Lecture No.
01
01.1. Introduction
Course Objective:
Objective of this course is to make students familiar with the concepts of object
oriented programming. These concepts will be reinforced by their
implementation in C++.
Course Contents:
The main topics that we will study in the 45 lectures of this course are given
below,
Object Orientation
Objects and Classes
Overloading
Inheritance
Polymorphism
Generic Programming
Exception Handling
Introduction to Design Patterns
Recommended Text Book:
C++ How to Program ( Deitel & Deitel )
Reference Books:
1. Object-Oriented Software Engineering
By Jacobson, Christerson, Jonsson, Overgaard
(For object oriented programming introductory concepts)
2. The C++ Programming Language
By Bjarne Stroustrup
(For better c++ understanding)
Object-Orientation (OO)
What is Object-Orientation?
It is a technique in which we visualize our programming problems in the form of
objects and their interactions as happens in real life.
Examples:
We have different objects around us in our real life that interact with each other to
perform different operations for example,
A Person A House
A Tree A Car
Different Objects
These objects interact with each other to perform different operations,
Lives in
Ali House
Drives
Car Tree
Take another example of a School; the objects in a school are student, teacher, books,
pen ,school bag, classroom, parents, playground and so on… ,
Objects in a School
Teacher Student School Bag
Book Pen Playground
Parents Classroom Library
Suppose we want to develop a fee collection system for a school for this we will need to
find out related objects and their interactions as happens in real life.
In this way we can say that object orientation makes it easier for us to solve our real
world problems by thinking solution of the problem in terms of real world objects.
So we can say that in our daily life everything can be taken as an object that behaves in a certain
way and has certain attributes.
In object orientation we move our concentration to objects in contrast to procedural
paradigm in which we simply write our code in functions and call them in our main
program.
01.2. What is a Model?
A model is an abstraction of something real or conceptual.
We need models to understand an aspect of reality.
Model Examples
Highway maps
Architectural models
Mechanical models
01.3. OO Models:
In the context of programming models are used to understand the problem before
starting developing it.
We make Object Oriented models showing several interacting objects to understand
a system given to us for implementation.
Example 1– Object Oriented Model
lives-in
Ali House
drives
Car Tree
Objects Interactions
Ali, Car, House, Tree Ali lives in the house
Ali drives the car
Example 2– Object Oriented Model (A School Model)
A School Model
Teaches Plays-in
Teacher Student Playground
Has
Book Pen School Bag
Objects Interactions
Teacher, Student, School Bag, Pen, Teacher teaches Student.
Book Playground Student has School Bag, Book and Pen
01.4. Object-Orientation - Advantages
As Object Oriented Models map directly to reality as we have seen in examples above
therefore,
We can easily develop an object oriented model for a problem.
Everyone can easily understand an object oriented model.
We can easily implement an object oriented model for a problem using any object
oriented language like c++ using its features1 like classes, inheritance, virtual functions
and so on…
01.5. What is an Object?
An object is,
1. Something tangible (Ali, School, House, Car).
2. Something conceptual (that can be apprehended intellectually for example
time, date and so on…).
An object has,
1. State (attributes)
2. Well-defined behavior (operations)
1
We will study these features in detail in this course
3. Unique identity
01.6. Tangible and Intangible Objects
Examples of Tangible Objects:
Ali is a tangible object, having some characteristics (attributes) and behavior as given
below,
Ali
Characteristics (attributes) Behaviour (operations)
Name Walks
Age Eats
We will identify Ali using his name.
Car is also a tangible object having some characteristics (attributes) and behavior
given below,
Car
State (attributes) Behavior (operations)
Color Accelerate
Model Start Car
Change Gear
We can identify Car using its registration number
Examples of Intangible Objects (also called as conceptual objects):
Time is an intangible (conceptual) object
Time
State (attributes) Behavior (operations)
Hours Set/Get Hours
Seconds Set/Get Seconds
Minutes Set/Get Minutes
We will assign our own generated unique ID in the model for Time object
Date is also an intangible (conceptual) object
State (attributes) Behavior (operations)
Year Set/Get Year
Day Set/Get Day
Month Set/Get Month
We will assign our own generated unique ID in the model for Date object.
01.7. Summary:
Model is the abstraction of some real word scenario. It helps us to understand
that scenario.
Object oriented model of any scenario (problem) describes that scenario
(problem) in the form of interacting objects.
We use Object Orientation because it helps us in mapping real world problem
in a programming language.
Object Orientation is achieved using objects and their relationships.
Properties of an object are described using its data members and behavior of an
object is described using its functions.
Objects may be tangible (physical) or intangible (also called conceptual or
virtual).
Generally when we have given a certain problem description, nouns in that
problem description are candidates for becoming objects of our system.
There may be more than one aspects of an object
It is not necessary that every object has a specific role in implementation of a
problem there may be some objects without any role, like school parking in our
school.
It is easier to develop programs using Object Oriented Programming because
it is closer to real life.
Lecture No.02
Lecture Contents
1. Information Hiding
2. Encapsulation
3. Interface
4. Implementation
5. Separation of Interface & Implementation
6. Messages
02.1. Information Hiding:
Information hiding is one of the most important principles of OOP inspired from real life
which says that all information should not be accessible to all persons. Private
information should only be accessible to its owner.
By Information Hiding we mean “Showing only those details to the outside world which
are necessary for the outside world and hiding all other details from the outside world.”
Real Life Examples of Information Hiding
1. Ali’s name and other personal information is stored in his brain we can’t access
this information directly. For getting this information we need to ask Ali about
it and it will be up to Ali how much details he would like to share with us.
2. An email server may have account information of millions of people but it will
share only our account information with us if we request it to send anyone else
accounts information our request will be refused.
3. A phone SIM card may store several phone numbers but we can’t read the
numbers directly from the SIM card rather phone-set reads this information
for us and if the owner of this phone has not allowed others to see the numbers
saved in this phone we will not be able to see those phone numbers using phone.
In object oriented programming approach we have objects with their attributes and
behaviors that are hidden from other classes, so we can say that object oriented
programming follows the principle of information hiding.
In the perspective of Object Oriented Programming Information Hiding is,
“Hiding the object details (state and behavior) from the users”
Here by users we mean “an object” of another class that is calling functions of
this class using the reference of this class object or it may be some other program
in which we are using this class.
Information Hiding is achieved in Object Oriented Programming using the
following principles,
All information related to an object is stored within the object
It is hidden from the outside world
It can only be manipulated by the object itself
Advantages of Information Hiding
Following are two major advantages of information hiding,
It simplifies our Object Oriented Model:
As we saw earlier that our object oriented model only had objects and their interactions
hiding implementation details so it makes it easier for everyone to understand our
object oriented model.
It is a barrier against change propagation
As implementation of functions is limited to our class and we have only given the name
of functions to user along with description of parameters so if we change
implementation of function it doesn’t affect the object oriented model.
We can achieve information hiding using Encapsulation and Abstraction, so we see
these two concepts in detail now,
02.2. Encapsulation
Encapsulation means “we have enclosed all the characteristics of an object in the object
itself”
Encapsulation and information hiding are much related concepts (information
hiding is achieved using Encapsulation)
We have seen in previous lecture that object characteristics include data members
and behavior of the object in the form of functions.
So we can say that Data and Behavior are tightly coupled inside an object and
both the information structure and implementation details of its operations are
hidden from the outer world.
Examples of Encapsulation
Consider the same example of object Ali of previous lecture we described it as
follows,
Ali
Characteristics
(attributes)
Name
Age
Behavior
(operations)
Walks
Eats
You can see that Ali stores his personal information in itself and its behavior is
also implemented in it.
Now it is up to object Ali whether he wants to share that information with outside
world or not. Same thing stands for its behavior if some other object inreal life
wants to use his behavior of walking it can not use it without the permission of Ali.
So we say that attributes and behavior of Ali are encapsulated in it.
Any other object don’t know about these things unless Ali share this information
with that object through an interface,
Same concept also applies to phone which has some data and behavior of showing
that data to user we can only access the information stored in the phoneif phone
interface allow us to do so.
Advantages of Encapsulation
The following are the main advantages of Encapsulation,
a. Simplicity and clarity
As all data and functions are stored in the objects so there is no data or function
around in program that is not part of any object and is this way it becomes very easy
to understand the purpose of each data member and function in an object.
b. Low complexity
As data members and functions are hidden in objects and each object has a
specific behavior so there is less complexity in code there will be no such
situations that a functions is using some other function and that functions is
using some other function.
c. Better understanding
Everyone will be able to understand whole scenario by simple looking into object
diagrams without any issue as each object has specific role and specific relation with
other objects.
Output :
Area = 30
// Java program to demonstrate encapsulation
class Encapsulate {
// private variables declared
// these can only be accessed by
// public methods of class
private String geekName;
private int geekRoll;
private int geekAge;
// get method for age to access
// private variable geekAge
public int getAge() { return geekAge; }
// get method for name to access
// private variable geekName
public String getName() { return geekName; }
// get method for roll to access
// private variable geekRoll
public int getRoll() { return geekRoll; }
// set method for age to access
// private variable geekage
public void setAge(int newAge) { geekAge = newAge; }
// set method for name to access
// private variable geekName
public void setName(String newName)
{
geekName = newName;
}
// set method for roll to access
// private variable geekRoll
public void setRoll(int newRoll) { geekRoll = newRoll; }
}
public class TestEncapsulation {
public static void main(String[] args)
{
Encapsulate obj = new Encapsulate();
// setting values of the variables
obj.setName("Harsh");
obj.setAge(19);
obj.setRoll(51);
// Displaying values of the variables
System.out.println("Geek's name: " + obj.getName());
System.out.println("Geek's age: " + obj.getAge());
System.out.println("Geek's roll: " + obj.getRoll());
// Direct access of geekRoll is not possible
// due to encapsulation
// System.out.println("Geek's roll: " +
// obj.geekName);
}
}
Practice:
In this example program, we are creating a class Student and declare
variables stdName, stdRollNo, and stdId as private.
https://cisserv1.towson.edu/~cssecinj/modules/other-modules/build-the-
lab/build-the-lab-lab-module-1/encapsulation-java/
Generalization
In OO models, some classes may have common characteristics.
We extract these features into a new class and inherit original classes from this new
class. There are many objects with common characteristics in object model. The
common characteristics (attributes and behaviour) of all these objects are combined
in a single general class. Base class encapsulates the idea of commonality of derived
classes. Base class is general class representing common behaviour of all derived classes.
This concept is known as Generalization.
It reduces the redundancy and gives us reusability, using generalization our solution
becomes less complex.
In generalization there should be “Is a Kind of Relationship” (also called “Is A
relationship”) between base and child classes.
Common attributes
Color vertices
Common behaviour
Set Color, Move
Example: Student Doctor and Teacher
