Multiple Choice Questions Consider the following method and code segment.

Transcription

1 Multiple Choice Questions Consider the following method and code segment. public static double jack(double seed) seed = seed + Math.PI; seed = Math.sqrt(seed); seed = seed - (int) seed; return seed; double seed = ; for (int k = 1; k < 10; k++) seed = jack(seed); What values are returned as a result of executing the code segment? (A) Ten double values such that for each x 0 < x < 1 (B) Ten double values such that for each x 0 < x <= 1 (C) Ten double values such that for each x 0 < x < Math.PI (D) Ten double values such that for each x 0 < x <= Math.PI (E) Ten double values such that for each x 1 < x < Math.PI 02. Consider the following method. // precondition: m > 0 public static int mystery(int m) int counter = 0; for (int p = 1; p < m; p++) for (int q = p; q < m; q++) counter++; return counter; What value is returned as a result of the call mystery(8)? (A) 21 (B) 28 (C) 36 (D) 81 (E) 90

2 03. Consider the following code segment. int p = <some int value> int q = <an int value, such that p > q> int r = q - p + 1; for (int k = 1; k <= 300; k++) int rndnum = (int) (Math.random() * r) + p; System.out.print(rndNum + " "); What is the range of random numbers that can be assigned to rndnum? (A) [0.. q-r] (B) [0.. r] (C) [p.. q-r] (D) [q.. p] (E) [p.. q] 04. Today's airports do not process their data (luggage and passengers) in an Objected Oriented Manner. Imagine a future airport where passengers and luggage are handled as follows: 1. Passengers enter a closed hallway restricted to their flight destination. 2. Passengers check in their luggage with an agent who only handles one destination. 3. The luggage is placed on a conveyer belt dedicated for one destination only. Such a future airport resembles Object Oriented Programming by using which one of the following OOP features? (A) encapsulation (B) inheritance (C) composition (D) polymorphism (E) debugging

3 05. Consider the following code segment. int[][] m = 11,12,13,14,15, 16,17,18,19,20, 21,22,23,24,25, 26,27,28,29,30, 31,32,33,34,35 ; for (int r = 0; r < m.length; r++) for (int c = 0; c < m[0].length; c++) if (r == c) System.out.print(m[r][c] + " "); else System.out.print("00 "); Which is printed as a result of executing the code segment? (A) (B) (C) (D) (E)

4 base-10 equals what number in base-5? (A) (B) (C) (D) (E) Consider the following program segment. String s1 = "ABCD"; String s2 = ""; for (int k = 1; k < s1.length(); k++) s2 += s1.substring(k); System.out.println(s2); What will be output when the program segment executes? (A) D (B) CD (C) CDD (D) BCDCDD (E) ABCDBCDCDD 08. Consider the following code segment. ArrayList<String> animals = new ArrayList<String>(); animals.add("giraffe"); animals.add("tiger"); animals.add("elephant"); animals.add("wildebeest"); animals.add("aardvark"); animals.remove(1); animals.remove(3); for (String animal: animals) System.out.print(animal + " "); What is printed as a result of executing the code segment? (A) Giraffe Elephant Wildebeest (B) Tiger Wildebeest Aardvark (C) Giraffe Elephant Aardvark (D) Tiger Elephant Aardvark (E) Tiger Elephant Wildebeest

5 Free Response Question 1. Part (a). Write method fromhextobin, which is described as follows. Method fromhextobin converts the base-16 argument number to its base-2 equivalent. The base-2 number is returned. In completing method fromhextobin you can use the following table, which details the unique relationship between base-16 and base-2 numbers. Every single base-16 digit corresponds to four base-2 digits. Base a b c d e f Base Complete method fromhextobin below. // precondition: hexnum is a String of characters, which represents // a correct base-16 number. // postcondition: returns a String of characters, which represents // the base-2 number equivalent of hexnum. public static String fromhextobin(string hexnum) Part (b). Write method frombintodec, which is described as follows. Method frombintodec converts the base-2 argument number to its base-10 equivalent. The base-10 number is returned. Complete method frombintodec below. // precondition: binnum is a String of characters, which represents // a correct base-2 number. // postcondition: returns an int value, which represents // the base-10 number equivalent of binnum. public static int frombintodec(string binnum) Part (c). Write method fromhextodec, which is described as follows. Method fromhextodec converts the base-16 argument number to its base-10 equivalent. The base-10 number is returned. In writing method fromhextodec you may call methods fromhextobin and frombintodec, which are specified in Part (a) and Part(b), whether the methods are implemented correctly or not. Complete method fromhextodec below. // precondition: hexnum is a String of characters, which represents // a correct base-16 number. // postcondition: returns an int value, which represents // the base-10 number equivalent of hexnum. public static int fromhextodec(string hexnum)

6 Free Response Question 2. Consider the following incomplete declaration of a Matrix class. The intent of the Matrix class is to facilitate mathematical operations performed on two-dimensional, rectangular arrays. Matrix objects can be constructed with row and column size information only or with a provided integer array parameter. A Matrix class can have many useful operations. For this question the focus will be on writing methods for matrix multiplication and matrix display. Method multiply takes two Matrix objects and returns the product. Method oksize is a private helper method for method multiply and determines if the provided Matrix objects can be multiplied. You will also need to redefine the tostring method to display the elements of a Matrix object. public class Matrix private int twod[][]; private int numrows; private int numcols; public Matrix(int r, int c) numrows = r; numcols = c; twod = new int[numrows][numcols]; public Matrix(int array[][]) twod = array; numrows = twod.length; numcols = twod[0].length; public String tostring() /* to be implemented by part (a) */ private boolean oksize(matrix m1, Matrix m2) /* to be implemented by part (b) */ public void multiply(matrix m1, Matrix m2) /* to be implemented by part (c) */ // other methods used by the Matrix class

7 Part (a). Redefine the tostring method as discussed earlier. Method tostring must return a string that will display a Matrix in two-dimensional array format. The following table shows the result of several different calls made by System.out.println(/* Matrix Object */) to the tostring method based on the String argument of the constructor. The code segment below is part of a client program that constructs and displays three Matrix objects. Code segment in client program using the Matrix class int[][] mat1 = 1,2,3, 4,5,6, 7,8,9; int[][] mat2 = 1,0,0, 0,1,0, 0,0,1; Matrix m1 = new Matrix(mat1); Matrix m2 = new Matrix(mat2); Matrix m3 = new Matrix(3,3); System.out.println(m1); System.out.println(m2); System.out.println(m3); m3.multiply(m1,m2); System.out.println(m3); Execution Output Complete method tostring below. // precondition: twod is a nonempty two-dimensional integer array // postcondition: returns a string in rectangular matrix format. public String tostring()

8 Part (b). Matrix multiplication involves a process of adding the products of elements of rows in one matrix times corresponding elements of columns in a second matrix. This process is demonstrated by the matrix multiplication example below. a b e f ae + bg af + bh c d * g h = ce + dg cf + dh It is not necessary that matrices are square matrices or identical matrices. Two matrices can be multiplied as long as the number of columns in the first matrix are equal to the number of rows in the second matrix. The next example involves a 2 x 3 matrix and a 3 x 2 matrix. a b c g h ag + bi + ck ah + bj + cl d e f * i j = dg + ei + fk dh + ej + fl k l Observe that the 2 x 3 matrix is multiplied by a 3 x 2 matrix and creates a 2 x 2 matrix product. A general formula can be stated about the matrix multiplication, which is: An a x b matrix times a b x c matrix becomes an a x c matrix. This formula shows that there are special size requirements for all three matrices involved in the multiplication process. The column size (b) of the first matrix must be the same as the row size (b) of the second matrix. Furthermore, the product matrix must have row size (a) and column size (c). Write method oksize, which is described as follows. Method oksize is used to see if the three matrices involved in multiplication follow the correct rules of row and column size. Method oksize returns true if the number of column of m1 equals the number of rows of m2 and the product matrix has the same number of rows as m1 and the same number of columns as m2. Complete method oksize below. // precondition: m1 and m2 are not null // postcondition: returns true if m1 columns equals m2 rows and // m1 rows equals object's rows and m2 columns // equals object's columns private boolean oksize(matrix m1, Matrix m2)

9 Part (c). Write method multiply as described earlier. In writing method multiply, you may call method oksize, as specified in part (b). Assume that oksize works as specified, regardless of what you wrote in part (b). Complete method multiply below. // precondition: m1 and m2 are not null // postcondition: the product of the m1 and m2 is stored in the // current object, if possible, otherwise the // current object remains unchanged public void multiply(matrix m1, Matrix m2)