CS 177 Spring 2009 Final Exam

Transcription

1 CS 177 Spring 2009 Final Exam There are 60 multiple choice questions. Each one is worth 4 points. The total score for the exam is 240. Answer the multiple choice questions on the bubble sheet given. Fill in the Instructor, Course, Signature, Test, and Date blanks. For Instructor put your RECITATION INSTRUCTOR S LAST NAME GIVEN BELOW. For Course put CS 177. For Test put final. Fill in the bubbles that correspond to your name, section and Student ID in the bubble sheet. For your section number, use the SECTION NUMBER of your recitation section. Consult the following list: 001 FRI 07:30 HAAS G066 Pelin Angin 002 FRI 08:30 HAAS G066 Jackie Soenneker 003 FRI 10:30 HAAS G066 Ryan Phelps 004 FRI 02:30 HAAS G066 Yao Zhu 005 FRI 03:30 HAAS G066 Younsun Cho 006 FRI 12:30 HAAS G066 Tion Thomas 016 FRI 11:30 REC 117 Yi-Liu Chao For your student ID, use the 10 digit ID number on your student ID card. DO NOT USE YOUR SOCIAL SECURITY NUMBER! Exams without names will be graded as zero. Only the answers on the bubble sheet will be counted. The questions will be discarded. Recitation Section Number Recitation TA s Name Student Last Name Student First Name

2 Multiple Choice Questions (4 points each): 1. Which of the following is the equivalent of the StdIn.readInt() method? (a) Getting the first argument in the command line arguments using args[0] (b) StdIn.readString() followed by Integer.parseInt() (c) It is not possible to achieve the task this method does in any other way. (d) StdIn.readString() followed by Double.parseDouble() 2. Which of the following best explains the effect of piping two programs using the operator? (a) Both programs run faster. (b) The output from the first program is fed as input to the second program. (c) The input to the second program is read from the same file providing input to the first program. (d) The output from the second program is written to a file following the output of the first program. 3. How do we represent sound using the StdAudio class in Java? (a) As an array of double values between 0 and 1. (b) As an object of the StdAudio class. (c) As an array of double values between -1 and 1. (d) There is no way to represent sound in Java. 4. Which of the following methods of the StdAudio class is used to play the sound from a file? (a) save(string file, double[] a) (b) play(int[] file) (c) play(string file) (d) play(double file) 5. What does the following program do? public class Sum { public static void main( String[] args ) { int sum = 0; for (int i = 0; i < 10; i++) { int num = StdIn.readInt(); if ( num % 2 == 0 ) { sum += num; System.out.println( sum ); (a) Prints the sum of the ten numbers input by the user. (b) Prints the sum of the odd numbers from ten numbers input by the user. (c) Prints the average of ten numbers input by the user. (d) Prints the sum of the even numbers from ten numbers input by the user. 1

3 6. What is the effect of executing the following command? java Program1 > file.txt (a) Program1 is compiled. (b) The output from the program Program1 is printed to the console. (c) The program Program1 gets its input from the file file.txt. (d) The output from the program Program1 is redirected to the file file.txt. 7. What is the problem with the following program? public class Print { public static void main( String[] args ) { for (int i = 0; i < 10; i++) { int num = StdIn.readDouble(); System.out.println( num ); (a) Assigning the value returned by the StdIn.readDouble() to an int causes a compiler error due to loss of precision. (b) We cannot print a double value using System.out.println(). (c) There is no readdouble() method in the StdIn class. (d) We cannot declare the variable num in the for loop. 8. What does the following program do? public class Test { public static void main( String[] args ) { String file = "amazing.wav"; double samples[] = StdAudio.read(file); for ( int i = 0; i < samples.length; i++ ) { double amount = 2*Math.random() - 1; samples[i] += amount; if ( samples[i] > 1 ) samples[i] = 1; else if( samples[i] < -1 ) samples[i] = -1; StdAudio.play(samples); (a) Plays the sound in the file amazing.wav without changes. (b) Reverses the sound in the file amazing.wav. (c) Adds noise to the sound in the file amazing.wav. (d) Increases the volume of the sound in the file amazing.wav. 2

4 9. What does the following program do? public class Test { public static void main( String[] args ) { String file = "amazing.wav"; double[] sound = StdAudio.read(file); double temp; for( int i = 0; i < sound.length / 2; i++ ) { temp = sound[i]; sound[i] = sound[sound.length i]; sound[sound.length i] = temp; StdAudio.play(sound); (a) Increases the volume of the sound in the file amazing.wav. (b) Plays the sound in the file amazing.wav without changes. (c) Reverses the sound in the file amazing.wav. (d) Adds noise to the sound in the file amazing.wav. 10. What does the following program do? public class Test { public static void main( String[] args ) { String file = "amazing.wav"; double[] sound = StdAudio.read(file); double[] newsound = new double[sound.length/2]; for( int i = 0; i < newsound.length; i++ ) newsound[i] = sound[2*i]; StdAudio.play( newsound ); (a) Doubles the speed of the sound in the file amazing.wav. (b) Adds noise to the sound in the file amazing.wav. (c) Increases the volume of the sound in the file amazing.wav. (d) Lowers the speed of the sound in the file amazing.wav by a factor of two. 11. Which of the following statements is true for large input sizes when one compares the worst case running time of the sequential search algorithm to that of binary search? (a) Binary search is slower than sequential search. (b) Binary search and sequential search are equally fast. (c) Binary search is faster than sequential search. (d) We cannot determine a relationship between binary search and sequential search. 3

5 12. Here are some statements about inputs to the binary search algorithm. Which of these is true? (a) The algorithm only works on sorted lists of elements. (b) The algorithm only works on lists with a small number of elements. (c) The algorithm only works on unsorted lists of elements. (d) The algorithm works on both sorted and unsorted lists of elements. 13. Which of the following options correctly describes the ordering of binary search, sequential search, bubble sort and insertion sort in terms of worst case running time? (a) binary search < sequential search < bubble sort < insertion sort (b) binary search < bubble sort < insertion sort < sequential search (c) bubble sort = insertion sort < binary search < sequential search (d) binary search < sequential search < bubble sort = insertion sort 14. Consider the data types that can be handled by bubble sort, insertion sort, and bucket sort. Which of the following statements is not true? (a) Bucket sort can be used to sort any kind of comparable data. (b) All three sorts can be used to sort integers. (c) Bubble sort can be used to sort any kind of comparable data. (d) Insertion sort can be used to sort any kind of comparable data. 15. What algorithm does the following function implement? private static int algorithm(int[] array, int value){ int left = 0, right = array.length-1; while ( right >= left ){ int middle = (right+left)/2; if ( array[middle] == value ) return middle; else if ( array[middle] > value ) right = middle-1; else // array[middle] < value return -1; left = middle +1; (a) Bubble sort (b) Binary search (c) Sequential search (d) Insertion sort 4

6 16. Which of the following statements about control structures is true? (a) The body of a do-while loop will not necessarily be executed. (b) The body of a for loop will always be executed at least one time. (c) We can always convert a for loop into a while loop and vice versa. (d) Any if-else statement could be converted into a switch statement. 17. Let array be an array of 10 integers. What are its contents after the following loop? for ( int i = 0; i < array.length; i++ ) array[i] = i/2; (a) {0, 0, 1, 1, 2, 2, 3, 3, 4, 4 (b) {0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 (c) {0, 1, 2, 3, 4, 5, 6, 7, 8, 9 (d) {0, 2, 4, 6, 8, 10, 12, 14, 16, Let array be declared as follows: int[] array = {0, 1, 2, 3, 4; What are the contents of array after the following loop? for ( int i = 1; i < array.length; i++ ) array[i] += array[i-1]; Note: Pay attention to when each element is changed. (a) {0, 1, 3, 5, 7 (b) {0, 1, 2, 3, 4 (c) {0, 1, 2, 4, 8 (d) {0, 1, 3, 6, Consider the following code fragment. Let array be an array of type int. What is the relationship between the variable a and array? double a = 0; for ( int i = 0; i < array.length; i++ ) a += array[i]; a /= array.length; (a) a is the average of all elements in array. (b) a is the minimum of all elements in array. (c) a is the maximum of all elements in array. (d) a is the sum of all elements in array. 5

7 20. Given the following Java classes, what is the output when the main() method in the Test class is run? public class Bug { public void crawl() { System.out.println("crawling..."); public void fly() { System.out.println("flying..."); public class Spider extends Bug { public void fly() { System.out.println("can t fly..."); public void spin() { System.out.println("spinning web..."); public class Test { public static void main(string[] args) { Spider spider = new Spider(); spider.fly(); spider.crawl(); Bug bug = spider; bug.fly(); bug = new Bug(); bug.fly(); (a) can t fly... crawling... can t fly... can t fly... (b) can t fly... crawling... flying... flying... (c) can t fly... crawling... can t fly... flying... (d) This code has an error and will not compile. 6

8 21. What does it mean to override a method? (a) To write a method with the same name as another method but with different parameter types. (b) To call a method from an external library instead of from the same class. (c) To write a method in a child class that has the same name as a method in a parent class. (d) To exit a method with a return statement before the method terminates. 22. Why is it a good idea to hide member variables inside an object with the keyword private? (a) To make programming harder. (b) To keep access to member variables restricted to static methods. (c) To keep other objects from corrupting the values of the member variables in unexpected ways. (d) To tease other objects. 23. Which of the following class inheritance choices makes the most sense? (a) Mammal extends Tiger (b) Seed extends Apple (c) StreptococcusBacteria extends Thing (d) Violin extends StringedInstrument 24. What is a difference between static and non-static methods? (a) Static methods return primitive types and non-static methods return objects. (b) Non-static methods belong to a class, whereas static methods belong to objects. (c) Non-static methods can access member variables, but static methods cannot. (d) Static methods return a value and non-static methods have a void return type. 25. Consider the static method increment() below. public static void donothing(int i) { i = i + 2; How many times will the following for loop iterate? for (int i = 0; i < 10; i++) donothing(i); (a) 9 times (b) 3 times (c) 5 times (d) 10 times 7

9 26. What is the error in the following code? public class Person { private String name; public Person() { name = "Jeeves"; public static void printname() { System.out.println("What ho, " + name + "!"); public static void main(string[] args) { printname(); (a) Using the Person class without calling its constructor will cause a run-time error. (b) There is no error in the code. (c) Trying to access a private variable from a static method will cause a compiler error. (d) Trying to access a non-static variable from a static method will cause a compiler error. 27. What would be a valid return statement inside of a method with the following signature? public static double getsample(string sample) (a) return sample; (b) return a ; (c) return; (d) return 5.1; 28. Consider the error below. % java Bad Exception in thread "main" java.lang.arrayindexoutofboundsexception: 0 at Bad.compile(Bad.java:4) at Bad.main(Bad.java:7) This is an example of a (a) syntax error (b) compile-time error (c) null pointer error (d) run-time error 8

10 29. Which of the following is not a valid variable declaration in Java? (a) int 123abc; (b) int abc123; (c) int Abc; (d) int a_b_c; 30. Which of the following is not a true statement regarding Strings in Java? (a) String is an example of a primitive data type in Java. (b) A String contains a list of characters. (c) It is possible to determine the length of a String in Java. (d) The + operator can be used on String objects to concatenate them together. 31. What would the value of var be after the following code is run? boolean a = true; boolean b = false; boolean var =!((a &&!b) a); (a) true (b) Its value depends on user input. (c) false (d) There is a compilation error in the code. 32. Consider the following class file: public class Phone { public final int number = ; public Phone (int value) { number = value; public void DialNumber() { System.out.println("Dialing number: " + number); Which of the following best describes the compilation error that is present in this code? (a) The variable number is not within the scope of the DialNumber() method. (b) The variable number in the DialNumber() method must be of type String to be used in the System.out.println() method. (c) The final member variable number can only be assigned a value in the constructor of the class. (d) The final member variable number cannot be reassigned in the constructor since final variables can only be assigned a value once. 9

11 33. What will be printed to the screen as a result of running the following code: public static void main(string[] args) { String expression = "1" ; double value = Double.parseDouble(expression); double roundedvalue = Math.round(value); int integervalue = (int)value; System.out.println("Output: "); System.out.print("Original Value: " + value + "\nrounded Value: " + roundedvalue + "\ninteger Value: " + integervalue); (a) Output: Original Value: Rounded Value: Integer Value: 121 (b) Output: Original Value: \nRounded Value: 121.0\nInteger Value: 121 (c) Output: Original Value: Rounded Value: Integer Value: 120 (d) Output: Original Value: \nRounded Value: 121.0\nInteger Value: Which of the following statements about constructor methods is not true? (a) The code within a constructor is primarily used to initialize the member variables of an object. (b) You must always define a constructor method for your class or else Java will give a compiler error. (c) Invoking a constructor creates an instance of an object and returns a reference to that object. (d) A constructor is invoked when a program uses the new keyword. 35. What data type could be returned by method check() given that the following fragment of code is valid? if (check().equals("1")) System.out.println("Get sale."); else System.out.println("Go to next store."); (a) String (b) char (c) boolean (d) int 10

12 36. Consider the following class file: public class Money { private double amount; public Money (double initialamount) { amount = initialamount; public double addamount(int dollars, int cents) { String newamount = ""; newamount = newamount + dollars + "." + cents; double convertedamount = Double.parseDouble(newAmount); System.out.println("Converted amount = " + convertedamount); amount += convertedamount; return amount; Which set of the following statements provides the best categorization of the variables used in the Money class? (a) Member variables: amount, initialamount Argument variables: dollars, cents Local Variables: newamount, convertedamount (b) Member variables: newamount, convertedamount Argument variables: initialamount, dollars, cents Local Variables: amount (c) Member variables: amount Argument variables: initialamount, dollars, cents Local Variables: newamount, convertedamount (d) Member variables: initialamount, dollars, cents Argument variables: amount Local Variables: newamount, convertedamount 37. Suppose that f(n) is O(n 2 ) in Big Oh notation. Which of the following functions could be f(n)? (a) 2 n + 184n 2 (b) 5n 2 log n + 2 (c) 34n + 15n (d) 901n 3 6n 2 11

13 38. Consider the following class file: public class HDTV { private static int resolution = 0; public static int size = 0; public static void displaypicture() { System.out.println("Displaying picture at resolution: " + resolution ); public static void setresolution(int r) { resolution = r; public static void setsize(int s) { size = s; public static int getresolution() { return resolution; Which of the following statements would result in a compilation error? (a) HDTV.setResolution(720); (b) HDTV.resolution = 720; (c) int r = HDTV.getResolution(); (d) HDTV.size = 50; 39. What is the running time of binary search on an array with n elements in Big Oh notation? (a) O(n 2 ) (b) O(log n) (c) O(n log n) (d) O(n) 40. What happens if a class defines a method with the same name and parameters as a method in its superclass? (a) There is no problem because overriding methods is allowed. (b) The subclass method will be ignored. (c) The compiler automatically renames the subclass method. (d) The compiler gives an error. 12

14 41. Which one of the following statements about if statements is correct? (a) The conditional of an if statement must evaluate to the boolean type. (b) An if statement must include an else if statement. (c) An if statement must include an else statement. (d) None of the above is correct. 42. What does the following fragment of code print out? double x = -1; if ( x > 1) if ( x > 3 ) System.out.println("x is big."); else if( x > 2 ) System.out.println("x must be 3."); else { if (x < 0) System.out.println("x is too small."); else System.out.println("x is small."); (a) x must be 3. (b) x is small. (c) Nothing is printed out. (d) x is big. 43. What is the output of problem("bdcda")? public static void problem(string s) { int j = 0; char letter; for(int i = 0 ; i < s.length(); i++) { letter = s.charat(i); if (letter == a ) break; else if (letter == b ) continue; else if (letter == c ) j *= 2; else if (letter == d ) j++; System.out.println( j ); (a) 1 (b) 3 (c) 2 (d) 0 13

15 44. What is the output of the following code? public static void main(string[] args) { char initial = c ; switch (initial) { case j : System.out.print("John"); break; case c : System.out.print("Chuck"); case t : System.out.print("Ty"); break; case s : System.out.print("Scott"); default: System.out.print("All"); (a) JohnChuckTyScottAll (b) ChuckTy (c) Chuck (d) ChuckTyAll 45. Given the following code segment, what will be printed out? String s1 = new String("identical"); String s2 = new String("identical"); if( s1 == s2 ) System.out.print("Same1 "); else System.out.print("Different1 "); if( s1.equals( s2 ) ) System.out.println("Same2"); else System.out.println("Different2"); (a) Different1 Different2 (b) Same1 Different2 (c) Different1 Same2 (d) Same1 Same2 14

16 46. Suppose the size of array a passed into this method is 10. At most, how many times will the exchange() method be called? public static void sort(int[] a) { for (int i = 0; i < a.length; i++) { for (int j = i; j > 0; j--) { if (a[j-1] > a[j]) { exchange(a, j-1, j); else break; (a) 36 (b) 90 (c) 45 (d) How many int values can be held in the array declared below? int[][][] array = new int[5][4][1]; (a) 11 (b) 21 (c) 20 (d) Which of the following statements about constant values is not correct? (a) Constants can only be assigned a value once and will never change afterwards. (b) Private members can be declared as constants. (c) Static members cannot be declared as constants. (d) Constants are declared in Java with the final keyword 49. What is the index of the first element in an array? (a) 1 (b) 0 (c) It depends on the length of the array. (d) -1 15

17 50. What will the contents of numbers be after the following for loop is executed? int[] numbers = new int[5]; for(int i = 0; i < numbers.length; i++) numbers[i] = i*i; (a) {1, 4, 9, 16, 25 (b) {0, 1, 4, 9, 16 (c) {0, 0, 0, 0, 0 (d) {0, 1, 2, 3, What are the error(s) in the following code? String[] strings = new String[10]; for(int index = 0; index <= strings.length; index++) System.out.println(strings[index].length()); (a) The value of index goes past the last valid index in strings. (b) The code contains no error. (c) Both errors are present. (d) The elements of an object array should be initialized before they can be used. 52. Which of the following is not true about arrays? (a) The size of an array cannot change. (b) Everything in an array must have the same type. (c) An array is a data structure. (d) Arrays are never automatically filled with values when created. 53. What does the following code create? (Assume the first dimension is rows and the second dimension is columns). int[][] numbers = new int[3][]; for(int i = 0; i < numbers.length; i++) numbers[i] = new int[i+1]; (a) A two-dimensional array with 3 rows and 3 columns. (b) A ragged array with 3 rows, where the first row has 2 columns, the second row has 3 columns, and the third row has 4 columns. (c) This code will cause a run-time error. (d) A ragged array with 3 rows, where the first row has 1 column, the second row has 2 columns, and the third row has 3 columns. 16

18 54. Which is the correct way to get the Color object for the pixel at position (25, 30) from a Picture object called picture? (a) Color c = picture[25][30]; (b) Color c = picture[25][30].get(); (c) Color c = picture.get()[25][30]; (d) Color c = picture.get(25, 30); 55. Which is the correct way to get the blue intensity level from a Color object called color? (a) int blue = color.getrgb().getblue(); (b) int blue = getblue(color); (c) int blue = color.getblue(); (d) int blue = color[blue]; 56. What does the following code fragment do? Picture picture = new Picture(100, 100); for(int i = 0; i < picture.width(); i++){ for(int j = 0; j < picture.height(); j++){ Color c = new Color(255, 0, 0); picture.set(i, j, c); (a) Creates a 100x100 pixel picture that is completely blue. (b) Creates a 100x100 pixel picture that is completely red. (c) Shrinks an image down to 100x100 pixels. (d) Creates a mirror image of the original picture. 57. What does the following code fragment do? Picture p = new Picture("fish.jpg"); for(int i = 0; i < p.width(); i++){ for(int j = 0; j < p.height(); j++){ Color old = p.get(i, j); int r = old.getred(); int g = old.getgreen(); int b = old.getblue(); int x =.299*r +.587*g +.114*b; Color current = new Color(x, x, x); p.set(i, j, current); (a) Creates a blue-tinted version of fish.jpg. (b) Creates a rotated version of fish.jpg. (c) Creates a version of the file fish.jpg whose size has been reduced. (d) Creates a grayscale version of the file fish.jpg. 17

19 58. Which of the following is not true about colors and the Color class? (a) In the RGB model, (0,0,0) is the color white. (b) To use the Color class, you must import it using an import statement. (c) The Color class uses the RGB model. (d) In the Color class, each color component has an intensity value between 0 and Which of the following commands would you type into the terminal to execute a program whose source code is stored in YakAttack.java? (a) java YakAttack.class (b) java YakAttack (c) javac YakAttack (d) javac YakAttack.java 60. Which of the following statements regarding Java objects are true? I. Three common types of object methods are: constructors, accessors, and mutators. II. Objects contain members and methods; members are usually private while methods are usually public. III. A static method must be associated with a particular object. (a) I and II only (b) I and III only (c) I, II, and III (d) I only 18