PART1: Choose the correct answer and write it on the answer sheet:

Transcription

1 PART1: Choose the correct answer and write it on the answer sheet: (15 marks 20 minutes) 1. Which of the following is included in Java SDK? a. Java interpreter c. Java disassembler b. Java debugger d. All of the above 2. Give the value of the following expression or indicate if there is an error: 4 % 2 + 5/0: a. 2 c. 5 b. 0 d. Run-time error 3. Which of the following can beused to invoke a constructor of a class named Robot from within this class? a. Robot(1) c. this.set(1) b. this(1) d. this.get(1) 4. Which of the following techniques is used when the potential error is predictable and localized? a. Exception handling c. Defensive programming b. Exception declaration d. None of the above 5. Which of the following cannot be included in a Java interface? a. reference variables c. abstract methods b. constants d. All of the above 6. Which of the following methods is used for drawing on a JFrame? a. paint() c. decorate() b. draw() d. All of the above 7. Consider event driven programming in Java. Which of the following should be used when the programmer wants to respond to a small number of events? a. An event listener c. An adapter class b. An event source d. An inner class 8. Which of the following is a Java method that causes a Java thread to enter the blocked state? a. sleep c. yield b. run d. blocked 9. Which of the following is a Java mechanism that allows programs to transfer data between programs across the internet? a. socket c. webpage b. IP address d. web address 10. Which of the following HttpServlet methods passes HTTP requests to helper methods within a Servlet object? a. init c. destroy b. dooptions d. service

2 Part 2: Essay questions (30 marks 50 minutes) 1. What do the following terms refer to: J2SE, J2EE, and J2ME? (4 marks) These are Java editions: (1 mark) - Java 2 Standard Edition (J2SE) (1 mark) - Java 2 Enterprise Edition (J2EE) (1 mark) - Java 2 Micro Edition (J2ME) (1 mark) 2. What is a static variable in Java? Give an example of a static variable declaration. (4 marks) When you declare a static variable in a class, you are specifying that there is exactly one copy of the variable for all objects defined by that class. (2 marks) Example: (2 marks) public static final PI = 3.14; 3. When writing a method, you must deal with checked exceptions in one of two ways. What are these two ways? (6 marks) 1- Catch the exception and deal with it within the method, using a try-catch statement (Handling exceptions). (3 marks) 2- Declare in the method header that an exception may be thrown. In this case you do not handle the exception within the method, but simply pass it on to the calling method. (3 marks) 4. Briefly explain the meaning of a generic class in java. Give an example. (4 marks) A generic class is the one that has at least one member of an unspecified type. A programmer must then specify the desired type when creating an instance of the class. For example: (2 marks) ArrayList<String> mylist = new ArrayList<String>(10) (2 marks) 5. Answer the following: (6 marks) (a) What are the two ways of defining a threaded class in Java? (b) When is it preferred to use each of the above two ways? (a) 3 marks Threaded classes can be defined in two ways: method1- by inheriting from the Thread class: method2- by implementing the Runnable interface: (b) 3 marks method1 is used if you wish to inherit from only one class, the Thread class. method2 is used when you want to inherit from a class other than or as well as the Thread class. Another answer: If only the run() method is to be overridden then Runnable interface should be used. Subclassing of Thread is preferable if more than one method of the thread class is to be overridden or used. 6. List two differences between a Java applet and a Java application in terms of how the bytecode is invoked and executed. (6 marks) Java application: (3 marks) o Java application is typically installed directly on a particular computer and run there. o When an application is run, the bytecode is interpreted and executed by the Java Virtual Machine(JVM) on the computer where the application resides. Java applet (3 marks) o The bytecode for an applet is normally run when an associated web page is loaded into a browser. o The applet bytecode is actually interpreted and executed by Java-enabled browser or the appletviewer. M257 Final - Form A 2/5

3 Part 3: Problem Solving: (55 marks 110 minutes) 1. Develop a Java program that includes the following: (16 marks) (a) An interface ShipmentInterface that includes a method: public double getshippingprice(). When this method is implemented in any class, it should return the total shipping price of a shipment according to the formula: shipping price = shipment weight X shipping rate (b) A public class Shipment that: - implements ShipmentInterface. - has two private instance variables, String id and double weight. - has a two-argument constructor that sets id and weight to given values. - overrides the Object s tostring() method in order to return a string consisting of a shipment id and weight; for example, ID: 10, Weight= 5. - implements any additional required methods. (c) A public class SpecialShipment that: - extends the Shipment class. - has a private instance variable, String contents - has a three-argument constructor that sets the value of id, weight, and contents to given values. You should invoke the superclass two-argument constructor for setting id and weight. 14 marks for all statements (as distributed below) (a) public interface ShipmentInterface { (1 mark) public double getshippingprice(double shippingrate); (1 mark) (b) public class Shipment implements ShipmentInterface{ (1 mark) private String id; (1 mark for all declaration) private double weight; public Shipment(String i, double w) { (2 marks) id = i; weight = w; public double getshippingprice(double shippingrate){ (1 mark) return weight*shippingrate; (1 mark) public String tostring(){(2 marks) return "ID: " + id + ", Weight: " + weight; (c) public class SpecialShipment extends Shipment{ (1 mark) private String contents; (0.5 mark) public SpecialShipment(String i, double w, String c) { (1 mark) super(i, w); (1 mark) contents = c; (0.5 mark) M257 Final - Form A 3/5

4 2. Write Java code that reads two real numbers from the user as two separate inputs, and displays the sum and average of these numbers. You don t need to write import statements. (7 marks) 6 marks for all statements (as distributed below) + 1 mark for overall logical flow and structure of the program double n1, n2; (0.5 mark) Scanner in = new Scanner(System.in); (1 mark) System.out.println("enter the first number"); (0.5 mark) n1 = in.nextint();(0.5 mark) System.out.println("enter the second number"); (0.5 mark) n2 = in.nextint();(0.5 mark) System.out.println("The sum is " + (n1+n2)); (1 mark) System.out.println("The average is " + (n1+n2)/2); (1 mark) In.close();(0.5 mark) Note to tutors: of course several other java classes could be used for input, e.g. BufferedReader and JOptionPane. 3. Consider the following code skeleton: (20 marks) public class MyFrame extends JFrame{ private JTextField txtdata, txtfile; private JLabel lbldata, lblfile; private JButton btnsave; public MyFrame() { //(1) private class myhandler implements ActionListener{ public void actionperformed(actionevent e) { try { //(2) catch (Exception ex) { JOptionPane.showMessageDialog(null, "Error!"); public static void main(string[] args) { new MyFrame().setVisible(true); (a) Write Java code at location (1) so that the following window appears when the main method is invoked. M257 Final - Form A 4/5

5 The above window includes two JLabel objects, two JTextField objects, and one JButton. The window s title is my program, and size is 250x100. The layout manager is GridLayout. And when the window s X button is pressed, the program terminates. (b) Write Java code at locations (1) and (2) so that when the Save button is clicked the data written in the top textbox is saved in a file with the name written in the bottom textbox; use PrintWriter class for that. When the saving operation is finished, the user should be notified; use JOptionPane class here. (c) What is the output if the file in which the data will be saved could not be created? 18 marks for (a) and (b) 16 marks for all statements (as distributed below) (a) At (1) setsize(250,100); (1 mark) settitle("my program"); (1 mark) setdefaultcloseoperation(exit_on_close); (1 mark) setlayout(new GridLayout(3, 2)); (1 mark) lbldata = new JLabel("Data:"); (3 marks for creating all instances) lblfile = new JLabel("Filename: c:\\"); txtdata = new JTextField(); txtfile = new JTextField(); btnsave = new JButton("Save"); add(lbldata);add(txtdata); (2 marks correct addition and order ) add(lblfile);add(txtfile); add(btnsave); (b) At (1) btnsave.addactionlistener(new myhandler());(2 marks) At (2) PrintWriter out = new PrintWriter("c:/1/" + txtfile.gettext()+ ".txt"); (1.5 marks) out.println(txtdata.gettext());(1.5 marks) out.close();(1 mark) JOptionPane.showMessageDialog(null, "Done!"); (1 mark) (c) 2 marks for (c) A JOptionPane window is shown with a message Error! 4. Write Java code to access a website, and display the first html line of its homepage. In your answer, use try catch statement to handle exceptions of the type Exception, and display a simple error message if any exception happens. You don t need to write any import statements. (12 marks) 10 marks for all statements (as distributed below) try { (1 mark) URL address = new URL(" (2 marks) BufferedReader in = new BufferedReader(new InputStreamReader(address.openStream()));(2 marks) System.out.println(in.readLine());(2 marks) in.close();(1 mark) catch (Exception ex) { (1 mark) System.out.println("ERROR!"); (1 mark) M257 Final - Form A 5/5