This document provides an overview of object-oriented design concepts including classes, objects, encapsulation, inheritance, polymorphism, and persistence. It defines key terms like class, object, abstraction, and polymorphism. Examples are given of different classes like Account, Shape, Circle, and Rectangle to illustrate concepts like encapsulation, inheritance, polymorphism, and polymorphism. The benefits of object-oriented design like reusability, reliability, and ease of modeling real-world problems are also summarized.

1. Overview
Understand Classes and Objects.
Introduction to Object Oriented
Design
Understand some of the key
concepts/ features in the Object Oriented
paradigm.
Benefits of Object Oriented Design
paradigm.
1 2
OOP: model, map, reuse, extend Examples of Objects
¡
Model the real world
problem to user’s
perceive;
¡
Use similar metaphor
CAR BOY GIRL CLOCK
in computational env.
¡
Construct reusable
components;
¡
Create new
components from
VDU BOOK TREE TRIANGLE
existing ones.
Figure 1.9: Examples of objects
3 4
Classes: Objects with the same
Object Oriented Paradigm: Features
attributes and behavior
Person Objects Encapsulation
Abstract Person Class Data Abstraction
Into Attributes: Name, Age, Sex
Operations: Speak(), Listen(), Walk()
Single Inheritance
Vehicle Objects
Polymorphism
OOP
Vehicle Class
Abstract
Attributes: Name, Model, Color Paradigm
Into
Operations: Start(), Stop(), Accelerate()
Persistence
Polygon Objects Delegation
Polygon Class
Abstract Attributes: Vertices, Border,
Into Color, FillColor Genericity
Operations: Draw(), Erase(), Move()
Multiple Inheritance
Figure 1.12: Objects and classes 5 6

2. Java’s OO Features Encapsulation
Encapsulation Encapsulation
¡
It associates the code
Data Abstraction Data Abstraction and the data it
manipulates into a
Single Inheritance Single Inheritance
single unit; and
OOP
Polymorphism
OOP
Polymorphism keeps them safe from
Java
Paradigm Paradigm external interference
Persistence Persistence
and misuse.
Delegation Delegation
Genericity Genericity Data
Functions
Multiple Inheritance Multiple Inheritance
7 8
Data Abstraction Abstract Data Type (ADT)
Encapsulation
The technique of
A structure that contains both data
¢
£
Data Abstraction creating new data types
that are well suited to an and the actions to be performed on
application.
Single Inheritance
that data.
¢
It allows the creation of
Polymorphism
OOP user defined data types,
Paradigm having the properties of
Persistence
built data types and a set
£
Class is an implementation of an
of permitted operators. Abstract Data Type.
Delegation
¢
In Java, partial support.
Genericity ¢
In C+ + , fully supported
(e.g., operator
Multiple Inheritance overloading). 9 10
Class- Example Class
class Account { ¤
Class is a set of attributes and operations
private String accountName; that are performed on the attributes.
private double accountBalance;
Student Circle
public withdraw(); Account
public deposit(); accountName
accountBalance
name
age
centre
radius
studentId
public determineBalance(); withdraw() area()
deposit() getName()
} / / Class Account determineBalance() getId()
circumference()
11 12

3. Objects Classes/ Objects
John and Jill are
£
An Object Oriented system is a :John
objects of class
Student
collection of interacting Objects. Student
:Jill
£
Object is an instance of a class.
:circleA circleA and circleB
Circle are
:circleB objects of class
Circle
13 14
Class Object
¤
A class represents a template for several ¤
Objects have state and classes don’t.
John is an object (instance) of class Student.
objects that have common properties. name = “John”, age = 20, studentI d = 1236
Jill is an object (instance) of class Student.
¤
A class defines all the properties common name = “Jill”, age = 22, studentId = 2345
to the object - attributes and methods. circleA is an object (instance) of class Circle.
centre = (20,10), radius = 25
¤
A class is sometimes called the object’s circleB is an object (instance) of class Circle.
centre = (0,0), radius = 10
type.
15 16
Encapsulation Encapsulation - Example
¥
All information (attributes and methods) in an class Account {
object oriented system are stored within the private String accountName; message
object/ class. private double accountBalance;
¥
Information can be manipulated through Withdraw
Deposit
operations performed on the object/ class – public withdraw();
public deposit(); messag Account
interface to the class. Implementation is hidden e balance
from the user. public determineBalance();
¥
Object support Information Hiding – Some } / / Class Account
Determine Balance
attributes and methods can be hidden from the
user. message
17 18

4. Data Abstraction Abstraction - Example
¤
The technique of creating new data types class Account {
that are well suited to an application. private String accountName;
Creates a data
private double accountBalance;
type Account
public withdraw();
¤
I t allows the creation of user defined data public deposit(); Account acctX;
types, having the properties of built in public determineBalance();
} // Class Account
data types and more.
19 20
Inheritance Inheritance - Example
¤
New data types (classes) can be defined
¥
Example
¦
Define Person to be a class
as extensions to previously defined types. §
A Person has attributes, such as age, height, gender
Assign values to attributes when describing object
Parent Class (Super Class) – Child Class
§
¤
(Sub Class) ¦
Define student to be a subclass of Person
Parent
§
A student has all attributes of Person, plus attributes of
¤
Subclass inherits his/her own ( student no, course_enrolled)
A student has all attributes of Person, plus attributes of
properties from the
§
Inherited his/her own (student no, course_enrolled)
capability A student inherits all attributes of Person
parent class.
§
¦
Define lecturer to be a subclass of Person
§
Lecturer has all attributes of Person, plus attributes of
Child his/her own ( staff_id, subjectI D1, subjectID2)
21 22
Inheritance - Example Inheritance - Example
¤
Circle Class can be a subclass (inherited ¤
I nheritance can also have multiple levels.
from ) of a parent class - Shape Shape
Shape
Circle Rectangle
Circle Rectangle GraphicCircle
23 24

5. Uses of I nheritance - Reuse Uses of I nheritance - Reuse
Circle Rectangle
¥
If multiple classes have common centre
attributes/ methods, these methods can be centre height
radius width
moved to a common class - parent class. area() area()
circumference() circumference()
move(newCentre) move(newCentre)
¥
This allows reuse since the implementation is
not repeated.
move(newCentre){
centre = newCentre; move(newCentre){
Example : Rectangle and Circle method have a } centre = newCentre;
}
common method move(), which requires changing
the centre coordinate.
25 26
Uses of I nheritance - Reuse Uses of I nheritance - Specialization
Shape
¤
Specialized behavior can be added to the
centre move(newCentre){
centre = newCentre child class.
area() }
circumference()
move(newCentre)
¤
I n this case the behaviour will be
implemented in the child class.
¨
E.g. The implementation of area() method in
Rectangle
the Circle class is different from the
Circle
Rectangle class.
height
radius width
¤
area() method in the child classes
area() area() override the method in parent classes().
circumference() circumference()
27 28
Uses of I nheritance - Specialization Uses of I nheritance - Specialization
Shape
Circle Rectangle
centre area(); - Not implemented
centre centre And left for the child classes
height
radius width area() To implement
area() area() circumference()
circumference() circumference() move(newCentre)
move(newCentre) move(newCentre)
area(){
area(){ Circle Rectangle
return pi* r^ 2;
return pi* r^ 2; area(){
}
} return height* width;
height
} radius width
area() area(){
area()
circumference() return height* width;
circumference()
}
29 30

6. Uses of I nheritance – Common Interface Uses of I nheritance - Extension
¥
All the operations that are supported for ¤
Extend functionality of a class.
Rectangle and Circle are the same.
¥
Some methods have common implementation
¤
Child class adds new operations to the
and others don’t. parent class but does not change the
¦
move() operation is common to classes and can be
implemented in parent. inherited behavior.
¦
circumference(), area() operations are significantly
different and have to be implemented in the
respective classes. ¨
E.g. Rectangle class might have a special
¥
The Shape class provides a common interface operation that may not be meaningful to the
where all 3 operations move(), circumference() Circle class - rotate90degrees()
and area().
31 32
Uses of I nheritance - Extension Uses of I nheritance – Multiple I nheritance
Shape
¤
I nherit properties from more than one
centre
area()
class.
circumference()
move(newCentre)
¤
This is called Multiple Inheritance.
Graphics Shape
Circle Rectangle
height
radius width
area()
area()
circumference()
circumference() Circle
rotate90degrees()
33 34
Uses of Multiple Inheritance Uses of I nheritance – Multiple I nheritance
GraphicCircle Shape
¤
This is required when a class has to
centre
inherit behavior from multiple classes. color
area()
paint() circumference()
¤
I n the example Circle class can inherit move(newCentre)
move() operation from the Shape class
and the paint() operation from the
Graphics class.
Circle
¤
Multiple inheritance is not supported in
JAVA but is supported in C+ + . radius
area()
circumference()
35 36

7. Polymorphism Polymorphism
¥
Polymorphic which means “many forms” has ¥
An object of type Circle or Rectangle can be
Greek roots. assigned to a Shape object. The behavior of the
¦
Poly – many object will depend on the object passed.
¦
Morphos - forms.
circleA = new Circle(); Create a new circle object
¥
In OO paradigm polymorphism has many Shape shape = circleA;
forms. shape.area(); area() method for circle class will be executed
¥
Allow a single object, method, operator rectangleA = new Rectangle(); Create a new rectangle object
associated with different meaning depending shape= rectangle;
on the type of data passed to it. shape.area() area() method for rectangle will be executed.
37 38
Polymorphism – Method Overloading Polymorphism – Operator Overloading
¤
Multiple methods can be defined with the ¤
Allows regular operators such as + , -, * , /
same name, different input arguments. to have different meanings based on the
Method 1 - initialize(int a) type.
Method 2 - initialize(int a, int b)
¤
E.g. + operator for Circle can re-defined
¤
Appropriate method will be called based Circle c = c + 2;
on the input arguments.
initialize(2) Method 1 will be called.
¤
Not supported in JAVA. C+ + supports it.
initialize(2,4) Method 2 will be called.
39 40
Persistence Why OOP?
¤
The phenomenon where the object ¤
Greater Reliability
outlives the program execution. ¨
Break complex software projects into small,
self-contained, and modular objects
¤
Databases support this feature. ¤
Maintainability
¨
Modular objects make locating bugs easier,
with less impact on the overall project
¤
I n Java, this can be supported if users
explicitly build object persistency using I O
¤
Greater Productivity through Reuse!
streams. ¤
Faster Design and Modelling
41 42

8. Benefits of OOP.. Benefits of OOP..
¤
I nheritance: Elimination of Redundant ¤
Multiple objects to coexist without any
Code and extend the use of existing interference.
classes. ¤
Easy to map objects in problem domain
¤
Build programs from existing working to those objects in the program.
modules, rather than having to start from ¤
I t is easy to partition the work in a
scratch. Æ save development time and project based on objects.
get higher productivity. ¤
The Data-Centered Design enables us in
¤
Encapsulation: Helps in building secure capturing more details of model in an
programs. implementable form.
43 44
Benefits of OOP.. Summary
¤
Object Oriented Systems can be easily
©
Object Oriented Design, Analysis, and Programming is a
Powerful paradigm
upgraded from small to large systems. ©
Enables Easy Mapping of Real world Objects to Objects
¤
Message-Passing technique for in the Program
©
This is enabled by OO features:
communication between objects make
Encapsulation
the interface descriptions with external
Data Abstraction
Inheritance
systems much simpler.
Polymorphism
¤
Software complexity can be easily
Persistence
©
Standard OO Design (UML) and Programming
managed. Languages (C+ + / Java) are readily accessible.
45 46
Reference
¤
Chapter 1: “Programming with Java” by
Balagurusamny
¤
Optional:
¨
Chapter 1: “Mastering C+ + ” by V. Rajuk and
R. Buyya, Tata McGraw Hill, New Delhi,
India.
47