Mock Final Exam with Solution

Transcription

1 M105: Introduction to Programming with Java Mock Final Exam with Solution Fall 2012 / 2013 Question One: [15 marks: 1.5 each] Choose the correct answer and write it on the external answer booklet. 1. The command executes a Java application. a. javac b. java c. run d. none of the above 2. Which of the following cannot cause a syntax error to be reported by the Java compiler? a. Mismatched { b. Missing */ in a comment that begins with /* c. Missing ; d. An extra blank line 3. Which statement prints the integer value 99 left justified with a field width of 7? a. System.out.printf( "%d", 99 ); b. System.out.printf( "%7d", 99 ); c. System.out.printf( "%-7d", 99 ); d. System.out.printf( "%d7", 99 ); 4. Which of the following primitive types is never promoted to another type? a. long b. boolean c. double d. b and c 5. Consider the array: int[] p = {7, 0, -12, 9, 3, 10, 13; The value of p[p[6] - p[5]] is: a. 3 b. 7 c. 9 d A default constructor has how many parameters? a. 0 b. 1 c. 2 d. a variable number. 7. Set methods are also commonly called methods and get methods are also commonly called methods. a. query, mutator b. accessor, mutator c. mutator, accessor d. query, accessor Page 1 of 6

2 8. Inheritance is also known as the: a. knows-a relationship. b. has-a relationship. c. uses-a relationship. d. is-a relationship. 9. Which of the following should usually be private? a. attributes (instance variables) b. methods c. constructors d. classes 10. Declaring the method main as allows the JVM to invoke it without creating an instance of the class. a. public b. static c. void d. final Question Two: [ marks] Write a Java method called StopAtOne that has an integer argument called max. The method prints on the screen all the numbers from max to 1, one per line. Example: Assume that max = 4, The output should be: Question Three: [ marks] Trace the following programs and give their exact output. a. [ marks] public class Trace1M { static int num1 = 1; static double num2 = 2; public static void main(string[] args) { int num1 = 9; System.out.println( tryit() ); System.out.println( tryit(num1) ); System.out.println( tryit(trace1m.num1) ); tryit(num1, num2); // end main public static int tryit() { return tryit(5) + 2; public static int tryit(int num) { return num + num1++; public static void tryit(int num1, double num2) { System.out.printf("%.0f\n", num1 * num2); // end class Page 2 of 6

3 b. [ marks] import java.util.arrays; public class Trace2M { public static void main(string[] args) { String mock = "MockExamination"; char[] mockarray = {'m', 'o', 'c', 'k'; System.out.println(mock.length() / 2); System.out.println(mockArray.length / 2); System.out.println(mock.lastIndexOf('o')); if (mock.startswith("exam", 4)) System.out.println("YES"); else System.out.println("NO"); Arrays.sort(mockArray); System.out.println(mockArray[1]); Arrays.fill(mockArray, 'e'); for (char c: mockarray) System.out.print(c); System.out.println(); //end main //end class Question Four: [ marks] Write a Java method called endwithspercentage that takes an array of Strings called words as an argument. The method should calculate and print on the screen the percentage of the words that ends with the letter 's' in the array rounded to 3 decimal places. You could assume that all strings in the array are consists of lower-case letters. Example: Assume that the array includes the following Strings: pass, fail, marks The output should be: The percentage of words that ends with the letter 's' is: % Question Five: [ marks] Assume that there is a file called numbers.txt includes many integers, one integer per line. Write a Java application that reads the integers from the file and prints on the screen the maximum integer of them. You could assume that all integers in the file are positive. Example: Assume that the file contains the following integers: The output should be: The maximum integer in the file is: 15 Page 3 of 6

4 Question Six: [ marks] Given the following code for class PointIn2D: public class PointIn2D { private int x; private int y; public PointIn2D(int x, int y) { setx(x); sety(y); public void setx(int _x) { x = _x; public int getx() { return x; public void sety(int _y) { y = _y; public int gety() { return public String tostring() { return String.format("A point at:\nx:%d, y:%d",getx(), gety()); //end class a. In a single Java statement, declare a variable called point2d of type PointIn2D and let it refer to a point its x-coordinate is 3 and its y-coordinate is 4. b. What is the output after executing the following statement (assuming that you did part a correctly) System.out.println(point2d); c. Write the code of the class PointIn3D according to the following specifications: It is a subclass from the class PointIn2D. It has a new attribute represents the z-coordinate. It has a 3-argument constructor that takes 3 arguments to initialize the 3 attributes: x, y and z. It has an accessor method and a mutator method for the new attribute. It rewrites the code of tostring() method to include the new attribute. Hint: Use OOP style, like invoking the public methods instead of using the attributes directly and invoking the methods of the super class instead of rewriting the code. Page 4 of 6

5 Solution Question One: Question No. Answer 1 B 2 D 3 C 4 D 5 C 6 A 7 C 8 D 9 A 10 B Question Two: public static void stopatone(int max) { for (int i=max; i >= 1; i--) System.out.println(i); Question Three: a b YES k eeee Page 5 of 6

6 Question Four: public static void endwithspercentage(string[] words) { int count = 0; String w; char last; for (int i=0; i < words.length; i++) { w = words[i]; last = w.charat(w.length() - 1); if (last == 's') count++; // end for double percentage = (double) count / words.length * 100; System.out.printf("%s%.3f%%\n", "The percentage of words that ends with the letter 's' is: ", percentage); // end method Question Five: import java.util.scanner; import java.io.file; public class Q5M { public static void main(string[] args) throws Exception{ Scanner input = new Scanner(new File("numbers.txt")); int num; int max = 0; while (input.hasnext()) { num = input.nextint(); if (num > max) max = num; // end while System.out.println("The maximum integer in the file is: " + max); // end main //end class Question Six: a. PointIn2D point2d = new PointIn2D(3, 4); b. A point at: x:3, y:4 c. public public class PointIn3D extends PointIn2D { private int z; public PointIn3D(int x, int y, int z) { super(x, y); setz(z); public void setz(int _z) { z = _z; public int getz() { return z; public String tostring() { return super.tostring() + ", z:" + getz(); Page 6 of 6