OOP programming for engineering students

Principles of Object Oriented
Programming (OOP)
Presentation
On
By
Mr. Shibdas Dutta
Company Confidential: Data-Core Systems, Inc. | datacoresystems.com

2
Topics to be Covered
• Overview of OOP
• Concepts of OOP
• Principles of OOP
• Why OOP
• Relationships in OOP
• Conclusions
• Questions

3
Overview of OOP
 OOP has roots from 1960s when h/w & s/w became
increasingly complex, and also quality often
compromised.
 Uses “Object” which interacts with design applications
and programs.
 Focuses on “data” rather “process”.
 Programs composed of “Object” i.e. “Modules”.
 Object contains all “data” to manipulate its own data
structure unlike modular programming which focused to
“function”.

4
Overview of OOP (Contd…)
 Collection of “co-operating” object rather “sub-routines”.
 Each object is capable of receiving messages,
processing data and sending messages to other object.
 “Object” can be viewed as an independent “machine”
with distinct role.
 For example: Smalltalk, Ruby, Simula, Algol, Python,
C++, Java to mention a few.
 Remember, Smalltalk is the first OOP.

5
Concept Of OOP
Fundamental concepts of OOP are as follows:
 Class
 Object
 Instance & Object State
 Method
 Message Passing

6
Class
 Is a “blueprint” or “factory” that describes the “nature” of
“some-thing”
 “nature” – is thing’s characteristics (i.e. ‘attributes’, ‘fields’
or ‘properties’) and behaviors (i.e. ‘thing’s can do’ and
‘method/features’).
 “some-thing” – is the “Object” itself.
 For example: the class DOG would consists of
characteristics shared by all dogs, such as no. of legs,
color etc. and the ability to bark and sit are the behaviors.

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Object
 A pattern of a class i.e. class DOG defines all
possible dogs by listings the characteristics and
behaviors they can have.
 The object Lassie is one particular dog, with
particular versions of the characteristics.
Obj1-Lassie
Obj2-Labrador
Obj3-Breeder
Class DOG
Legs
Color
Ear
Bark()
Sit()
Walk()

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Instance & Object State
 When Object is in runtime position, is called Instance.
 The Lassie object is an instance of the DOG class.
 The set of all values of the attributes of a particular object
is called its “state”.
 For example: Class.DOG (no_of_Legs,Color,Ear_type);
Obj1.Lassie (‘4’,”Yellow”,”Thin & Long”);
Obj2.Labrador (‘4’,”Green”,”Big”);
Obj3.Breeder (‘4’,”White”,”Very Small”);
Object State

9
Method
 An object’s ability.
 For example: Lassie, being a dog, has the ability to bark,
so bark() is one of Lassie’s method.
 Similarly, sit(), eat() and walk() are also methods of Lassie
object.
Generally, all behaviors of object should be represented
by methods() in program.

10
Message Passing
 The process by which an object sends data to another
object or asks the other object to invoke a method.
 For example: the object called Breeder may tell the
Lassie’s object to sit by passing a “SIT Down” message
which invokes Lassie’s “Sit” method.
Sit() Sit()
“SIT Down”
Obj3. Breeder Obj1. Lassie

11
Principles of OOP
 There are many opinions of what it means for a
development systems or languages to be “Object
Oriented”.
 However, it is widely agree that any language that claims
to be object oriented must at least support:
Encapsulation, Data Abstraction,
Inheritance and Polymorphism.

12
Encapsulation
 Is the hiding of data implementation by restricting access
to “accessor” and “mutator”.
 “accessor” – is a method to “access” the data/info. of
object by using get method as following program:
( I am using VB.Net since in my opinion it is easier to read and understand positively
)
Public Class Person
Private _fullName As String = "Raymond Lewallen"
Public ReadOnly Property FullName() As String
Get
Return _fullName
End Get
End Property
End Class

13
Encapsulation (Contd…)
 “mutator” – is a public method to “modify” the data/info. of an object
using set method as following program:
Public Class Person
Private _fullName As String = "Raymond Lewallen“
Public Property FullName() As String
Get
Return FullName
End Get
Set(ByVal value As String)
_fullName = value
End Set
End Property
End Class
This type of data protection and implementation protection without breaking
the other code that is using in rest of the program, is called Encapsulation.

14
Data Abstraction
 It is the simplest principle to understand.
 Is the developments of classes and objects rather
implementations details.
 It denotes a “model” or “view” of item (object).
 It is used to manage complexity by decompose complex
system into smaller components.
Definition: “An abstraction denotes the essential
characteristics of an object that distinguish it from all
other kinds of object and thus provide defined conceptual
boundaries, relative to the perspective of the viewer”.

15
Data Abstraction (Contd…)
Public Class Person
Private _height As Int
Public Property Height() As Int
Get
Return _height
End Get
Set(ByVal Value As Int)
_height = Value
End Set
End Property
Lets, look at this code for a person object
(“height”,”weight” and “age” as attributes).
 Private _weight As Int
 Public Property Weight() As Int
 Get
 Return _weight
 End Get
 Set(ByVal Value As Int)
 _weight = Value
 End Set
 End Property

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Private _age As Int
Public Property Age() As Int
Get
Return _age
End Get
Set(ByVal Value As Int)
_age = Value
End Set
End Property
 Public Sub Sit()
 // Code that makes the person sit
 End Sub
 Public Sub Run()
 // Code that makes the person run
 End Sub
 Public Sub Cry()
 // Code that make the person cry
 End Sub
 Public Function CanRead() As Boolean
 // Code that determines if the person can read
// and returns a true or false
 End Function
 End Class

17
 So, I have create a software model of a person object.
 I have created an abstract type of what a person object is to us
outside of the software world.
 The abstract person is defined by the operations that can be
performed on it, and the information we can get from it and give to it.
 What does the abstracted person object look like to the software
world that doesn't have access to its inner workings?
 Can't really see what the code is that makes the person run!!!
So, in short, data abstraction is nothing more than the implementation of
an object that contains the same essential properties and actions, we
can find in the original object we are representing.

18
Inheritance
 Objects can relate to each other with either a “has a”,
“uses a” or an “is a” relationship.
 “Is a” is the inheritance way of object relationship.
 For example, take a library inventory system.
 Lets, A library lends Book, Magazine, Audiocassette
and Microfilm to people.
On some level, these are treated the same due to some features
should be common but are not identical because a book has an
ISBN and a magazine does not or audiocassette has a play length
where as microfilm cannot be checked out overnight!!

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Inheritance (Contd…)
 Each of these library’s loanable assets should be represented
by its own class definition named “LibraryAsset”, called a
superclass or base class.
 All assets i.e. (Book, Magazine, Audiocassette and Microfilm)
are sub classes or derived classes, so they inherit base class
characteristics.
 All assets have a title, a date of acquisition, a replacement
cost and checked out or available for checked out.
 Let us look at “LibraryAsset” Base class. This will be used as
the base class for Sub class “Book” :

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LibraryAsset { }
Title
Author
Dt._Of_acquisition
Checked_Out
ISBN
Replacement_Cost
Book { } Magazine { } Audiocassette { } Microfilm { }
Zone Play_Length Film_Color

21
Public Class LibraryAsset
Private _title As String
Public Property Title() As String
Get
Return _title
End Get
Set(ByVal Value As String)
_title = Value
End Set
End Property
 Private _checkedOut As Boolean
 Public Property CheckedOut() As Boolean
 Get
 Return _checkedOut
 End Get
 Set(ByVal Value As Boolean)
 _checkedOut = Value
 End Set
 End Property

22
Private _dateOfAcquisition As DateTime
Public Property DateOfAcquisition() As DateTime
Get
Return _dateOfAcquisition
End Get
Set(ByVal Value As DateTime)
_dateOfAcquisition = Value
End Set
End Property

23
Private _replacementCost As Double
Public Property ReplacementCost() As Double
Get
Return _replacementCost
End Get
Set(ByVal Value As Double)
_replacementCost = Value
End Set
End Property
End Class

24
The inheritance relationship is called the “is a” relationship. A book
“is a” LibraryAsset, as are the other 3 assets. Lets, look at the “Book”
sub class.
Public Class Book
Inherits LibraryAsset
Private _author As String
Public Property Author() As String
Get
Return _author
End Get
_author = Value
End Set
End Property
Private _isbn As String
Public Property Isbn() As String
Get
Return _isbn
End Get
_isbn = Value
End Set
End Property
End Class

25
Now, lets create an instance of the book class so we can record a
new book into the library inventory:
Dim myBook As Book = New Book
myBook.Author = "Sahil Malik"
myBook.CheckedOut = False
myBook.DateOfAcquisition = #2/15/2005#
myBook.Isbn = "0-316-63945-8"
myBook.ReplacementCost = 59.99
myBook.Title = "The Best Ado.Net Book You'll Ever Buy"
Hence, when we create a new book, we have all the properties of
the LibraryAsset class available to us as well, because we inherited
the class.
“One of the most powerful features of inheritance is the ability to
extend components without any knowledge of the way in which a
class was implemented”.

26
Polymorphism
 Polymorphism means one name, many forms.
 Polymorphism manifests itself by having multiple methods all with the
same name, but slighty different functionality.
 There are 2 basic types of polymorphism.
 Overloading, which is referred to as compile-time polymorphism.
 Overridding, also called run-time polymorphism.
 For method overloading, the compiler determines which method will
be executed, and this decision is made when the code gets
compiled.
 For method overrriding, which method will be used, is determined at
runtime based on the dynamic type of an object.

27
Polymorphism (Contd…)
Let’s look at some code of LibraryAsset class as following:
// Base class for library assets
Public MustInherit Class LibraryAsset
// Default fine per day for overdue items
Private Const _finePerDay As Double = 1.25
// Due date for an item that has been checked out
Private _dueDate As DateTime
Public Property DueDate() As DateTime
Get
Return _dueDate
End Get
Set(ByVal Value As DateTime)
_dueDate = Value
End Set
End Property

28
// Calculates the default fine amount for an overdue item
Public Overridable Function CalculateFineTotal() As Double
Dim daysOverdue As Int = CalculateDaysOverdue()
If daysOverdue > 0 Then
Return daysOverdue * _finePerDay
Else
Return 0.0
End If
End Function
// Calculates how many days overdue for an item being returned
Protected Function CalculateDaysOverdue() As Int
Return DateDiff(DateInterval.Day, _dueDate, DateTime.Now())
End Function
End Class

29
// Magazine class that inherits LibraryAsset
Public NotInheritable Class Magazine Inherits LibraryAsset
// No Overriding or Overloading of any function of Base
Class in Magazine class
// So, results will come as per Base class function definition
for this Magazine class
End Class

30
// Book class that inherits LibraryAsset
Public NotInheritable Class Book Inherits LibraryAsset
// This is the CalculateFineTotal() function of the base class.
// This function overrides the base class function, and any call to CalculateFineTotal
from any instantiated Book class will use this function, not the base class function.
// This type of polymorphism is called overriding.
Public Overrides Function CalculateFineTotal() As Double
Return daysOverdue * 0.75
Else
Return 0.0
End If
End Function
End Class

31
// AudioCassette class that inherits LibraryAsset
Public NotInheritable Class AudioCassette Inherits LibraryAsset
// This is the CalculateFineTotal() function (without parameter) of the base class.
// This is the CalculateFineTotal(double) function (with parameter) of the
audiocassette class.
// This function overrides the base class function, and any call to CalculateFineTotal()
from any instantiated AudioCassette Class will use this function, not the base class
function.
// This type of polymorphism is called overloading and overriding.
Public Overloads Overrides Function CalculateFineTotal() As Double
Return daysOverdue * 0.25
Else
Return 0.0
End If
End Function

32
// This is the CalculateFineTotal() function of the audiocassette class.
// This type of polymorphism is called overloading.
Public Overloads Function CalculateFineTotal(ByVal finePerDay As Double) As Double
If daysOverdue > 0 AndAlso finePerDay > 0.0 Then
Return daysOverdue * finePerDay
Else
Return 0.0
End If
End Function
End Class

33
Now lets look at some code that creates all these library items and
checks them in and calculates our fines based on returning them 3 days
late:
Public Class Demo
Public Sub Go()
// Set the due date to be three days ago
Dim dueDate As DateTime = DateAdd(DateInterval.Day, -3, Now())
ReturnMagazine(dueDate)
ReturnBook(dueDate)
ReturnAudioCassette(dueDate)
End Sub

34
Public Sub ReturnMagazine(ByVal dueDate As DateTime)
Dim myMagazine As Magazine = New Magazine
myMagazine.DueDate = dueDate
Dim amountDue As Double = myMagazine.CalculateFineTotal()
Console.WriteLine("Magazine: {0}", amountDue.ToString())
End Sub

35
Public Sub ReturnBook(ByVal dueDate As DateTime)
Dim myBook As Book = New Book
myBook.DueDate = dueDate
Dim amountDue As Double = myBook.CalculateFineTotal()
Console.WriteLine("Book: {0}", amountDue.ToString())
End Sub

36
Public Sub ReturnAudioCassette(ByVal dueDate As DateTime)
Dim myAudioCassette As AudioCassette = New AudioCassette
myAudioCassette.DueDate = dueDate
Dim amountDue As Double
amountDue = myAudioCassette.CalculateFineTotal()
Console.WriteLine("AudioCassette1: {0}", amountDue.ToString())
amountDue = myAudioCassette.CalculateFineTotal(3.0)
Console.WriteLine("AudioCassette2: {0}", amountDue.ToString())
End Sub
End Class

37
The output will look like the following:
Magazine: 3.75
Book: 2.25
AudioCassette1: 0.75
AudioCassette2: 9

38
Why OOP
 Facilitates team development.
 Easier to reuse software components and
write reusable software.
 Easier GUI (Graphical User Interface) and
multimedia programming.

39
Relationships in OOP
 Advantages of Object-Oriented programming language is code
reuse. This reusability is possible due to the relationship b/w the
classes.
 Object oriented programming generally support 4 types of
relationships that are: inheritance , association, composition and
aggregation.
 All these relationship is based on "is-a" relationship, "has-a"
relationship and "part-of” relationship.

Inheritance:
Inheritance is “IS-A” type of relationship.
 “IS-A” relationship is a totally based on Inheritance, which can be
of two types Class Inheritance or Interface Inheritance.
 Inheritance is a parent-child relationship where we create a new
class by using existing class code. It is just like saying that “A is
type of B”.
 For example is “Apple is a fruit”, “Ferrari is a car”.
 “HOD is a staff member of college” and “All teachers are staff
member of college”. For this assumption we can create a
“StaffMember” parent class and inherit this parent class in “HOD”
and “Teacher” class.
40 Company Confidential: Data-Core Systems, Inc. | datacoresystems.com

Composition:
Composition is a "part-of" relationship.
 composition means use of instance variables that are references
to other objects.
 In composition relationship both entities are interdependent of
each other for example “engine is part of car”, “heart is part of
body”.
 Let us take an example of car and engine. Engine is a part of each
car and both are dependent on each other.

Association:
Association is a “has-a” type relationship.
 Association establish the relationship b/w two classes using
through their objects.
 Association relationship can be one to one, One to many, many to
one and many to many.
 For example suppose we have two classes then these two
classes are said to be “has-a” relationship if both of these entities
share each other’s object for some work and at the same time
they can exists without each others dependency or both have their
own life time.
 For example, Employee and Manager relationship in an
organization.

Aggregation:
One class work as owner
 In association there is not any classes (entity) work as owner but in
aggregation one entity work as owner.
 In aggregation both entities meet for some work and then get
separated.
 Aggregation is a one way association.
 Let us take an example of “Student” and “address”. Each student
must have an address so relationship b/w Student class and
Address class will be “Has-A” type relationship but vice versa is not
true(it is not necessary that each address contain by any student).
So, Student work as owner entity.
 This will be a aggregation relationship.

44
Conclusions
 An OOP program models a world of active objects.
 An object may have its own “memory,” which may contain
other objects.
 An object has a set of methods that can process
messages of certain types.

45
Conclusions (Contd…)
 A method can change the object’s state, send messages
to other objects, and create new objects.
 An object belongs to a particular class, and the
functionality of each object is determined by its class.
 A programmer creates an OOP application by defining
classes.

46
Questions
Thanks for Patience!!!
?

OOP programming for engineering students

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