THE UNIVERSITY OF AUCKLAND

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1 VERSION COMPSCI 230 THE UNIVERSITY OF AUCKLAND SECOND SEMESTER, 2011 Campus: City Computer Science TEST Software Design and Construction (Time Allowed: 50 MINUTES) Note: The use of calculators is NOT permitted. Compare the test version number on the Teleform sheet supplied with the version number above. If they do not match, ask the supervisor for a new sheet. Enter your name and student ID on the Teleform sheet. Your name should be entered left aligned. If your name is longer than the number of boxes provided, truncate it. Answer Section A of Multiple-choice questions on the Teleform answer sheet provided. Answer Section B in the space provided in this booklet. Attempt all questions. Use a dark pencil to mark your answers in the multiple choice answer boxes on the Teleform sheet. Check that the question number on the sheet corresponds to the question number in this question/answer book. If you spoil your sheet, ask the supervisor for a replacement. Write your answers in the space provided in the short answer section. Write as clearly as possible. The space provided will generally be sufficient but is not necessarily an indication of the expected length. Extra space is provided at the end of this test booklet. An appendix with a simplified API is included on the last page. You may detach this appendix. Surname: First Name(s): Student ID: Login Name(UPI): MARKERS ONLY Section Marks Of A 26 B 24 Total 50

2 VERSION COMPSCI 230 SECTION A MULTIPLE CHOICE QUESTIONS For each question, choose the best answer according to the information presented in lectures. Select your preferred alternative on the Teleform answer sheet provided. The following FIVE questions relate to the classes given below: class A { int x; A() { this(100); A(int x) { this.x = x; public String tostring() { return "A:" + x; class B extends A { int x = 10; int y = x+1; B() { B(int y) { this.y = this.y + y; B(int x, int y) { super(x); this.y = this.y + y; public String tostring() { return "A:" + super.x + ", B:(" + x + "," + y + ")"; Question 1 [1 mark] What will be printed after executing the following code fragment? A a1 = new A(); System.out.println(a1); (a) A:0 (b) A:100 (c) B:1 (d) B:100 (e) A:1

3 VERSION COMPSCI 230 Question 2 [1 mark] What will be printed after executing the following code fragment? A a2 = new A(10); System.out.println(a2); (a) A:10 (b) A:0 (c) B:100 (d) B:10 (e) A:100 Question 3 [2 marks] What will be printed after executing the following code fragment? B b1 = new B(); System.out.println(b1); (a) A:100, B:(100,101) (b) A:10, B:(100,101) (c) A:10, B:(10,11) (d) A:100, B:(10,11) (e) None of the above Question 4 [2 marks] What will be printed after executing the following code fragment? B b2 = new B(20); System.out.println(b2); (a) A:100, B:(10,131) (b) A:100, B:(100,121) (c) A:100, B:(10,31) (d) A:20, B:(10,31) (e) A:0, B:(10,1) Question 5 [2 marks] What will be printed after executing the following code fragment? B b3 = new B(20, 50); System.out.println(b3); (a) A:20, B:(20,71) (b) A:100, B:(10,61) (c) A:20, B:(10,61) (d) A:100, B:(100,151) (e) A:0, B:(20,51)

4 VERSION COMPSCI 230 The following FOUR questions relate to the classes given below: class A1 { int x=10; public void method() { System.out.print("A:" + this.x + " "); class B1 extends A1 { int x=20; public void method() { System.out.print("B:" + this.x + " "); public static void main(string args[]) { A1 p = new A1(); B1 q = new B1(); //... Question 6 [1 mark] What will be printed after executing the following code fragment? p.method(); q.method(); (a) A:0 B:0 (b) A:10 B:20 (c) A:20 B:20 (d) A:10 B:10 (e) A:20 B:10 Question 7 [1 mark] What will be printed after executing the following code fragment? A1 s = new B1(); s.method(); (a) B:20 (b) A:10 (c) A:20 (d) A:10 B:20 (e) B:10 Question 8 [2 marks] What will be printed after executing the following code fragment? System.out.print(((A1)q).x); System.out.print(((B1)q).x); (a) 1020 (b) 2010 (c) 2020 (d) 1010 (e) None of the above

5 VERSION COMPSCI 230 Question 9 [2 marks] What is the result of attempting to compile and run the following statement? ((A1)q).method(); ((B1)q).method(); (a) B:20 B:20 (b) A:10 B:20 (c) A:20 B:10 (d) A:10 B:10 (e) None of the above Question 10 [1.5 marks] Declaring a method final means: (a) it will prepare the object for garbage collection. (b) it cannot be overridden. (c) it cannot be overloaded. (d) it cannot be accessed from outside its class. (e) None of the above Question 11 [1.5 marks] Assigning a subclass reference to a superclass variable is safe: (a) only when the superclass is concrete. (b) only when the superclass is abstract. (c) because the subclass object is an object of its superclass. (d) because the subclass object has an object of its superclass. (e) None of the above Question 12 [1 mark] The default equals implementation of the Object class determines: (a) whether two references have the same type. (b) whether two objects have the same instance variables. (c) whether two objects have the same instance variable values. (d) whether two references refer to the same object in memory. (e) None of the above. Question 13 [1.5 marks] A class that implements an interface but only gives definitions for some of the method headings given in the interface is called a/an: (a) friendly class (b) abstract class (c) concrete class (d) discrete class (e) None of the above.

6 VERSION COMPSCI 230 Question 14 [1.5 marks] Which of the following statements about interfaces is FALSE? (a) An interface describes a set of methods that can be called on an object, not providing concrete implementation for the methods. (b) Once a class implements an interface, all objects of that class have an is-a relationship with the interface type. (c) An interface describes a set of methods that can be called on an object, providing a default implementation for the methods. (d) Interfaces are useful when attempting to assign common functionality to possibly unrelated classes. (e) None of the above Question 15 [1 mark] Which of the following statements is FALSE? (a) Parameterized type ArrayList< Number > is a supertype of ArrayList< Integer >. (b) A wildcard represents an unknown type. (c) ArrayList implements a dynamically resizable, array-like data structure. (d) Because the wildcard in a method s header does not specify a type parameter name, you cannot use it as a type name throughout the method s body. (e) None of the above The following FOUR questions relate to the classes given below: class Car implements Cloneable { private String licenseplate; // e.g. "ABC123" private double maxspeed; // in kilometers per hour public Car(String lp, double max) { licenseplate = lp; maxspeed = max; public static void main(string[] args) throws Exception{ Car c1 = new Car("ABC123", 150.0); Car c2 = new Car("ABC123", 150.0); Car c3 = (Car) c1.clone(); ArrayList<Car> carlist1 = new ArrayList<Car>(); carlist1.add(c1); carlist1.add(c2); ArrayList carlist2 = (ArrayList) carlist1.clone();

7 VERSION COMPSCI 230 Question 16 [1 mark] What will be printed after executing the following code fragment? (Hint: What is the default implementation of the Object.equals() method?) System.out.print(c1 == c2); System.out.print(" "); System.out.print(c1.equals(c2)); (a) false true (b) false false (c) true false (d) true true (e) None of the above. Question 17 [1 mark] What will be printed after executing the following code fragment? System.out.print(c1 == c3); System.out.print(" "); System.out.print(c1.equals(c3)); (a) false true (b) true false (c) true true (d) false false (e) None of the above. Question 18 [1 mark] What will be printed after executing the following code fragment? System.out.print(carList1==carList2); System.out.print(" "); System.out.print(carList1.equals(carList2)); (a) false false (b) true false (c) false true (d) true true (e) None of the above. Question 19 [1 mark] What will be printed after executing the following code fragment? System.out.print(carList1.get(0).equals(carList2.get(0))); System.out.print(" "); System.out.print(carList1.get(0)==carList2.get(0)); (a) true false (b) false false (c) true true (d) false true (e) None of the above.

8 VERSION COMPSCI 230 Question/Answer Sheet ID. SECTION B Answer all questions in this section in the space provided. If you run out of space then please use the Overflow Sheet and indicate in the allotted space that you have used the Overflow Sheet. Question 20: Assignment 1 [16 marks] In assignment 1, you were asked to add several changes to the program which displays moving shapes bouncing off the edges of the window. (a) Complete the MovingSpecialShape class which draws a special square on the animation panel. The square is filled with the fill colour and the border is drawn with the border colour. It also has a red circle which rotates around the circular boundary. Some examples are given below: (p.x, p.y) radius * Math.cos(radian) (cx, cy) radius * Math.sin(radian) radius You are required to calculate the top left corner (rx, ry) of the red circle. The position of the red circle depends on the angle rotated referenced by the centre point (cx, cy) of the shape. The radius of the shape depends on the width/height of the shape. Given the following classes: (rx, ry) import java.awt.*; public abstract class MovingShape { public int marginwidth, marginheight; protected Point p; protected int width, height; protected Color fillcolor; protected MovingPath path; protected 8oolean selected = false; protected Color bordercolor; // the margin of the animation // the top left corner of the shapes // the width and height of the shapes // the fill colour of the shapes // the moving path of the shapes // draw handles if selected // the border colour of the shapes public MovingShape() { this(0, 0, 20, 20, 500, 500, Color.blue, Color.black, 0);

9 VERSION COMPSCI 230 Question/Answer Sheet ID. public MovingShape(int x, int y, int w, int h, int mw, int mh, Color fc, Color bc,int pathtype) { p = new Point(x,y); marginwidth = mw; marginheight = mh; fillcolor = fc; bordercolor = bc; width = w; height = h; setpath (pathtype); public abstract boolean contains(point p); public abstract void draw(graphics g); import java.awt.*; public class MovingRectangle extends MovingShape { public MovingRectangle() { super(); public MovingRectangle(int x, int y, int w, int h, int mw, int mh, Color fc, Color bc, int typeofpath) { super(x,y,w,h,mw,mh,fc,bc, typeofpath); public void draw(graphics g) { Graphics2D g2d = (Graphics2D) g; g.setcolor(fillcolor); g.fillrect(p.x, p.y, width, height); g.setcolor(bordercolor); g.drawrect(p.x, p.y, width, height); drawhandles(g); public boolean contains(point mousept) { return (p.x <= mousept.x && mousept.x <= (p.x + width + 1) && p.y <= mousept.y && mousept.y <= (p.y + height + 1)); import java.awt.*; public class MovingSquare extends MovingRectangle { public MovingSquare() { super(); public MovingSquare(int x, int y, int s, int mw, int mh, Color fc, Color bc, int typeofpath) { super(x,y,s,s,mw,mh,fc,bc, typeofpath); public void setwidth(int w) { super.setwidth(w); super.setheight(w); public void setheight(int h) { super.setwidth(h); super.setheight(h);

10 VERSION COMPSCI 230 Question/Answer Sheet ID. Complete the class MovingSpecialShape below. Do not duplicate code unnecessarily. public class MovingSpecialShape extends { int angle; //2 marks public MovingSpecialShape() { super(); public MovingSpecialShape(int x, int y, int s, int mw, int mh, Color fc, Color bc, int typeofpath) { //2 marks public void { //1 mark super.draw(g); int centerx, centery, x1, y1; int radius = Math.min(width, height)/2 5; double radian = Math.PI * angle/180; //calculate the centre point (cx,cy) //2 marks //calculate the reference point (rx,ry) int dx = (int) (radius * Math.cos(radian)); int dy = (int) (radius * Math.sin(radian)); //2 marks g.setcolor(color.red); g.filloval(x1, y1, 10, 10); //update the angle //1 mark (10 marks)

11 VERSION COMPSCI 230 Question/Answer Sheet ID. (b) Rewrite the FallingPath class using an Anonymous Class public void setpath(int pathid) { switch (pathid) { case MovingPath.ROTATING : { path = new RotatingPath(); break; case MovingPath.FALLING : { path = new FallingPath(); break; public class FallingPath extends MovingPath { private double am = Math.random() * 20, stx =0.5, sindeltax = 0; public FallingPath() { public void move() { sindeltax = sindeltax + stx; p.x = (int) Math.round(p.x + am * Math.sin(sinDeltax)); p.y = p.y + deltay; if (p.y > marginheight) // if it reaches the bottom, restart p.y = 0; public void setpath(int pathid) { switch (pathid) { case MovingPath.ROTATING : { path = new RotatingPath(); break; case MovingPath.FALLING : { path = new { private double ; break; (6 marks)

12 VERSION COMPSCI 230 Question/Answer Sheet ID. Question 21: Generic Methods [8 marks] We would like to write a method which merges two collections/lists of the same type together. Example 1: Merging two integer lists: List<Integer> intlist1 = new ArrayList<Integer>(); intlist1.add(new Integer(1)); intlist1.add(new Integer(2)); System.out.println(intList1); List<Integer> intlist2 = new ArrayList<Integer>(); intlist2.add(new Integer(3)); System.out.println(intList2); merge(intlist1, intlist2); System.out.println(intList1); Output: [1, 2] [3] [1, 2, 3] Example 2: Merging two double lists: List<Double> doublelist1 = new ArrayList<Double>(); doublelist1.add(new Double(1.2)); doublelist1.add(new Double(2.3)); System.out.println(doubleList1); List<Double> doublelist2 = new ArrayList<Double>(); doublelist2.add(new Double(3.4)); System.out.println(doubleList2); merge(doublelist1, doublelist2); System.out.println(doubleList1); Output: [1.2, 2.3] [3.4] [1.2, 2.3, 3.4] Example 3: Merging two String lists: List<String> strlist1 = new ArrayList<String>(); strlist1.add( a ); System.out.println(strList1); List<String> strlist2 = new ArrayList<String>(); strlist1.add( b ); merge(strlist1, strlist2); System.out.println(strList1); [a] [a, b] Here s the first attempt: public static void merge(list<?> c1, List<?> c2) { for (Object o : c2) c1.add(o); However, the above method couldn t be compiled because you cannot just shove objects into a collection of unknown type.

13 VERSION COMPSCI 230 Question/Answer Sheet ID. (a) Rewrite the above method using generic methods. Method declarations can be parameterized by one or more type parameters. public static void merge(, ) { for ( ) c1.add(o); (6 marks) (b) Next, we would like to apply the merge method ONLY on the subclasses of the class Number. public abstract class Number extends Object public final class Integer extends Number public final class Double extends Number public final class Long extends Number Therefore, if you merge two String lists, your program will return a compile time error. List<String> strlist1 = new ArrayList<String>(); merge(strlist1, strlist2); >javac TestMyList.java TestMyList.java:38: <T>merge(java.util.List<T>,java.util.List<T>) in TestMyList cannot be applied to (java.util.list<java.lang.string>,java.util.list<java.lang.string>) merge(strlist1, strlist2); ^ 1 error Complete the new version of the merge method below. public static < > void merge(,... ) { (2 marks)

14 VERSION COMPSCI 230 Question/Answer Sheet ID. Overflow pages please number answers carefully

15 VERSION COMPSCI 230 Question/Answer Sheet ID. Overflow pages please number answers carefully APPENDIX FOLLOWS

16 APPENDIX COMPSCI 230 java.awt class Graphics void setcolor(color) void drawline(int, int, int, int) void drawoval(int, int, int, int) void drawpolygon(int[], int[], int) void drawpolygon(polygon) void drawrect(int, int, int, int) void filloval(int, int, int, int) void fillpolygon(int[], int[], int) void fillpolygon(polygon) void fillrect(int, int, int, int) Class Graphics2D void fill(shape s) void draw(shape s) class Polygon Polygon(int[] xpoints, int[] ypoints, int npoints) boolean contains(point p) boolean contains(int x, int y) Class ArrayList<E> boolean add(e o) void add(int index, E element) APPENDIX