OLLSCOIL NA héireann THE NATIONAL UNIVERSITY OF IRELAND COLÁISTE NA hollscoile, CORCAIGH UNIVERSITY COLLEGE, CORK. Summer Examination 2012

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1 OLLSCOIL NA héireann THE NATIONAL UNIVERSITY OF IRELAND COLÁISTE NA hollscoile, CORCAIGH UNIVERSITY COLLEGE, CORK Summer Examination 2012 Computer Science CS5015 Object-oriented Software Development Prof. Ian Gent Prof. James A. Bowen Mr. Adrian P. O'Riordan Time: 3 Hours Answer all four questions Total = 140 marks Do not write answers on exam paper Page 1 of 8

2 Instructions for Question 1: There are a total of 50 marks for this multiple-choice question; each part is worth two marks. There is only one correct answer (a., b., c., or d.) for each question. Write all your answers in an answer book, such as (i) b., (ii) d., etc. Question 1. (i) The JDK command to compile a class Starter is a. java Starter b. java Starter.java c. javac Starter.java d. javac Starter (ii) When a variable s value may contain a fractional part you should assign the data type a. int b. double c. long int d. char (iii) What does it mean when a method returns the data type void? a. an empty memory space is returned that the program can utilize; b. method returns no value; c. void is not supported in Java; d. the return type is a reference to Object. (iv) What is the value of the res variable after this assignment? int res = * 5; a. 215 b. 108 c. 17 d. 25 (v) A class can have many methods with the same name as long as they differ in the number or type of parameters. This feature is called a. method invocation; b. method overloading; c. method overriding; d. method encapsulation. (vi) Consider the following code snippet. What will happen when the code is executed? String str = new String("Java"); char four = str.charat(4); a. throws a StringIndexOutofBoundsException; b. four is assigned value a ; c. four is assigned value null; d. throws an InputMismatchException. Page 2 of 8

3 (vii) Given the following piece of code: public interface Guard { void doyourjob(); public class Dog implements Guard { Which of the following statements is correct? a. code will not compile because doyourjob() in interface Guard must be abstract; b. code will not compile because Dog must implement doyourjob() from Guard; c. code will not compile because in Dog we must have extends instead of implements; d. code will compile without any errors. (viii) How many times will the following code print "Java Java"? int count = 1; while (count <= 10) { System.out.println("Java Java"); count++; a. zero times; b. eleven times; c. nine times; d. ten times. (ix) Which of the following statements about constructors are true? 1. A class can have zero, one or more user-defined constructors; 2. Constructors can have zero, one or more parameters; 3. The constructor must have the same name as the class and no return type. a. 1 and 2 only; b. 2 and 3 only; c. 1 and 3 only; d. 1, 2, and 3. (x) Consider the following lines of code: public class Rule{ public Rule(){ /*code not shown */ // more code here not shown... To successfully instantiate Rule, you can write... a. Rule rule42 = new Rule(); b. Rule rule42 = Rule(); c. Rule rule42 = Rule; d. Rule rule42 = rule; Page 3 of 8

4 (xi) What will be the result of compiling and running the following code fragment? try { int x = 0; int y = 5 / x; catch (Exception e) { System.out.println("Exception"); catch (ArithmeticException ae) { System.out.println("Arithmetic Exception"); System.out.println("Finished"); a. displays Finished on console output; b. does not compile; c. displays Exception on console output; d. displays Arithmetic Exception on console output. (xii) How many String instances will be eligible for garbage collection after the code snippet below is executed? String s1 = "s1"; String s2 = "s2"; String s3 = "s3"; s1 = s2; s2 = "new"; a. 1 b. 2 c. 0 d. 3 (xiii) What is the visibility of a field? a. the number of methods for which it is an input argument; b. the area of the program in which that variable name is defined; c. the length of time the variable name is active; d. a restriction on which other classes can access it directly; (xiv) What would be the output after running the following program? public class Dog { private String handle = "Skip"; public Dog(String handle) { this.handle = handle; public String gethandle() { return public String tostring() { return "Dog s name is " + handle; public static void main(string[] args) { System.out.println(new Dog("Spot")); Page 4 of 8

5 a. Spot b. Dog s name is Spot c. Skip d. Dog s name is Skip (xv) Which of the following is the correct statement to return the string JAVA? a. new touppercase("java"); b. "Java".toUpperCase(); c. Java.toUpperCase(); d. String.toUpperCase("Java"); (xvi) Java uses the keyword to reference the current object. a. Object b. super c. null d. this (xvii) Which one of these statements will legally declare, construct, and initialize an array? a. int [] myarr = {"1", "2", "3"; b. int [] myarr = new myarr{1, 2, 3; c. int [] myarr = new myarr{"1", "2", "3"; d. int [] myarr = {1, 2, 3; (xviii) Which one of the following statements about java.lang.exception is true? a. It is a final class; b. It extends Throwable; c. It is an abstract class; d. It implements Throwable. (xix) For the two classes Accommodation and Flat below, which one of the four statements in the possible answers will cause a compile error, if we assume flat is a reference to an object of the Flat class? public class Accommodation { protected int numrooms; private int monthlyrent; protected int getrent() { return monthlyrent; public class Flat extends Accommodation { public int floor; public int getfloor() { return floor; a. int level = flat.getfloor(); b. int rent = flat.getrent(); c. int rooms = flat.numrooms; d. int monthlyrent = flat.monthlyrent; Page 5 of 8

6 (xx) Which one of the following doesn t (directly or indirectly) invoke id s tostring() method? a. id.tostring() b. id.equals("abc123") c. "abc123" + id d. System.out.println(iD) (xxi) Assuming you have a Graphics object called page, which statement will draw an outline of a circle of diameter 30 and the upper-left corner at (20, 20)? a. page.drawoval(20, 20, 30, 30); b. page.drawoval(35, 35, 30, 30); c. page.drawcircle(20, 20, 30, 30); d. page.filloval(35, 35, 30, 30); (xii) Which method sets the font to Helvetica 20-point bold in the current component object? a. setfont(new Font("Helvetica", Font.BOLD, 20)); b. setfont(font("helvetica", Font.BOLD, 20)); c. Graphics.setFont(new Font("Helvetica", BOLD, 20)); d. page.setfont(font("helvetica", BOLD, 20)); (xxiii) Which of the following statements terminates the program when closing a JFrame called frame? a. frame.setdefaultcloseoperation(exit_on_close); b. frame.setdefaultcloseoperation(null); c. frame.setdefaultcloseoperation(); d. frame.setdefaultcloseoperation(jframe.exit_on_close); (xxiv) Which one of the following is not a top-level Swing container? a. javax.swing.jdialog b. javax.swing.jframe c. java.awt.container d. javax.swing.japplet (xxv) What is the default layout for JPanel? a. BorderLayout b. BoxLayout c. GridLayout d. FlowLayout Page 6 of 8

7 Question 2. (Total of 30 marks for this question) An abstract class Product represents an item for sale on-line. Products have a unique identifier assigned on creation. Two types of products, Ebook and Music, are for sale. Create an interface called Readable with the single method readit(). An implementation of readit() should display a simple message such as I m reading. Ebook should of course implement Readable. Provide zero-argument and one-argument constructors for Ebook and Music. The classes have a booktitle and songtitle field respectively. Override the tostring() method for each also. The use of inheritance and interfaces will gain higher marks. Marks will be given for good program design, code layout, and choice of identifiers as well as a satisfactory implementation of the requirements above. No marks will be given for comments, test code, or the inclusion of extra functionality not described above. Question 3. (Total of 30 marks for this question) Write a Java program to implement the GUI as shown below. When the user enters an integer into the input field (top left in illustration) and then clicks the Compute! button, the square root of the input number should appear in the result field (bottom). Concentrate on creating the components, adding them to a container and activating them. Use default colours and fonts. The screenshot is an example you do not have to replicate that exact layout or positioning default layout is sufficient. Marks will be given for good program design, code layout, and choice of identifiers as well as a satisfactory implementation of the requirements above. No marks will be given for comments or the inclusion of extra functionality not described above. Question 4. (Total of 30 marks for this question) (i) List six features commonly found in Java IDEs, such as Eclipse or DrJava, not available to programmers using a simple text editor (e.g. Notepad) and command line JDK. (3 marks) (ii) List two core features of the Java programming language that changed from Java version 2 to Java 5 and give a usage example for each. (4 marks) (iii) Explain the role played by packages in the Java platform. How does an API differ from a package? (4 marks) (iv) List three ways of deploying Java. Describe the basic operation of Java WebStart. (5 marks) (v) What is event-driven programming? Explain the role played by events in Java GUIs. (4 marks) Page 7 of 8

8 (vii) Explain what is meant by a layout manager in the context of Java GUIs. Explain the basic operation of two AWT/Swing layout managers you are familiar with. (5 marks) (viii) Outline a software development lifecycle with the aid of a diagram. Give a risk associated with your choice. (5 marks) Page 8 of 8