CSCI 212 Practice Final Exam Summer Instructor: Krishna Mahavadi

Transcription

1 QUEENS COLLEGE Department of Computer Science CSCI 212 Practice Final Exam Summer Instructor: Krishna Mahavadi August 13, 2017

2 Problem 1 (10 points) (a): Create an interface MessageEncoder. It should have a single abstract method encode(plaintext), where plaintext is the message to be encoded. The method will return an encoded message. (b): Create a class SubstitutionCipher that implements the interface MessageEncoder, as described in part(a). The constructor should have one parameter, shift. Define a method encode so that each letter is shifted by the value in shift. For Example, if shift is 4, a will be replaced by e, b will be replaced by f, c will be replaced by g and so on.

3 Problem 2 (6 points) Each of the following 3 pieces of code might contain an error. For each part, if there is an error correct it by rewriting just the part of the code with a mistake in the space provided. If the code has no error, write No Error. (a): Due to a flaw in the following method, it will not compile. Identify the flaw and make approriate correction so that method will compile. public void displayabsx(int x){ if(x<0){ System.out.println(x); return; else{ System.out.println(-x); return; System.out.println("Done!"); (b): public class ClassA { public ClassA() { public final int method1(int x){ public double method2(int y) { public class ClassB extends ClassA { public ClassB() { public int method1 (int y) { public double method2 (double z) { (c): The following method hasduplicatevalues() shown below is supposed to return t rue if the array contains any repeated integers and return f alse if all integers in the array are unique. public boolean hasduplicatevalues(int[] data) { for(int i = 0; i< data.length; i++) for(int j=0; i < data.length; j++) if (data[i] == data[j]) return true; return false;

4 Problem 3 (10 points) Assume that you are given class SchoolKid. It has instance variables name, age, teachername, and greeting. The class has all the appropriate methods for each of the attributes and constructors. Write a derived class ExaggeratingKid that extends the class SchoolKid. The new class has no new instance variables. However, you should have a constructor for the four attributes, and it should override the accessor method for the age, reporting the actual age plus 2. It also should override the accessor method for the greeting, returning the child s greeting concatenated with the words I am the best. Finally write a tostring method. Note: Please do not write any of SchoolKid class constructors or methods. (a) Write constructor for the ExaggeratingKid class. (b): Override the accessor methods for age and greeting of SchoolKid class. (c): Override the SchoolKid class s tostring method.

5 Problem 4 (8 points) What will be printed by this program? public class X { private int a; public X(int i) {a =i; public void seta(int i) { a = i; public int geta() {return a; public class Y extends X{ private int b; public(int i, int j){ super(j); b = i; public void setb(int i) { b = i; public int getb() { return b; public class SupSubR { public static void main (String[] args){ X x = new X(10); X x2; Y y = new Y(5, 6); x2 = x; System.out.println("x2.getA(): " + x2.geta()); // (A) x2 = y; System.out.println("x2.getA(): " + x2.geta()); // (B) System.out.println(x2); // (C) System.out.println(y); // (D) System.out.println("x2.getB(): " + x2.getb()); // (E) Y y2 = new X(5); System.out.println(y2); (F) (a) Output generated at line A is: (b) Output generated at line B is: (c) Output generated at line C is: (d) Output generated at line D is: (e) Output generated at line E is: (f) Output generated at line F is:

6 Problem 5 (15 points) Write static methods for the class P5 that carry out the indicated tasks in this program. (a): There are n people in a room, where n is an integer greater than or equal to 2. Each person shakes hands once with every other person. What is the total number of handshaakes in the room? Write a recursive method to solve this problem with the following header: public static int handshake(int n) where handshake(n) returns the total number of handshakes for n people in the room. handshake(1) = 0; and handshake(2) = 1; To get you started, (b) Write a static method removeduplicates(arraylist<character> data) that will remove any duplicates of characters in the object data.always keep the first copy of a character and remove subsequent ones. (c): Create a window that extends JFrame. Add a Label using JLabel and a text field to enter data. Add to the window a button to convert Fahrenheit to celsius degrees. Do not add any action listeners.