Midterm assessment Spring The Solution

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1 Faculty of Computer Studies Information Technology and Computing Date: /4/2011 Duration: 90 minutes M : P u t t i n g J a v a t o W o r k Midterm assessment Spring The Solution Student Name: Section Number Student ID: 1-Version 1 IMPORTANT INSTRUCTIONS 1. This exam has 3 parts and ALL questions must be answered. 2. This exam consists of 7 pages. 3. Student handbooks are NOT permitted in this examination. 4. The use of electronic devices that could have a memory is NOT permitted. 5. At the end of the examination: a. Check that you have written your student ID, name and your section number on the first page. b. Put your answer book and your question paper together and give them to the exam invigilator.

2 Part I Multiple Choice Questions [15 points] Question 1 This question consists of 10 multiple choice questions. Attempt all questions. [1.5 points each] 1 Which of the following attempts to create initialized variables would cause a compilation error? a- float j = 1.2; b- int k = -200; c- char ok = 1; d- char mychar = \n ; 2 18 / 12 = a- 1.5 b- 6 c- 0 d- 1 3 Which of the following combined declarations and initialization is wrong? a- boolean bob = true ; b- boolean sue = true; c- boolean value = false ; d- Boolean f = false; 4 Which of the following array-initializing expression is false? a- int [] f = {10, 20; b- boolean b[] = {FALSE, TRUE, FALSE; c- String s[] = { FALSE, TRUE ; d- char [] chara = { a, b, c ; 5 Which of the following is false? a- char [] ch = new char [5]; b- boolean [] b = new boolean[3]; c- int [] f = new int[-1]; d- int [] byte = new byte[10]; 2

3 Part I Multiple Choice Questions [15 points] 6 For each type of robot that you have learnt about in unit 2, an object of each type is created as shown below, based on these declarations and creation Java statements, which of the method invocations is invalid? a- vsr.moveto(5,4); Robot r = new Robot(); MagicRobot mr = new MagicRobot(); SpeedRobot sr = new SpeedRobot(); VariableSpeedRobot vsr = new VariablSpeedRobot(); b- Boolean cansee = mr.isvisible(); c- r.movesouth; d- sr.movenorth(); 7 Which of the following Java methods headers is a constructor of the class Teacher? a- public Teacher Teacher() b- public void Teacher() c- public Teacher d- public Teacher() 8 Assume Employee and Parent are classes; Comparable and Serializable are standard Java interfaces. Which of the following declarations is invalid? a- class MonthlyEmployee extends Employee, Parent implements Comparable b- class MonthlyEmployee implements Comparable, Serializable c- class MonthlyEmployee implements Comparable d- class MonthlyEmployee extends Employee implements Comparable 9 Which of the following constant names conform to the Java naming conventions? a- Degree b- DEGREE c- degree d- a and c 10 Given that x = ay 3 +9, which of the following expressions is a correct Java statement for this equation. a- x = a * y * (y * y + 9); b- x = a * y * y * (y + 9); c- x = ( a * y ) *y * (y + 9); d- x = (a * y) * y * y + 9; 3

4 Part II Short Answers Questions [30 points] Question 1 Write 4 different Java statements that each subtracts 1 from the integer variable z. [8 points] z = z - 1; z -=1; --z; z--; Question 2 Find the error in the following 4 Java program segments. Explain how to correct the error. [10 points] a public int product() { int a=6, b=5, c=4; double result; result = a * b * c; System.out.println( Result is: + result); return result; b public void f(float a);{ System.out.println(a); c public int double product() { int a=6, b=5, c=4, result; result = a * b * c; System.out.println( Result is: + result); return result; (3 points) public int g(){ System.out.println( Inside method g ); public int h(){ System.out.println( Inside method h ); public int g(){ System.out.println( Inside method g ); public int h(){ System.out.println( Inside method h ); (2 points) d public void f(float a);{ System.out.println(a); (2 points) public int sum(int n){ if(n==0) return 0 else n*n; public int sum(int n){ if(n==0) return 0; else return n*n; (3 points) Question 3 For the following code, state the scope of the variables: x, y and z. [6 points] public class Calculations { int x; public void addnumbers(int y){ int z; z = x + y; The scope of the variable x is the whole Calculations class The scope of the variable y is inside the block of the method addnumbers. The scope of the variable z is inside the block of the method addnumbers. Question 4 List 4 common examples of exceptions [6 points] Memory exhaustion, array index out of bounds, arithmetic overflow, division by Zero, invalid method parameters, 4

5 Part III Problem Solving Questions [55 points] Question 1 [5 points] Write the Java declaration statements that describe the class headers of the 3 classes shown in the following class diagram. Question 2 public abstract Item public class PrintedItem extends Item public class Book extends PrintedItem [5 points] Given the following code, what output would you expect? public class Parent { public void method (int i){ System.out.println("Parent" + i); public class Child extends Parent { public void method(int i){ System.out.println("Child" + i*2); public class TestChildParent { public static void main(string [] args){ Parent q = new Child(); Parent p = new Parent(); Child c = new Child(); c.method(1); p.method(2); q.method(3); Child2 Parent2 Child6 Question 3 [20 points] In this question you will generate a multiplication table and write it to a text file. Here is a picture of what the text file will look like =========================== Multiplication Table =========================== line1: line2: line3: line4: =========================== Write a Java class called MultiplicationTable so that meets the following specifications: 1- Imports on demand the classes of package io. 5

6 Part III Problem Solving Questions [55 points] 2- Declares a PrintWriter object which is referenced by the variable out. This object will be used later in the printmultiplacationtable method for writing data to the text file table.txt. 3- Declares a constant class variable, MAX_LINES, of type integer and equals to 4. [2 points] 4- Consists of a method called openfile(string filename) so that it meets the following specifications: a- Throws the FileNotFoundException exception. b- Creates the PrintWriter object mentioned in point Consists of a method called printmultiplicationtable which displays exactly the multiplication table as shown above [6 points] 6- Consists of a method called closefile() which invokes the close() method of the PrintWriter class. 7- Write a new class called TestMultiplicationTable to test the MultiplicationTable class so that it meets the following specification: a- Creates a MultiplicationTable object. b- Invokes the openfile() method to open the textfile table.txt. c- Invokes the printmultiplicationtable() method to write the multiplication table to the text file table.txt. d- Invokes the closefile() method. import java.io.*; public class MultiplicationTable { PrintWriter out; final static int MAX_LINES = 4; public void openfile(string filename) throws FileNotFoundException{ out = new PrintWriter(fileName); public void printmultiplicationtable(){ out.println("==========================="); out.println(" Multiplication Table"); out.println("==========================="); for(int i=1; i<=max_lines; i++){ out.print("line"+i+":"); for(int j=1; j<max_lines; j++){ out.print("\t"); out.print(i*j); out.println(); out.println("==========================="); public void closefile(){ out.close(); import java.io.*; public class TestMultiplicationTable { 6

7 Part III Problem Solving Questions [55 points] public static void main(string [] args) throws FileNotFoundException{ MultiplicationTable table = new MultiplicationTable(); table.openfile("d:\\table.txt"); table.printmultiplicationtable(); table.closefile(); Question 4 Below you are given the class Item. [25 points] public class Item { String itemname, String itemcode; int unitprice; public Item(String name, String code, int price){ itemname = name; itemcode = code; unitprice = price; public String getitemname(){return itemname; public String getitemcode(){return itemcode; public int getunitprice(){return unitprice; public void setitemname(string name){itemname = name; public void setitemcode(string code){itemcode = code; public void setunitprice(int price){unitprice = price; Based on the Item class shown above, write a new class Bill that implements the following specifications: 1- Imports on demand the classes of the package util. 2- Declares the instance variable itemlist of type ArrayList<Item>. 3- Consists of a constructor which creates an ArrayList<Item> objects and makes itemlist point to it. [2 points] 4- Consists of a method called additem(item item) which adds an item to the array list. [2 points] 5- Consists of a method called removeitem(item item) which removes an item from the array list. This method is provided so that errors can be corrected, or so that the user can amend their order. [2 points] 6- Consists a method called printbill() which prints out the name of each item in the array list, with its unit cost in pence, calculates the total amount as it goes along, and prints the total, also in pence, at the end of the list, e.g. [10 points] Item 1: The Java Collection Classes cost 1200 Item 2: Favourites from the Palm Court Orchestra cost 399 Total amount: 1599 Thank you for visiting us. Please come again. This method makes use of methods getunitprice and getitemname specified in the Item class. 7

8 Part III Problem Solving Questions [55 points] 7- Write a new class TestClass to test the Bill class so that implements the following specifications. [6 points] a- Create a Bill object. b- Create 3 Item objects. c- Add the created Item objects in part b to created Bill object in part a. d- Remove one of the added Item objects in part c. e- Print a bill for the remaining Item objects. import java.util.*; public class Bill{ private ArrayList<Item> itemlist; public Bill(){ itemlist = new ArrayList<Item>(); public void additem(item item){ itemlist.add(item); public void removeitem(item item){ itemlist.remove(item); public void printbill(){ int totalamount = 0; Item item = null; for (int i = 0; i < itemlist.size(); i++){ item = itemlist.get(i); totalamount = totalamount + item.getunitprice(); System.out.println("Item " + (i + 1) + ": " + item.getitemname() + " cost " + item.getunitprice()); System.out.println("Total amount: " + totalamount + "\n\nthank you for visiting us. Please come again."); import java.util.*; public class TestClass{ public static void main(string[] args){ Bill mybill = new Bill(); Item item1 = new Item("Java Book", "p042", 15); Item item2 = new Item("Software Tool", "15jq9", 5); Item item3 = new Item("C++ Book", "w12x3", 10); mybill.additem(item1); mybill.additem(item2); mybill.additem(item3); mybill.removeitem(item3); mybill.printbill(); The End 8