1. Object-Oriented Programming (part 1 – Data Encapsulation)
INF230 Basics in C# Programming
AUBG, COS dept
Lecture 21
Title:
Object-Oriented Programming
(part 1 – Data Encapsulation)
Reference: Doyle, chap 4

2. Lecture Contents: Components of a class
Methods and properties used for object-oriented development
Constructors
Own instance methods mutators/accessors
Call instance methods including mutators and accessors

3. Chapter 4 Creating Your Own Classes C# Programming:
From Problem Analysis to Program Design
4th Edition

4. Informal introduction to concept of classes/objects
Transition
From Structured Programming to OOP
From Think in Functions to Think in Objects
From Algorithms + Data Structures = Programs
To Classes + Objects = Programs

5. Formal introduction to concept of classes/objects
OOP (Object Oriented Programming):
Data Encapsulation & Data Hiding
Inheritance
Polymorphism …

6. 3 main OOP characteristics
Data Encapsulation/Data Hiding
Data and its routines /named methods/ are said to be encapsulated into a single entity.
Data is concealed within a class, so that it cannot be accessed mistakenly from methods outside the class.
Inheritance
Polymorphism

7. 3 main OOP characteristics
Data Encapsulation and Data Hiding
Inheritance
The process of creating new classes, called derived classes from existing classes or base classes
Polymorphism

8. 3 main OOP characteristics
Data Encapsulation and Data Hiding
Inheritance
Polymorphism
Generally, the ability to appear in many forms, or in other words Giving different meanings to the same thing
More specifically, in OOP it is the ability to redefine methods for derived classes

9. 3 main OOP characteristics
Data Encapsulation and Data Hiding
Inheritance
Polymorphism
And many other, e.g.
Abstract classes
Interfaces …

10. The Object Concept
Solution is defined in terms of a collection of cooperating objects
Class serves as template from which many objects can be created
Abstraction
Attributes (data)
Behaviors (processes on the data)
C# Programming: From Problem Analysis to Program Design

11. Class SmallObj - definition{
private int somedata;
public int getSomeData() { return somedata; }
public void setSomeData(int d) { somedata = d; }
public void ShowData()
Console.WriteLine("\n\nData is = {0}", somedata); }
} // end of class

12. Class SmallObj – how to use?
static void Main(string[] args) {
SmallObj a = new SmallObj();
a.setSomeData(713);
Console.WriteLine(" {0}", a.getSomeData() );
a.ShowData();
. . .
Console.ReadKey(); }

13. Anatomy of a Class Class components: Member data /fields/ Methods
Constructors
Accessors / Mutators
In stance Methods and Class Methods
Properties
Events

14. Private Member Data All code you write is placed in a class
When you define a class, you declare instance variables or fields that represent state of an object
Fields are declared inside the class, but not inside any specific method
Fields become visible to all members of the class, including all of the methods
Data members are defined to have private access
C# Programming: From Problem Analysis to Program Design

15. Private Member Data (continued)
public class Student { private int studentNumber; private string studentFirstName; private string studentLastName; private int score1; private int score2; private int score3; private string major; …
C# Programming: From Problem Analysis to Program Design

16. Private Member Data (continued)
public class CarpetCalculator { private double pricePerSqYard; private double noOfSqYards; …
C# Programming: From Problem Analysis to Program Design

17. Anatomy of a Class
Class components
Methods:
Constructors

18. Constructor Special type of method used to create objects
Create instances of class
Instantiate the class
Constructors differ from other methods
Constructors do not return a value
Also do not include keyword void
Constructors use same identifier (name) as class
Constructors use public access modifiers
C# Programming: From Problem Analysis to Program Design

19. Constructor (cont.) Do not use static keyword
Static associated with class method
Constructor – special type of instance method
Do not return a value
void is not included
Same identifier as the class name
Overloaded
Default constructor
No arguments
Write one constructor and you lose the default one
C# Programming: From Problem Analysis to Program Design

20. Constructor (continued)
public access modifier is always associated with constructors
//Default constructor
public Student ( ) { }
//Constructor with one parameter
public Student (int sID )
studentNumber = sID;
C# Programming: From Problem Analysis to Program Design

21. Constructor (continued)
//Constructor with three parameters
public Student (string sID, string firstName, string lastName) {
studentNumber = sID;
studentFirstName = firstName;
studentLastName = lastName; }
Design classes to be as flexible and as full-featured as possible
Include multiple constructors
C# Programming: From Problem Analysis to Program Design

22. Writing Your Own Instance Methods
In addition to Constructors
Accessors
Mutators
Other methods to perform behaviors of the class
C# Programming: From Problem Analysis to Program Design

23. Accessors Getters Returns the current value
Standard naming convention → prefix with “Get”
Accessor for noOfSquareYards
public double GetNoOfSqYards( ) {
return noOfSqYards; }
Properties serve purpose
Accessor
C# Programming: From Problem Analysis to Program Design

24. Mutators Setters Normally includes one parameter
Method body → single assignment statement
Standard naming convention → prefix with ”Set”
Can be overloaded
C# Programming: From Problem Analysis to Program Design

25. Mutator Examples Overloaded Mutator
public double SetNoOfSqYards(double squareYards) {
noOfSquareYards = squareYards; }
public void SetNoOfSquareYards(double length, double width)
// length, width – in feet; 1 yard = 3 feet; 1 sq.yard = 9 sq.feer
noOfSquareYards = length * width / 9;
Overloaded
Mutator
C# Programming: From Problem Analysis to Program Design

26. Other Instance Methods
No need to pass arguments to these methods –
Defined in the same class as the data members
Instance methods can directly access private data members
Define methods as opposed to storing values that are calculated from other private data members
public double CalculateAverage( ) {
return (score1 + score2 + score3) / 3.0; }
C# Programming: From Problem Analysis to Program Design

27. Anatomy of a Class
Class components:
Properties

28. Property Can replace accessors and mutators
Properties look like a data field
More closely aligned to methods
Standard naming convention in C# for properties
Use the same name as the instance variable or field, but start with uppercase character
Doesn’t have to be the same name – no syntax error will be thrown
C# Programming: From Problem Analysis to Program Design

29. Property public double NoOfSqYards { get return noOfSqYards; } set
// given data member noOfSqYards. See the property NoOfSqYards below:
public double NoOfSqYards {
get
return noOfSqYards; }
set
noOfSqYards = value;
C# Programming: From Problem Analysis to Program Design

30. Property (continued)
If an instantiated object is named berber, to change the NoOfSqYards, write:
berber.NoOfSqYards = 45.60;
C# Programming: From Problem Analysis to Program Design

31. Property (continued)
If an instantiated object is named berber, to get value of data member associated to /i.e. hidden behind/ the property NoOfSqYards, write:
double var;
var = berber.NoOfSqYards;
Console.WriteLine(“{0}”, berber.NoOfSqYards);
C# Programming: From Problem Analysis to Program Design

32. Property (continued) Given a class Employee and data member salary
private decimal salary;
See the property Salary below:
If an instantiated object is named peter, to update /i.e. modify – increase or decrease/ value of data member salary associated to /i.e. hidden behind/ the property Salary, write:
peter.Salary = peter.Salary M;
peter.Salary -= M;
C# Programming: From Problem Analysis to Program Design

33. Anatomy of a Class Class components:
Inheritance relation and access to base class methods

34. ToString( ) Method
All user-defined classes inherit four methods from the object class
ToString( )
Equals( )
GetType( )
GetHashCode( )
C# Programming: From Problem Analysis to Program Design

35. ToString( ) Method
ToString( ) method is called automatically by several methods
Write( )
WriteLine( ) methods
Can also invoke or call the ToString( ) method directly
C# Programming: From Problem Analysis to Program Design

36. ToString( ) Method (continued)
Returns a human-readable string
Can write a new definition for the ToString( ) method to include useful details
public override string ToString( )
{ // return string value }
Keyword override added to provide new implementation details
Always override the ToString( ) method
This enables you to decide what should be displayed if the object is printed
C# Programming: From Problem Analysis to Program Design

37. ToString( ) Example
public override string ToString( ) { return "Price Per Square Yard: " + pricePerSqYard.ToString("C") + "\nTotal Square Yards needed: " + noOfSqYards.ToString("F1") + "\nTotal Price: " + DetermineTotalCost( ).ToString("C"); }
C# Programming: From Problem Analysis to Program Design

38. ToString( ) method
Sometimes useful to add format specifiers as one of the arguments to the Write( ) and WriteLine( ) methods – Invoke ToString( )
Numeric data types such as int, double, float, and decimal data types have overloaded ToString( ) methods
pricePerSqYard.ToString("C")
C# Programming: From Problem Analysis to Program Design

39. Anatomy of a Class
Calling methods

40. Calling Instance Methods
Instance methods are nonstatic method
Call nonstatic methods with objects – not classes
Static calls to members of Math and Console classes
answer = Math.Pow(4, 2)
Console.WriteLine( )
If you need to invoke the method inside the class it is defined in, simply use method name
If you need to invoke the method outside the class it is defined in, precede method name with object identifier
berber.GetNoOfSquareYards( )
C# Programming: From Problem Analysis to Program Design

41. Calling the Constructor
Normally first method called
Creates an object instance of the class
ClassName objectName = new ClassName(argumentList); or
ClassName objectName;
objectName = new ClassName(argumentList);
Keyword new used as operator to call constructor methods
CarpetCalculator plush = new CarpetCalculator ( );
CarpetCalculator pile = new CarpetCalculator(37.90,17.95);
C# Programming: From Problem Analysis to Program Design

42. Constructor (continued)
Default values are assigned to variables of the value types when no arguments are sent to constructor
C# Programming: From Problem Analysis to Program Design

43. Calling the Constructor Method
Figure 4-4 Intellisense displays available constructors
C# Programming: From Problem Analysis to Program Design

44. Using Public Members Figure 4-5 Public members of the Student class
C# Programming: From Problem Analysis to Program Design

45. Calling Accessor and Mutator Methods
Method name is preceded by the object name
Calling mutator method
berber.SetNoOfSquareYards(27.83);
Calling accessor method
Console.WriteLine("{0:N2}", berber.GetNoOfSquareYards( ));
C# Programming: From Problem Analysis to Program Design

46. Using property instead of mutator methods
Method name is preceded by the object name
berber.SetNoOfSquareYards(27.83);
If property defined, can use property instead of mutator methods
PropertyName = value; // Acts like mutator here
NoOfSquareYards = 27.83;
C# Programming: From Problem Analysis to Program Design

47. Using property instead of accessor methods
Method name is preceded by the object name
Console.WriteLine("{0:N2}", berber.GetNoOfSquareYards( ));
If property defined, can use property instead of accessor methods
Console.WriteLine("{0:N2}", berber.NoOfSquareYards);
// Property Acts like accessor here
C# Programming: From Problem Analysis to Program Design

48. Calling Other Instance Methods
Call must match method signature
If method returns a value, must be a place for a value to be returned
Student aStudentObject = new
Student("1234", "Maria", "Smith", 97, 75, 87, "CS");
average = aStudentObject.CalculateAverage( );
No arguments needed as parameters to the CalculateAverage( ) method. CalculateAverage( ) is a member of the Student class and has full access to all Student members.
C# Programming: From Problem Analysis to Program Design

49. Testing Your New Class
Different class is needed for testing and using your class
Test class has Main( ) in it
Construct objects of your class
Use the properties to assign and retrieve values
Invoke instance methods using the objects you construct
C# Programming: From Problem Analysis to Program Design

50. User classes and Test class
using System;
namespace MyUserClasses {
public class Student }
//=====================================
namespace TestUserClasses
using MyUserClasses;
class Test
public static void Main()

51. Test Class
With multiclass solutions all input and output should be included in the class that has the Main( ) method
Eventual goal will be to place your class files, like Student and CarpetCalculator, in a library so that the classes can be used by different applications
Some of these applications might be Windows applications; some may be console applications; others may be Web application
Do not include ReadLine( ) or WriteLine( ) in your class methods
C# Programming: From Problem Analysis to Program Design

52. Testing Your New Class Figure 4-7 Output from Carpet example using
instance methods
C# Programming: From Problem Analysis to Program Design

53. How to create a class
By hand – typing all the source text concerning the class template – as it was done with SmallObj class
Using a number of tools available in Visual Studio to aid in the development of applications
To add a second class in your application, use the PROJECT menu or Solution Explorer window

54. Add a Class Use the PROJECT menu or the Solution Explorer Window
Select your project file, then Right-mouse click and select the option Add, Class
Solution Explorer Window enables you to create a class diagram
C# Programming: From Problem Analysis to Program Design

55. Open the Class Diagram from Solution Explorer, View Class Diagram
Figure 4-1 Student class diagram created in Visual Studio
C# Programming: From Problem Analysis to Program Design

56. Class Diagram (continued)
After the class diagram is created, add the names of data members or fields and methods using the Class Details section
Right click on class diagram to open Class Details window
Figure 4-2 Student class diagram details
C# Programming: From Problem Analysis to Program Design

57. Class Diagram (continued)
When you complete class details using the Class Diagram tool, code is automatically placed in the file.
Figure 4-3 Auto generated code from Student class diagram
C# Programming: From Problem Analysis to Program Design

58. Practical exercises .

59. Class SmallObj Modify the SmallObj class:
Ignore ShowData() method as unnecessary
Define property SOMEDATA associated with somedata field
Demonstrate how to use the property.
SmallObj a = new SmallObj();
a.SOMEDATA = 5555;
Console.WriteLine("\n\n\n{0}", a.SOMEDATA);

60. Class SparePart Develop a class with data members – fields:
int modelno, int partno, double cost
And
Constructors
No arg, 3-arg
Accessor/Mutator methods
Properties
Modelno
Partno
Cost

61. Class Counter Develop a class with data members – fields: int count
And
Constructors
No arg, 1-arg
Accessor/Mutator methods
Property
Count

62. Class Distance Develop a class with data members – fields: int feet
double inches
Constructors
No arg, 1-arg (2 copies), 2-arg
Accessor/Mutator methods
Properties
Feet
Inches

63. Class Point Develop a class with data members – fields: int xcoord
int ycoord
Constructors
No arg, 2-arg
Accessor/Mutator methods
Properties
Xcoord
Ycoord

64. Class Circle Develop a class with data members – fields:
int xcoord int ycoord double radius
Constructors
No arg, 3-arg
Accessor/Mutator methods
Properties
Xcoord
Ycoord
Radius

65. Thank You
For
Your Attention!

66. RealEstateInvestment Example
Figure 4-8 Problem specification for RealEstateInvestment example
C# Programming: From Problem Analysis to Program Design

67. Data for the RealEstateInvestment Example
Table 4-2 Instance variables for the RealEstateInvestment class
C# Programming: From Problem Analysis to Program Design

68. Data for the RealEstateInvestment Example (continued)
Table 4-3 local variables for the property application class
C# Programming: From Problem Analysis to Program Design

69. RealEstateInvestment Example (continued)
Figure 4-9 Prototype
C# Programming: From Problem Analysis to Program Design

70. RealEstateInvestment Example (continued)
Figure Class diagrams
C# Programming: From Problem Analysis to Program Design

71. RealEstateInvestment Example (continued)
Table 4-4 Properties for the RealEstateInvestment class
C# Programming: From Problem Analysis to Program Design

72. RealEstateInvestment Example (continued)
Figure Structured
English for the
RealEstateInvestment
example
C# Programming: From Problem Analysis to Program Design

73. Class Diagram Figure 4-12 RealEstateInvestment class diagram
C# Programming: From Problem Analysis to Program Design

74. Test and Debug Figure 4-13 Output from RealEstate Investment example
C# Programming: From Problem Analysis to Program Design