Instruction to students:

Transcription

1 Benha University 2 nd Term (2012) Final Exam Class: 2 nd Year Students Subject: Object Oriented Programming Faculty of Computers & Informatics Date: 20/5/2012 Time: 3 hours Examiner: Dr. Essam Halim Instruction to students: 1. Language allowed to answer is the English language. 2. You should attempt 40 out of the 50 MCQ questions in Section I. 3. You should attempt all of Section II (Section II comprises questions 2, 3, and 4). 4. The exam paper is 14 pages long, and is in 2 sections. 5. The approximate allocation of marks is shown in brackets by the questions. 6. Section I contains multiple choice questions. Answer for the multiple choice questions should be written in the next table move it to the answer sheet. Section I : Key answer for the multiple choice questions Questions Questions Questions Questions Questions Page 1 of 15

2 Answer the following questions: Section I [Total 60] Q(1): Multiple choice questions Answer only 40 of the following 50 multiple choice questions, by selecting the correct answer in each. Place the answer on the special MCQ form. Each question [1.5 Mark] 1 If a number is too large to be stored in a variable of the float type, it. A. causes overflow B. causes underflow C. causes no error D. cannot happen in Java 2 What is i printed in the following code? int j = 0; int i = j++ + j * 5; System.out.println("What is i? " + i); A. 0 B. 1 C. 5 D. 6 3 Analyze the following code. import javax.swing.*; public class ShowErrors { int i; int j; String s = JOptionPane.showInputDialog(null, "Enter an integer", "Input", JOptionPane.QUESTION_MESSAGE); j = Integer.parseInt(s); i = (i + 4); A. The program cannot compile because j is not initialized. B. The program cannot compile because i does not have an initial value when it is used in i = i + 4; C. The program compiles but has a runtime error because i does not have an initial value when it is used in i = i + 4; D. The program compiles and runs fine. Page 2 of 15

3 4 Suppose x=10 and y=10 what is x after evaluating the expression (y >= 10) (x-- > 10). A. 9 B. 10 C What is y after the following statement is executed? x = 0; y = (x > 0)? 10 : -10; A. -10 B. 0 C. 10 D. 20 E. Illegal expression 6 How many times will the following code print "Welcome to Java"? int count = 0; do { System.out.println("Welcome to Java"); count++; while (count < 10); A. 8 B. 9 C. 10 D. 11 E. 0 7 Is the following loop correct? for (; ; ); A. Yes B. No 8 How many times is the println statement executed? for (int i = 0; i < 10; i++) for (int j = 0; j < i; j++) System.out.println(i * j) A. 100 B. 20 C. 10 D. 45 Page 3 of 15

4 9 What is sum after the following loop terminates? int sum = 0; int item = 0; do { item++; sum += item; if (sum >= 4) continue; while (item < 5); A. 15 B. 16 C. 17 D Will the following program terminate? int balance = 10; while (true) { if (balance < 9) continue; balance = balance - 9; A. Yes B. No 11 The signature of a method consists of. A. method name B. method name and parameter list C. return type, method name, and parameter list D. parameter list 12 Given the following method static void nprint(string message, int n) { while (n > 0) { System.out.print(message); n--; What is the printout of the call nprint('a', 4)? A. aaaaa B. aaaa C. aaa D. invalid call Page 4 of 15

5 13 The client can use a method without knowing how it is implemented. The details of the implementation are encapsulated in the method and hidden from the client who invokes the method. This is known as. A. information hiding B. encapsulation C. method hiding D. simplifying method 14 is to implement one method in the structure chart at a time from the top to the bottom. A. Bottom-up approach B. Top-down approach C. Bottom-up and top-down approach D. Stepwise refinement 15 Which of the following statements is valid? A. int i = new int(30); B. double d[] = new double[30]; C. int[] i = {3, 4, 3, 2; D. char[] c = new char(); E. char[] c = new char[4]{'a', 'b', 'c', 'd'; 16 Analyze the following code: final int[] x = {1, 2, 3, 4; int[] y = x; x = new int[2]; for (int i = 0; i < y.length; i++) System.out.print(y[i] + " "); A. The program displays B. The program displays 0 0 C. The program has a compile error on the statement x = new int[2], because x is final and cannot be changed. D. The elements in the array x cannot be changed, because x is final. 17 When you return an array from a method, the method returns. A. a copy of the array B. a copy of the first element C. the reference of the array D. the length of the array Page 5 of 15

6 18 Which of the following declarations are correct? A. public static void print(string strings, double numbers) B. public static void print(double numbers, String name) C. public static double print(double d1, double d2) D. public static void print(double numbers) E. public static void print(int n, double numbers) 19 What is the printout of the following program? int[][] values = {{3, 4, 5, 1, {33, 6, 1, 2; for (int row = 0; row < values.length; row++) { System.out.print(m(values[row]) + " "); public static int m(int[] list) { int v = list[0]; for (int i = 1; i < list.length; i++) if (v < list[i]) v = list[i]; return v; A B. 1 1 C. 5 6 D E Which of the following statements are true? A. Multiple constructors can be defined in a class. B. Constructors do not have a return type, not even void. C. Constructors must have the same name as the class itself. D. Constructors are invoked using the new operator when an object is created. 21 Variables that are shared by every instances of a class are. A. public variables B. private variables C. instance variables D. class variables Page 6 of 15

7 22 You should add the static keyword in the place of? in Line in the following code: 1 2 private int age; 3 4 public? int square(int n) { 5 return n * n; public? int getage() { 9 10 A. in line 4 B. in line 8 C. in both line 4 and line 8 D. none 23 Analyze the following code. int n = 2; xmethod(n); System.out.println("n is " + n); void xmethod(int n) { n++; A. The code has a compile error because xmethod does not return a value. B. The code has a compile error because xmethod is not declared static. C. The code prints n is 1. D. The code prints n is 2. E. The code prints n is Analyze the following code: private int t; int x; System.out.println(t); A. The variable t is not initialized and therefore causes errors. B. The variable t is private and therefore cannot be accessed in the main method. C. t is non-static and it cannot be referenced in a static context in the main method. D. The variable x is not initialized and therefore causes errors. E. The program compiles and runs fine. Page 7 of 15

8 25 What is the output of the following program? import java.util.date; Date date = new Date( ); m1(date); System.out.print(date.getTime() + " "); m2(date); System.out.println(date.getTime()); public static void m1(date date) { date = new Date( ); public static void m2(date date) { date.settime( ); A B C D What is the output of the following code? String s1 = "Welcome to Java!"; String s2 = "Welcome to Java!"; if (s1 == s2) System.out.println("s1 and s2 reference to the same String object"); else System.out.println("s1 and s2 reference to different String objects"); A. s1 and s2 reference to the same String object B. s1 and s2 reference to different String objects 27 What is the output of running class C? class A { public A() { System.out.println( "The default constructor of A is invoked"); class B extends A { public B() { System.out.println( "The default constructor of B is invoked"); public class C { B b = new B(); Page 8 of 15

9 A. Nothing displayed B. "The default constructor of B is invoked" C. "The default constructor of A is invoked""the default constructor of B is invoked" D. "The default constructor of B is invoked""the default constructor of A is invoked" E. "The default constructor of A is invoked" 28 Which of the statements regarding the super keyword is incorrect? A. You can use super to invoke a super class constructor. B. You can use super to invoke a super class method. C. You can use super.super.p to invoke a method in superclass's parent class. D. You cannot invoke a method in superclass's parent class. 29 Which of the following statements are true? A. A method can be overloaded in the same class. B. A method can be overridden in the same class. C. If a method overloads another method, these two methods must have the same signature. D. If a method overrides another method, these two methods must have the same signature. E. A method in a subclass can overload a method in the superclass. 30 What is the output of the following code? new Person().printPerson(); new Student().printPerson(); class Student extends Person { public String getinfo() { return "Student"; class Person { public String getinfo() { return "Person"; public void printperson() { System.out.println(getInfo()); A. Person Person B. Person Student C. Stduent Student D. Student Person 31 Which of the following statements is false? Page 9 of 15

10 A. A public class can be accessed by a class from a different package. B. A private method cannot be accessed by a class in a different package. C. A protected method can be accessed by a subclass in a different package. D. A method with no visibility modifier can be accessed by a class in a different package. 32 are referred to as heavyweight components. A. AWT components B. Swing components C. GUI components D. Non-GUI components 33 The correct order of the following three statements is. 1. frame.setlocationrelativeto(null); 2. frame.setsize(100, 200); 3. frame.setvisible(true); A B C D Suppose a JFrame uses the GridLayout(0, 2). If you add six buttons to the frame, how many columns are displayed? A. 1 B. 2 C. 3 D creates a color object. A. new Color(0, 0, 0) B. new Color(0, 266, 0) C. new Color(255, 255, 255) D. new Color(1, 2, 3) 36 To add a component c to a JPanel p, use. A. p.add(c) B. p.getcontentpane(c) C. p.insert(c) D. p.append(c) Page 10 of 15

11 37 Which of the following is not an advantage of Java exception handling? A. Java separates exception handling from normal processing tasks. B. Exception handling improves performance. C. Exception handling makes it possible for the caller's caller to handle the exception. D. Exception handling simplifies programming because the error-reporting and error-handling code can be placed at the catch block. 38 Which of the following statements are true? A. You use the keyword throws to declare exceptions in the method heading. B. A method may declare to throw multiple exceptions. C. To throw an exception, use the key word throw. D. If a checked exception occurs in a method, it must be either caught or declared to be thrown from the method. 39 An instance of describes the errors caused by your program and external circumstances. These errors can be caught and handled by your program. A. RuntimeException B. Exception C. Error D. Throwable E. NumberFormatException 40 Which of the following declares an abstract method in an abstract Java class? A. public abstract method(); B. public abstract void method(); C. public void abstract Method(); D. public void method() { E. public abstract void method() { 41 Which of the following statements regarding abstract methods are true? A. Abstract classes have constructors. B. A class that contains abstract methods must be abstract. C. It is possible to declare an abstract class that contains no abstract methods. D. An abstract method cannot be contained in a nonabstract class. E. A data field can be declared abstract. Page 11 of 15

12 42 Show the output of running the class Test in the following code lines: interface A { class C { class B extends D implements A { public class Test extends Thread { B b = new B(); if (b instanceof A) System.out.println("b is an instance of A"); if (b instanceof C) System.out.println("b is an instance of C"); class D extends C { A. Nothing. B. b is an instance of A. C. b is an instance of C. D. b is an instance of A followed by b is an instance of C. 43 Suppose a button jbt is placed in a frame, the coordinate of the button within the content pane of the frame is. A. (jbt.getx(), jbt.gety()) B. (jbt.x, jbt.y) C. cannot be obtained D. (0, 0) 44 You should override the method to draw things on a Swing component. A. repaint() B. update() C. paintcomponent() D. init() 45 Which of the following statements are true? A. You may create a Graphics object using new Graphics(). B. Whenever a GUI component is displayed, its Graphics object is automatically created. C. The paintcomponent method is automatically invoked by the JVM. You should never invoke it directly. D. Invoking repaint() causes paintcomponent to be invoked by the JVM. Page 12 of 15

13 46 Which of the following statements are correct? A. You can set an image on a label, but the image is not resizable. B. You can set an image on a button, but the image is not resizable. C. You can draw an image on a GUI component using the drawimage method in the Graphics object. This image is resizable. 47 Clicking the closing button on the upper-right corner of a frame generates a(n) event. A. ItemEvent B. WindowEvent C. MouseMotionEvent D. ComponentEvent E. ContainerEvent 48 Which of the following statements are true? A. Each event class has a corresponding listener interface. B. The listener object's class must implement the corresponding event-listener interface. C. A source may have multiple listeners. D. The listener object must be registered by the source object. 49 To get the x coordinate of the mouse pointer for the MouseEvent evt, you use. A. evt.getx() B. evt.getpoint().x C. Either A or B D. Neither A nor B 50 Analyze the following code: public class Test implements Runnable { Thread t = new Thread(this); t.start(); public void run() { System.out.println("test"); A. The program does not compile because this cannot be referenced in a static method. B. The program compiles fine, but it does not print anything because t does not invoke the run() method. C. The program compiles and runs fine and displays test on the console. D. None of the above. Page 13 of 15

14 Section II [Total 30] You should attempt all section II (questions 2, 3, and 4) Q(2): write a program that displays a message in a panel, and uses two buttons to move the message on the panel to the left or right as shown in Figure 1. [12 Marks] Q(3): (Creating four fans) Write a program that places four fans in a frame of GridLayout with two rows and two columns, as shown in Figure 2. [12 Marks] Figure 1 Figure 2 Q(4): Write a problem that prompts the user to enter a string and reports whether the string is a palindrome. Note that (palindrome if it reads the same forward and backward). [6 Marks] Page 14 of 15 Good Luck

15 Section I [Total 60] Q(1): Multiple choice questions Section I : Key answer for the multiple choice questions Questions Questions Questions Questions Questions Page 15 of 15