Object-Oriented Programming (OOP)

OBJECT-ORIENTED PROGRAMMING
(OOP)
Ahmad Karawash

OUTLINE
• Definitions
• Classes & Objects
• OOP concepts
• Pros & Cons
2

OBJECT-ORIENTED PROGRAMMING (OOP)
3

DEFINITION
• OOP is mainly a program design philosophy.
• Key idea: The real world can be “accurately” described as a collection of
objects that interact.
• Everything is grouped as self sustainable "objects". Hence, you gain
reusability by means of four main OOP concepts.
4
Object-Oriented Programming (OOP)

OOP BASIC TERMINOLOGY
• Object - usually a person, place or thing (a noun)
• Method - an action performed by an object (a verb)
• Property or attribute - Characteristics of certain object.
• Class - a category of similar objects (such as automobiles), does not hold
any values of the object’ s attributes/properties
5

OPERATIONS/METHODS
• In OOP, programmers define not only the data type of a data structure, but
also the types of operations/methods (functions) that can be applied to the
data structure.
• In this way, the data structure becomes an object that includes both data
and functions (methods) in one unit. In addition, programmers can create
relationships between one object and another.
• For example, objects can inherit characteristics from other objects.
6

OOP LANGUAGES
• Pure OO Languages
• Ruby, Python, Scala, JADE.
• Hybrid OO Languages
• Delphi, C++, Java, C#, VB.NET, Pascal, Visual Basic, MATLAB, Fortran, Perl,
COBOL, PHP.
7

DEFINITIONS
• A class is a prototype, idea, and blueprint for creating objects.
• For example, in Java we define classes, which in turn are used to create
objects
• A class has a constructor for creating objects
• Class is composed of three things: its name, attributes/properties, and
methods.
• Each copy of an object from a particular class is called an instance of the
class.
• The act of creating a new instance of a class is called instantiation.
9
Classes & Objects

CLASSES V.S. OBJECTS
• A class is a definition of objects with the same properties and the same
methods.
• An object is an instance of a class
10
Classes & Objects

TECHNICAL CONTRAST BETWEEN
OBJECTS & CLASSES
Object is a class in “runtime”
11
Classes & Objects

ALMOST EVERYTHING IN THE WORLD
CAN BE REPRESENTED AS AN OBJECT
• A flower, a tree, an animal
• A student, a professor
• A desk, a chair, a classroom, a building, etc.
12
Classes & Objects

IN SHORT
An Object is a Class when it comes alive!
• Homo Sapien is a class, John and Jack are objects
• Animal is a class, the cat is an object
• Vehicle is a class, my neighbor's BMW is an object
• Galaxy is a class, the MilkyWay is an object
13
Classes & Objects

OBJECTS NEED TO COLLABORATE!
• Objects are useless unless they can collaborate to solve a problem.
• Each object is responsible for its own behavior and status.
• No one object can carry out every responsibility on its own.
14
Classes & Objects

HOW DO OBJECTS INTERACT WITH
EACH OTHER?
15
Classes & Objects

EXAMPLE OF OBJECT
INTERACTION
The OrderEntryForm wants Order to calculate the total CAD value for the
order.
16
Classes & Objects

OOP FOUR MAIN CONCEPTS
Encapsulation
Inheritance
Abstraction
Polymorphism
18
OOP Concepts

OOP CONCEPTS - ENCAPSULATION
19

ENCAPSULATION DEFINITION
• Is the inclusion of property & method within a class/object in which it needs
to function properly.
• Also, enables reusability of an instant of an already implemented class within
a new class while hiding & protecting the method and properties from the
client classes.
20
OOP concepts - Encapsulation

ENCAPSULATION WITH CLASSES
• The class is kind of a container or capsule or a cell, which encapsulate the
set of methods, attributes and properties to provide its indented
functionalities to other classes.
• In that sense, encapsulation also allows a class to change its internal
implementation without hurting the overall functioning of the system.
• That idea of encapsulation is to hide how a class does its operations while
allowing requesting its operations.
21

ENCAPSULATION IN ACTION
Example:
Let’s say we have a class called “Date” (day, month, year). And then you
need to define another class called “Person” that has the following attributes
(first name, last name, and birthdate). So in this case we can instantiate an
object from class “Date” inside class “Person”
22
Date
Person

ENCAPSULATION – BENEFITS
• Ensures that structural changes remain local:
• Changing the class internals does not affect any code outside of the class
• Changing methods' implementation does not reflect the clients using them
• Encapsulation allows adding some logic when accessing client's data
• E.g. validation on modifying a property value
• Hiding implementation details reduces complexity -> easier maintenance
23

INHERITANCE DEFINITION
• Term comes from inheritance of traits like eye color, hair color, and so on.
• Classes with properties in common can be grouped so that their common
properties are only defined once in parent class.
• Superclass – inherit its attributes & methods to the subclass(es).
• Subclass – can inherit all its superclass attributes & methods besides having its
own unique attributes & methods.
25
OOP concepts - Inheritance

INHERITANCE PARENT/CHILD
• Inheritance allows child classes to inherit the characteristics of existing parent
class
• Attributes (fields and properties)
• Operations (methods)
• Child class can extend the parent class
• Add new fields and methods
• Redefine methods (modify existing behavior)
26

INHERITANCE BENEFITS
• Expresses commonality among classes/objects
• Allows code reusability
• Highlights relationships
• Helps in code organization
27

INHERITANCE EXAMPLE
28

EXAMPLE: SINGLE INHERITANCE
One class inherits from another.
29

EXAMPLE: MULTIPLE INHERITANCE
A class can inherit from several other classes.
Most modern languages don’t support multiple
inheritance!
30

ABSTRACTION DEFINITION
• Abstraction is a basic representation of a concept.
• It is the process of removing characteristics from something in order to
reduce it to a set of essential characteristics.
• Through the process of abstraction, a programmer hides all but the relevant
data about a class in order to reduce complexity and increase reusability.
32
OOP concepts - Abstraction

ABSTRACTION BENEFITS
• Abstraction allows programmers to represent complex real world in the
simplest manner.
• It represent the necessary features an object should possess without
representing the background details.
• It allow ease reusability and understanding for the design and enable
extension.
33

ABSTRACT CLASS
• An abstract class, which declared with the “abstract” keyword, cannot be
instantiated.
• It can only be used as a super-class for other classes that extend the
abstract class. Abstract class is a design concept and implementation gets
completed when it is being realized by a subclass.
34

TYPE OF CLASSES
Concrete Class Abstract Class
Can be instantiated directly Cannot be instantiated directly
35

ABSTRACTION + INHERITANCE
Concrete Class
Abstract Class
Can be instantiated directly
Cannot be instantiated directly
Person
Teacher Student
DOB:
Name:
Address:
Specialization:
Academic Title:
Etc…:
DOB:
Name:
Address:
GPA:
Courses:
Etc…:
DOB
Name
Address
Can be instantiated directly
36

ABSTRACT CLASS: INSTANCE &
OPERATION
• An abstract class is a class that may not have any direct instances.
• An abstract operation is an operation that it is incomplete and requires a
child to supply an implementation of the operation.
37

OOP CONCEPTS - POLYMORPHISM
38

POLYMORPHISM DEFINITION
• Polymorphisms is a generic term that means 'many shapes’.
• More precisely Polymorphisms means the ability to request that the same
methods be performed by a wide range of different types of things.
• It is achieved by using many different techniques named method
overloading, operator overloading, and method overriding.
39
OOP concepts - Polymorphism

POLYMORPHISM TRAITS
• An object has “multiple identities”, based on its class inheritance tree
• It can be used in different ways
40

POLYMORPHISM METHODS
• In Java, two or more classes could each have a method called output.
• Each output method would do the right thing for the class that it was in.
• One output might display a number (output.number) in one class, whereas it
might display a name (output.text) in another class.
41

POLYMORPHISM + ABSTRACT
CLASS EXAMPLE
Shape
method Draw()
Circle
Circle.Draw()
Triangle
Triangle.Draw()
Square
Square.Draw()
42

OOP PROS
• Code reuse & recycling
• Improved software-development productivity
• Improved software maintainability
• Faster development
• Lower cost of development
• Higher-quality software
• Encapsulation
44
Conclusion

OOP CONS
• Steep learning curve
• Could lead to larger program sizes
• Could produce slower programs
45
Conclusion

Object-Oriented Programming (OOP)

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