introduction to object orientation[1]

8/8/2019 Introduction to Object Orientation[1]

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INTRODUCTIONINTRODUCTIONTO OBJECTTO OBJECTORIENTATIONORIENTATION


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Overview Software Development life cycle

"Programming in the Small" and "Programming in

the Large" Object Orientation

An Object Model

Objects

Classes

Inheritance

Polymorphism

Object-Oriented Design: Finding Classes and

Operations


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Definitions Object Oriented Programming (OOP is a

programming method that combines data and

instructions into a self-sufficient "object". "Object orientation provides a new paradigm for

software construction. In this new paradigm,

objects and classes are the building blocks, while

methods, messages and inheritance produce the

primary mechanisms".- Ann L. Winbald, Samuel D.

Edwards and David R. King in the book, "Object

Oriented Software".


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Definitions In an object-oriented program, objects

represent the design. Objects have two

sections, fields (instance variables) andmethods. Fields represent what an object is.Methods represent how an object is used.These fields and methods are closely tied to

the real world characteristics and use of theobject. An object is used by means of itsmethods. The following figure shows a viewof object oriented programming


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Definitions


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Software Development Life

Cycle (SDLC)

ANALYSIS

MAINTENTANCE

IMPLEMENTATION

DESIGN


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"Programming in the Small" and

"Programming in the Large"

Programming in the small

Programs are developed by a single programmer/small group of programmers.

All aspects of the project can be understood by a

single individual.

The major problem is the development of the

algorithms and data structures needed to solve

the task at hand.


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"Programming in the Small" and

"Programming in the Large"

Programming in the large

The software system is developed by a largeteam of programmers, often with considerablespecialization.

No single individual can (likely) understand all

aspects of the project. The major problem is the coordination of the

diverse aspects of the project--people andsoftware systems


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Object Orientation

Assumptions:

Describing large, complex systems as interacting objectsmake them easier to understandthan otherwise.

The behaviors of real world objects tend to be stable

over time.

The different kinds of real world objects tend to be

stable. (That is, new kinds appear slowly; old kinds

disappear slowly.)

Changes tend to be localizedto a few objects.


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An Object Model

Our object model includes four components:

objects (i.e., abstract data structures)

classes (i.e., abstract data types)

inheritance (hierarchical relationships amongADTs)

polymorphism by inheritance Encapsulation

Abstraction


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Objects

An objectis a separately identifiable entity that hasa set of operations and a state that records the

effects of the operations. That is, an object isessentially the same as an abstract data structure aswe have discussed previously.

Objects are characterized by:

state,

operations,

identity.


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Classes A class is a template for creating objects.

A class describes a collection of related objects (i.e.,instances of the classes).

Objects of the same class have common operations and acommon set of possible states.

The concept of class is closely related to the concept ofabstract data type that we discussed previously. Rem: Abstract data type is a collection of data and a set of

operations on that data A data structure is a construct within a programming language

the stores a collection of data

A class description includes definitions of

operations on objects of the class,

the possible set of states.


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Inheritance

A class D inherits from class B if D's objects form a

subset of B's objects.

Class D's objects must support all of the class B's

operations (but perhaps are carried out in a special way).

Class D may support additional operations and an

extended state (i.e., more information fields).

Class D is called a subclass or a childorderived class.

Class B is called a superclass or a parentorbase class.


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Polymorphism

The concept of polymorphism (literally "manyforms")

Polymorphism appears in several forms.

Overloading(orad hoc polymorphism)

Parametric polymorphism

denotes the use of parameterized type (or class)definitions.

Polymorphism by inheritance (sometimes calledpure polymorphism .


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Encapsulation

Encapsulation a way of packaging

information. Encapsulation allows the programmer to present clearly specified

interfaces around the services they provide.

The programmer can decide what should be

hidden and what is intended to be visible.


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Abstraction

Abstraction refers to the act of representingessential features without including the background

details or explanations. It is the art of concentratingon the essential and ignoring the non-essential.Classes that use the concept of data abstraction areknown as "abstract data types". Abstract data types

are achieved by making certain variables andmethods in a class private.


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Object-Oriented Design:

Finding Classes and Operations

The goals of the design phase are to:

yIdentify the classes. (What kinds of objects do

we have?)

y Identify the functionality of each class. What

does each kind of object do

y Identify the relationships among the classes.Does one kind of object use another in some

way? Is it a special case of another kind?


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Example

y Computerized Telephone Book

As an example, consider a computerized telephone bookfor a university. The telephone book should containentries for each person in the university community--student, professor, and staff member. Users of the

directory can look up entries. In addition, theadministrator of the telephone book can, after supplyinga password, insert new entries, delete existing entries,modify existing entries, print the telephone book, and

print a listing of all students or of all faculty.


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1.Identify the candidate classes. List the nouns and

noun phrases from the specification:

computerized telephone book, university, telephone

book, entry, person, university community, student,

professor, staff member, employee, user,

administrator, passwordOthers implicit : name, address, menu, collection of

address


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2.Identify the candidate operations. List the

verbs from the specification.lookup entry, supply password, insert newentry, delete existing entry, modi fy existingentry, print telephone book, pr int all

students, print all employees, set telephonenumber f ield, get telephone number f ield,compare entries.


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3. Eliminate unnecessary and synonym classes

and operations.

For example, computerized telephone book, telephone

book, and directory can be combined into a singlePhoneBook class. Similarly, entry and person can

be combined into a single Person class. Inaddition, all the print operations probably probablybe combined into a single print operation with

the differing functionalities specified by parameters


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4.Associate the operations with the

appropriate classes.For example, associate lookup, insert,

delete, and modify entry operations with

the PhoneBook class, associate compare,

setPhoneNumber and

getPhoneNumber with the Person class,

etc.


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Object-Oriented Design: Finding

Relationships Among Classes

The three relationships that are common are:

y use or awareness (uses),y aggregation or containment (has-a),

y inheritance or specialization (is-a).


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Why is OOP Popular?

y OOP is revolutionary idea, totally unlikeanything that has come before programming

y OOP is an evolutionary step, followingnaturally on the heel of earlier programmingabstractions.

y People hoped that it would quickly and easilylead to increased productivity and improved

reliability - solve software crises

y People hoped for easy transition from existinglanguages

y Resonant similarity to techniques of thinkingabout problems in other domains.


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Design Issues for OOPLs

The Exclusivity of Objects

Are Subclasses Subtypes?

Implementation and Interface Inheritance

Type Checking and Polymorphism

Single and Multiple Inheritance

Allocation and Deallocation of Objects

Dynamic and Static Binding


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Objects Vs. Objects

#include

#include

class employee

{

char Fname[15],Mname[15],EMPID[6];

char Married[2];// Either Yes or NO

int age;

float Bsalary;

public:

void getdetails(); // function to get the epmloyees details

void showdetails();

float newsalary();

};


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Objects Vs. Objects

void employee::getdetails()// function get details of the general employee

{

coutFname;coutMname;

coutage;

coutMarried;

coutBsalary;

}


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Objects

void employee::showdetails() {

cout


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Objects Vs. Objects

//The Driver Program void main()

{

employee E;

E.getdetails();

cout


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Inheritance hierarchy

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