea() which returns an int and City has a method with the same name (getArea()) except that it returns a double. Which of the following holds? Montreal.getArea() returns a double Montreal.getArea() returns an int City.getArea() returns a double City.getArea() returns an int None of the above
A. B. C. D. E.
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I.9) A. B. C. D. E.
Which of the following is TRUE about the this keyword? Only a constructor for a class can use the this keyword to identify or to assign a value to a class field Any method within a class can use the this keyword to identify or to assign a value to a class field The this keyword can only be used to reference non-static class fields The this keyword can only be used to reference objects None of the above
I.10) Which of the following is TRUE about Java interfaces and abstract classes? A. B. C. D. E. interfaces contains only abstract methods but abstract classes can contain non-abstract methods A class can implement only one interface; similarly, a class can only have one abstract parent class interfaces are similar to abstract classes in that they both cannot be instantiated or be base classes All the above A and C only
Section 2: Short Problems (30 points)
II.1) Consider the following Java classes:
public class myQuestion { protected int a; protected int b; public myQuestion() { this.a = 0; this.b = 0; } public myQuestion(int x, int y) { this.a = x; this.b = y; } public myQuestion(int x) { this(); this.a = x; } public int enquire() { return this.a + this.b; } public int interrogate(int x) { COMP 202 Summer 2006 Final Exam Page 5 of 21
return (this.a + this.b)* x; } public void display() { System.out.println(this.a + " " + this.b); } } class myProblem extends myQuestion { protected int c; public myProblem() { this.c = 0; } public myProblem(int x, int y, int z) { super(y,z); this.c = x; } public myProblem(int x, int y) { super(x,y); } public myProblem(int x){ this.c = x; } public int enquire() { this.c = this.a * this.b; return this.c; } public void display() { System.out.println(this.a + " " +this.b + " " +this.c); } } a) What does the following code fragment outputs? (3 points) myProblem p=new myProblem(20,2); System.out.println(p.enquire()); System.out.print(p.interrogate(2) + " "); p.display();
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b)
What does the following code fragment outputs? (3 points) myProblem p=new myProblem(20,2,4); p.display(); p.enquire(); p.display();
c)
What does the following code fragment outputs? (3 points) myProblem p = new myProblem(10); myQuestion q = new myQuestion(10); System.out.print(p.enquire() + " "); p.display(); System.out.print(q.enquire() + " "); q.display();
II.2)
What is the exact output of the following code? (5 points)
class Test { private int x; private int y; Test(int x, int y) { this.x = x; this.y = y; COMP 202 Summer 2006 Final Exam
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} void myMethod(int[] arrayA) { arrayA[0] = x--; arrayA[1] = ++y; arrayA[2] = x; } public static void main(String [] args) { Test A = new Test(10, 5); int[] array = {1, 2, 3}; try { int num=5; for(int i=0; i<5; i++) { A.myMethod(array); num = num/num-i; int j=0; System.out.print("The array elements are: "); while(j < array.length) { if(j == 2) System.out.print(array[j] +"\n"); else System.out.print(array[j] +", "); j++; } //End of while loop } //End of for loop } //End of try block catch(ArithmeticException e) { System.out.println("An illegal operation occured"); } } //End of main method } //End of class Test
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II.3) The following code fragment has 10 errors. The errors may be compile-time errors or run-time errors that occur when the methods are executed. Identify the errors and say what need to be done to fix them. You can indicate your answer on the respective lines or use the space provided below. (10 points) import java.util.*; public abstract class A { private String name; //Line 1 //Line //Line 3 4
A(String n) { //Line 6 name = n; //Line 7 } public String getName() { //Line 9 return name; } public String myMethodA(String s, double b); //Line 12 } class B extends A { //Line 16 private int ID; //Line 17 B(int id) { //Line 19 super(); //Line 20 ID = id; //Line 21 } public int getID() { //Line 23 return ID; //Line 24 } public String myMethodA(String str, double value) { //Line 27 return str.charAt(0)+str.charAt(1); //Line 28 } } class C extends A,B { C() { super(); } //Line 32 //Line 34
public String myMethodA(String t, double a) { //Line 37 return t.substring(1, t.length()); //Line 38 } public static void main(String arg[]) { //Line 41 int id; //Line 42 String name; //Line 43 A objC = new C(); //Line 44 ArrayList<A> arraylist = new ArrayList<A>(); //Line 46 COMP 202 Summer 2006 Final Exam Page 9 of 21
Scanner scan = new Scanner(System.in); //Line for(int i=0; i<=5; i++) { //Line System.out.print("Please enter the name: "); //Line try { //Line name = scan.nextLine(); //Line A objA = new A(name); //Line arraylist.add(objA); //Line } catch(NoSuchElementException) { //Line System.out.println("No input read"); //Line } System.out.print("Please enter the ID: "); //Line Scanner scan1 = new Scanner(System.in); //Line try { //Line id = scan1.nextInt(); //Line B objB = new B(id); //Line arraylist.add(objB); //Line } catch(InputMismatchException) { //Line System.out.println("ERROR: an integer is required"); } }
47 48 49 50 51 52 53 55 56 58 59 60 61 62 63 65 //Line 66
for(int x : arraylist) //Line 70 System.out.println("name is: "+ x.getName()+" and ID is: "+ A.getID()); //Line 71 and 72(above) } }
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II.4) Write code for a recursive method named find which takes two strings theString and str which returns true if str is contained in theString, and false otherwise. Note: Only code for the method is required; you don't need to provide other necessary code for a class. (6 points)
Section III: Programming problem (40points)
III.1) (15 points) In the question, you are required to implement 3 classes that can be used to maintain a database of media items in a library. These classes will represent generic media items, CDs and DVDs. All media items have the following characteristics (instance variables): a title a variable to track if that item is currently present in the collection. (Use a boolean for this value) a playing time (a double) All media items have the following behaviors (methods): get the title get if the item is present in the collection set the status of the item (status is in or out of the collection) get the playing time (note that playing time should be a double) a toString method (which gives all relevant information about the media item) CDs and DVDs have all of the characteristics and behaviors of media items. COMP 202 Summer 2006 Final Exam Page 12 of 21
CDs have the following additional characteristics and behaviors an artist a number of tracks a toString method (which gives all relevant information about the CD) DVDs have the following additional characteristics and behaviors a rating (example G, PG PG-13 or R) a way to get the total playing time of the DVD. Note this should override MediaItem's method for getting the playing time a toString method (which gives all relevant information about the DVD) You are to implement 3 classes, MediaItem, CD and DVD; CD and DVD must all extend MediaItem. You must provide one constructor for each class that takes in parameters to set all instance variables. You should make all the instance variables private in all classes. You are not to repeat instance variables from MediaItem in the classes that extend it. You will have to override some of the methods in MediaItem in the subclasses.
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III.2) (25 points) In this question, you are to assume that information relating to the media items described in III.1 above are stored in a file. Each line in the file contains the record for a media item. Each media item record starts with the follows: String1;title;inCollection;playingTime where String1 is "CD" or "DVD" depending on whether the record is for a CD or a DVD. title is a string which indicates the title of the CD or DVD; inCollection is an integer value which is equal to 1 if the media item is in collection and 0 otherwise. Whereas, playingTime is a double which represents the playing time of the media item. If the media is a CD, the full record has the following form: String1;title;inCollection;playingTime;artist;numOfTracks where the last two fields is a string and an integer which represents the name of the artist and number of tracks (the CD contains) respectively. If the media is a DVD, the full record has the following form: String1;title;inCollection;playingTime;rating where the last field is a string which indicates the rating. You are required to implement a class called MediaRecord, which has the following methods: void menu(): which prints a menu giving the user the option to enter `s' to search for a media item, or `q' to quit. menu() should also prompt the user to enter a command. char getCommand() : should read the command the user enters, checks if the command is valid and returns it only if it is valid. void search(ArrayList<MediaItem> arraylist): should prompted the user to enter the title of a media item, get the user's input and search the array list (the input parameter) for a media item with the requested title. If a media item is found with the given title, all relevant information related to the media item should be printed. If no item with the requested title is found, a message should be printed indicating that no media item with the given title was found. void processData(String fileName,ArrayList<MediaItem> arraylist) : This method should read data from a file with the given filename (the first paramether). The format of the data in the file is as indicated above. The data from the file should be read and use to create corresponding media item objects, which should be stored in the array list (the second parameter of the method). void writeDataToFile(ArrayList<MediaItem> arraylist): Should write the record relating to the media item objects in the array list (the parameter of the method) to a file called record.dat. The record should be in the format indicated above. main method: The main method should accept a filename as a command line parameter. In addition, main should create an array list for storing objects of type MediaItem, and call the methods outlined above such that data from the file (the filename entered as a command line parameter) is read and the data used to create corresponding media item objects, and the objects stored in the array list; after which the menu is printed and the user consequently prompted to enter a command, and the command executed. The above cycle (command and execution of the command) should continue until the command is `q', which should cause the data related to the media item objects in the array list to be written to a file. You program should handle ArrayIndexOutOfBoundsException, NoSuchElementException, InputMismatchException, FileNotFoundException and IOException exceptions appropriately in the relevant methods, such that, for example, the program should not crash if no command line parameter is supplied when the program starts, or if an incorrect input is supplied, or the COMP 202 Summer 2006 Final Exam Page 17 of 21
file is non-existence. Note: You can assume that the class files for question III.1 (ie MediaItem.class, CD.class and DVD.class) are available in the same directory as your program; therefore, you can use any of the methods of these classes.
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