1. OOP an Introduction

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STG Intl. Ltd.1.1Rel. Feb. 2000

Object-oriented Programming An Introduction

Snapshots

Object- oriented programming An Introduction

What is an Object?

Encapsulation

The Benefits of Encapsulation

What Are Messages?

The Benefits of Messages

What are Classes?

The Term "Object"

The Benefits of Classes


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What is Inheritance? Abstraction

Polymorphism

Dynamic Binding

Overloading

Overriding

Benefits of OOPS


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Objectives

After studying this chapter, the students should be able to:

Understand the concepts of Object Oriented Methodology Abstraction, Encapsulation, Objects, Classes andInheritance.

Object- Oriented Programming

An Introduction

Object-Oriented Programming (OOP) has been developed,based on real life itself, to easily and efficiently remove theproblems associated with procedural programming.

The first achievement of OOP towards better design andmaintenance is the removal of ambiguity,

OOP handles is the problem of non-flexibility of code.


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What is an Object?

Objects are software bundles of data and related procedures.The following illustration is a common visual representation of asoftware object:

An Object


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Encapsulation

Your Bicycle


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Encapsulating related variables and methods into a neatsoftware bundle is a simple yet powerful idea that provides twoprimary benefits to software developers:

Modularity

Information hiding

What Are Messages?

Software objects interact and communicate with each other by

sending messagesto each other. When object A wants object Bto perform one of its methods, object A sends a message toobject B.

The Benefits of Encapsulation


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Messaging


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A Message with Parameters


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Three components comprise a message:

the object to whom the message is addressed (bicycle)

the name of the method to be performed (changing gears)any parameters needed by the method (to a higher gear)

The Benefits of Messages

Everything an object can do is expressed through its

methods, so message passing supports all possibleinteractions between objects.

Objects don't need to be in the same process or even on thesame machine to send and receive messages back and forth

to each other.What are Classes?

A class is a blueprint or prototype that defines the variables andthe methods common to all objects of a certain kind.


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A Class


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The Bicycle Class


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In the real world its obvious that classes are not themselves theobjects that they describe.

Then also occurs because many people use the term object

inconsistently and use it to refer to both classes and instances.The main difference between a class and an object is thatobjects are tangible, but a class is always intangible. You cantsee a class but you can always see an object.

The Benefits of ClassesObjects provide the benefit of modularity and information hiding.Classes provide the benefit of reusability

The Term "Object"


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What is Inheritance?

Classes inherit state and behavior from their superclass.

Inheritance provides a very helpful concept of code reusability.

Hierarchy of Classes


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Subclasses provide specialized behaviors from the basis ofcommon elements provided by the superclass. Through theuse of inheritance, programmers can reuse the code in thesuperclass many times.

Programmers can implement superclasses that define

"generic" behaviors (called abstract classes). The essence ofthe superclass is defined and may be partially implementedbut much of the class is left undefined and unimplemented.Other programmers fill in the details with specializedsubclasses.

Abstraction

In java, classes are used to categorize data in order to model reallife systems. Abstraction is this process of categorizing data.

The Benefits of Inheritance


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Abstraction


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Polymorphism

Polymorphism may be defined as the ability of related objects to

respond to the same message with different, but appropriate,actions.

ShapeDraw ( )

BoxObject

Draw (box )CircleObject

Draw (circle )TriangleObject

Draw (triangle )

Polymorphism


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Dynamic Binding

Binding refers to the linking of a procedure call to the codeto be executed in response to the call.

Dynamic binding means that the code associated with agiven procedure call is not known until the time of the call at

run-time. It is associated with polymorphism and inheritance.

Overloading

In Object Oriented Programming if a method depending onsome information does different job at different times thatmethod is overloaded .Overloading is nothing but a kind ofpolymorphism.


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Example:

Suppose drawGraph() is a mechanism to draw a graph

depending on the information provided,

DrawGraph():

DrawGraph(point1, point2)

DrawGraph(point1,point2,p

oint3,point4)

Draws a point at any random

location.Draws a line from point1 topoint2Draw a rectangle using thesepoints.


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Inheritance is a mechanism of inheriting the traits of parents but

some times some properties should be modified according tothe need like a son inherits legs from his parents but his walkingstyle is different. This is Overriding.

It is again a kind of polymorphism and very important in terms

of dynamic decisions.

Benefits of OOP

Through inheritance, we can eliminate redundant code andextend the use of existing classes.

Overriding

We can build programs from the standard working modules,which communicate with one another, rather than having tostart writing the code from scratch. This leads to saving ofdevelopment time and higher productivity.


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The principle of data hiding helps the programmer to buildsecure programs that cannot be invaded by code in otherparts of the program.

It is possible to have multiple instances of an object to co-exist without any interference.

It is possible to map objects in the problem domain to

corresponding objects in the program. It is easy to partition the work in a project based on objects. The data-centered design approach enables us to capture

more details of a model in implementable form. Object-oriented systems can be easily upgraded from small to

large systems. Message passing techniques for communication between

objects makes the interface descriptions with externalsystems much simpler.

Software complexity can be easily managed.

1. OOP an Introduction

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