PROGRAMMING
COMPSCI 4039
Thursday 30 April 2020
1. For each of the following code snippets, write the output that the code would produce and describe why the output is as it is, paying particular attention to the looping criteria: how i is initialized, how and when it is changed, and how the loop terminates.
(a)
for(int i=0;i<5;i++) {
System.out.println(i);
} [1 mark]
(b)
for(int i=1;i<7;i*=2) {
System.out.println(i);
} [1 mark]
(c)
int i = 0;
while(i<3) {
System.out.println(i++);
} [1 mark]
(d)
int i = 3;
while(i<5) {
System.out.println(++i);
} [1 mark]
(e)
int i = 5;
do {
System.out.println(i);
i+=1;
}while(i<4); [1 mark]
2. Examine the following class and answer the questions below:
1. public class Mystery {
2. public static int c = 0;
3. public static void main(String[] args) {
4. int[] a = {8,1,-3,12,4};
5. System.out.println(go(a,0,a.length));
6. } 7.
8. public static int go(int[] a,int le,int ri) {
9. c += 1;
10. if(ri - le <= 1) {
11. return a[le];
12. }
13. else {
14. int cp = le+(ri-le)/2;
15. int m1 = go(a,le,cp);
16. int m2 = go(a,cp,ri);
17. if(m1 > m2){
18. return m1;
19. }else {
20. return m2;
21. }
22. }
23. }
24. }
(a) The main method passes an array of type int to the method go. From examining the code, deduce what useful property ofthe array the method go returns. [1 mark]
(b) This program makes use of a particular programming style. described in the course (see e.g. line 15). What is it? [1 mark]
(c) Describe how the program achieves its goal. In particular, step through the different calls to the go method, in the order in which they happen, and what the method returns. You do not need togo through all the calls (there will be 9 in this example), just enough to be able to describe how the program works. [6 marks]
(d) If the input array was changed to {1,4,10,3,10} which position in the array would the value returned by the first call to go (line 5) correspond to? Justify your answer. The first position is position zero. [3 marks]
(e) The program currently only works with int arrays. Describe any modifications you would make to the original code that would allow it to work with any type for which is possible to compare two elements. [4 marks]
3. Study the following class and then answer the questions below.
1. public class ExamQ3 {
2. private int a;
3. public ExamQ2(int b) {
4. a = b;
5. }
6. private int getA() {
7. return a;
8. }
9. private void setA(int b) {
10. a = b;
11. }
12. public String toString() {
13. return "" + a;
14. }
15. public static void add3(int a) {
16. a += 3;
17. }
18. public static void add3Obj(ExamQ2 e) {
19. e.setA(3 + e.getA());
20. }
21. public static void main(String[] args) {
22. int a = 5;
23. ExamQ2 ee = new ExamQ2(a);
24. add3(a);
25. System.out.println(a);
26. add3Obj(ee);
27. System.out.println(ee.getA());
28. }
29. }
(a) What is the meaning of private online 2? [1 mark]
(b) Line 9 contains a method signature. Copy the signature, and label each of its components, describing their meaning. [2 marks]
(c) Overriding, overloading, interfaces, superclasses and subclasses are all concepts and phenomena that we use when building object oriented programs. One is used in this example. State which one, and on which line. [1 mark]
(d) Describe all of the things being created on line 23. [2 marks]
(e) The four lines starting from line 24 contain two calls to methods that add 3 to an integer. State the outputs at lines 25 and 27. Describe in detail why you believe the outputs are as you have stated. [4 marks]
4. A local school awards pupils with points for performing good deeds in the class (tidying up, helping others, etc). At the end of each week, the pupil with the highest number of points wins a prize. You are part of a team that has been asked by the school to help them write a program to keep track of the points each week and why they were awarded. The program stores the current points in a text file, in which each line corresponds to one instance of a pupil having been awarded points (i.e. each pupil may appear in multiple lines):
(and the fields are separated by spaces). When the program is run, it first loads this file, storing the data, and then waits for the user to type an input. There are three types of input:
The user can add points to a student by typing:
ADD
(again, fields separated by spaces). You can assume that will never include any spaces, both here and in the original file.
The user can reset all pupils to having no points with: RESET
Or list all pupils in descending order of total points with: LIST
(a) The team decides to solve this problem with a solution that includes a class Pupil, objects of which will represent each pupil and a class AwardedPoints that will represent a particular instance of points being awarded to a student. The Pupil class should store references to all instances of points awarded to that pupil. Provide code for a suitable AwardedPoints class. Justify all attributes and methods you include based on the problem description above. It should be possible to make an object with or without a String argument representing . You do not need to include import statements in any code in this question. Use only Java classes we covered in the course. [3 marks]
(b) Provide code for a suitable Pupil class. Justify any methods you include based on the problem description above. You can assume that any particular Pupil will never be awarded points more than 100 times. [6 marks]
(c) Two Pupil objects will be defined as equal if they share the same first and second
names. Write a .equals(Object o) method for your class that meets this specification. You can assume throughout that two different pupils never share both a first and second name. [3 marks]
(d) It is decided to implement the ADD command by creating a new temporary Pupil object with the data entered by the user in the ADD command. This temporary Pupil object will then be compared against all pupils in the array to find a match using the .equals method (from part (d)). Write a method that takes as its arguments the Pupil array, a reference to an individual Pupil object and to an AwardedPoints object. The method should find the entry in the array that matches the individual Pupil object and add the AwardedPoints object to the pupil. If the pupil does not exist in the array, it should be added to the array. [4 marks]
(e) Write code to read the data file and store the results into an array of Pupil objects. You do not need to include exception handling and you can assume that the data file is always correctly formatted. The first line of the file corresponds to the first pupil (i.e. there are no headers in the file). You can assume there will never be more than 100 pupils. [4 marks]
(f) Assume that another team member has provided a compareTo method allowing you to use Arrays.sort to sort your Pupil array so that the highest scoring pupil is in the first position. Write code that will prompt the user for input, parse the input, decide upon the relevant action and then perform that action. You can assume that the user always enters the data correctly. [4 marks]
(g) Other team members are programmers but are not experienced in object oriented (OO) programming. Describe to them four benefits of an OO approach for this application. Be as specific as possible, ensuring that you make reference to features of this particular program. As they are programmers, you can assume that they are familiar with concepts like variables and methods. Each benefit should require no more than one or two sentences. [4 marks]
(h) Within the team, before development you discussed two possible solutions. One that consisted of just a Pupil class and the one that was ultimately chosen consisting of separate classes to represent Pupils and AwardedPoints. Describe why the second option is better. Ensure your answer is specific to this application, and not an argument for object orientation in general. [2 marks]