Lecture 2

Lecture-2
Instructor Name:
Object Oriented Programming

Today’s Lecture
 Information Hiding
 Encapsulation
 Interface
 Implementation
 Abstraction
2

Information Hiding
Introduction
 Information hiding is one the most important principle of OOP which says the
private information should only be accessible to the owner.
 Information Hiding means “Showing only those details to the outside world
which are necessary for the outside world and hiding all other details from the
outside world.”
 Information is stored within the Object
 Information within the object is not accessible to outside world
 Information can only be manipulated by the object
3

Information Hiding
Introduction
 Information hiding: a module is characterized by the information it hides from
other modules, which are called its clients. The hidden information remains a
secret to the client modules. (Ghezzi et al)
 The purpose of Information hiding is to make inaccessible certain details that
should not affect other parts of a system. (Ross et al)
 Information hiding is the principle that users of a software component (such as a
class) need to know only the essential details of how to initialize and access the
component, and do not need to know the details of the implementation. (Budd)
4

Information Hiding
Information Hiding – Real Life Examples
 A Person’s (Say Ali) name other information is stored in this brain and we can not
access it directly
 An Email server has millions of email address but it shares only our account
information with us
 A phone SIM card may store several phone numbers but we can not read numbers
directly rather a phone set (a person’s own) will read this information for us
5

Information Hiding
Information Hiding in OOP’s Perspective
 In OOP an Object have state and behaviors that is hidden from outside world. So
in OOP perspective information hiding is
“Hiding object detail (state & behavior) from the users”
 Term “user” defined here means an “Object” of another class that is calling
functions of this class using or it may be another program in which we are using
this class.
6

Information Hiding
Advantages of Information Hiding
 Simplifies Object Oriented Model
In OOP Model we only have object and their interaction
 Barrier against change propagation
Any change in the functionality doesn’t effect the OOP model
7

Information Hiding
Achieving Information Hiding
 Information hiding can be achieved using
1. Encapsulation
2. Abstraction
8

Encapsulation
What is Encapsulation?
 Encapsulation means “All the characteristics of an object are hidden in the
object itself”.
 The wrapping up of data and function into a single unit is known as
encapsulation.
 Encapsulation hides the implementation details
 Encapsulation and information hiding are the same concepts so they may be
used as synonyms.
10

Encapsulation
Encapsulation and Object
 Data and Behaviour are tightly coupled inside an object
 Information structure and implementation details of its operations are hidden
from outside world.
11

Encapsulation
Encapsulation Example
 A Person (Say Ali) stores his personal information in itself and its behaviour is
also implemented in it. (Ali is an object of person)
 Now its up to Object Ali whether he wants to share this information with
outside world or not.
 Attributes and Behaviour of Ali are encapsulated in itself. 12

Encapsulation
Encapsulation Example
 A Phone stores phone numbers in digital format and knows how to convert it
into human-readable characters
 We don’t know
 How the data is stored
 How it is converted to human-readable characters
13

Encapsulation
Advantages of Encapsulation
 Followings are the advantages of Encapsulation
1. Simplicity and Clarity
2. Low Complexity
3. Better Understanding
4. Ensure Structural Changes remain Local
5. Encapsulation Allows adding some logic when accessing client’s
data
For Example validation on modifying a property
14

Interface
Object and Interface
 Every Object has an Interface.
 Interface is set of functions of an object that he wants to expose to other
objects.
 An object encapsulates data and behaviour. So how will an object interact
with other objects?
 Objects communicate through this interface.
15
What would be the interface of a Phone?

Implementation
Object and Implementation
 The behaviour of object requires implementation.
 The actual implementation (coding) of the behaviour in any object oriented
language is called implementation.
 Implementation has two parts
1. Internal Data Structures to hold an object state that will be hidden from us
2. Functionality in the form of member functions to provide required
behaviour
 Example – Implementation of Gear Box
Data Structure
– Mechanical structure of gear box
Functionality
– Mechanism to change gear 16

Implementation
Object and Implementation
 What would be the implementation of an Address Book in a Phone
• Data Structure
– SIM card
• Functionality
– Read/write circuitry
17

Interface & Implementation
Separation of Interface & Implementation
 Only Interface of object is shown and implementation detail is hidden.
 Separating implementation detail from interface is very beneficial as Interface
becomes independent of implementation detail
Real Life Example of Separation of Interface & Implementation
 Driver has a standard interface to drive a car and using that interface he can
drive car of any model or any engine type
18

Messages
What is a message in OOP?
 A message is a request for an object to perform one of its operations (methods)
 All Communication between objects is done via messages
 The number and kind of messages that can be sent to an object depends upon
its interface
 The object to which message is addressed (yourBicycle)
 The name of the method to perform (changeGear)
 Any parameter needed by the method (lowerGear)
19

Messages
What is a message in OOP?
20
SHOULD WE INCLUDE THIS SLIDE ?

Abstraction
What is Abstraction?
 Abstraction means ignoring irrelevant features, properties, or functions and
emphasizing the relevant one
 …relevant to the given project (with an eye to future reuse in similar projects)
Abstraction = managing complexities
21

Abstraction
What is Abstraction?
 Abstraction is something we do everyday
 Looking at an object , we see those things about it that have
meanings to us.
 We abstract the properties of the object, and keep only what we
need.
 Abstraction allows us to represent a complex reality in terms of
simplified model
 Abstraction highlights the properties of an entity that we are most
interested in and hides the other 22

Abstraction
Abstraction Example
“Ali is PHD student and teaches BS students”
 Here Object Ali has two perspective one is student perspective and
other is teacher perspective.
Attributes
Student Perspective Teacher Perspective
Name Employee ID
Student Roll No Designation
Year of Study Salary
CGPA Age
 Age is common attribute in both perspectives
23

Abstraction
Abstraction Example
“Ali is PHD student and teaches BS students”
 Here Object Ali has different behaviors in student perspective and
teacher perspective.
Behavior
Student Perspective Teacher Perspective
Study Deliver Lecture
GiveExam TakeExam
PlaySports DevelopExam
24

Abstraction
Abstraction Example
“A cat can be viewed with different perspectives”
 Here Object Cat has different perspective on Ordinary perspective and
Surgeon perspective.
Ordinary Perspective Surgeon’s Perspective
A pet animal with A being with
Four Legs A Skeleton
A Tail Heart
Two Ears Kidney
Sharp Teeth Stomach
25

Abstraction
Abstraction Example
Driver’s View Engineer’s View
26

Abstraction
Abstraction Advantage
 Abstraction has following advantages
 Simplifies the model by hiding irrelevant details
 Abstraction provides the freedom to defer implementation
decisions by avoiding commitment to details.
27

Lecture 2

More Related Content

What's hot (20)

Viewers also liked (10)

Similar to Lecture 2 (20)

More from talha ijaz (16)

Recently uploaded (20)

Lecture 2

Editor's Notes