important basic concept in object oriented

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Important basic concept in object oriented

Programming

Introduction

Object-oriented programming (OOP) is a programming

language model organized around "objects" rather than

"actions" and data rather than logic. Historically, a program

has been viewed as a logical procedure that takes input data,

processes it, and produces output data.

The programming challenge was seen as how to write the logic,

not how to define the data. Object-oriented programming takes

the view that what we really care about are the objects we want to

manipulate rather than the logic required to manipulate them.

Examples of objects range from human beings (described by

name, address, and so forth) to buildings and floors (whose

properties can be described and managed) down to the littlewidgets on your computer desktop (such as buttons and scroll

bars).

Getting started with object-oriented programming

The first step in OOP is to identify all the objects you want to

manipulate and how they relate to each other, an exercise often

known as data modeling. Once you've identified an object, you

generalize it as a class of objects (think of Plato's concept of the"ideal" chair that stands for all chairs) and define the kind of

data it contains and any logic sequences that can manipulate it.

Each distinct logic sequence is known as a method. A real

instance of a class is called (no surprise here) an "object" or, in

some environments, an "instance of a class." The object or class
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instance is what you run in the computer. Its methods provide

computer instructions and the class object characteristics provide

relevant data. You communicate with objects - and they

communicate with each other - with well-defined interfaces

calledmessages.

The concepts and rules used in object-oriented programming

provide these important benefits:

The concept of a data class makes it possible to define

subclasses of data objects that share some or all of the main

class characteristics. Called inheritance, this property of

OOP forces a more thorough data analysis, reduces

development time, and ensures more accurate coding.

Since a class defines only the data it needs to be concerned

with, when an instance of that class (an object) is run, the

code will not be able to accidentally access other program

data. This characteristic of data hiding provides greater

system security and avoids unintended data corruption.

The definition of a class is reuseable not only by the

program for which it is initially created but also by other

object-oriented programs (and, for this reason, can be moreeasily distributed for use in networks).

The concept of data classes allows a programmer to create

any new data type that is not already defined in the

language itself.

Simula was the first object-oriented programming language.

Java, Python, C++, Visual Basic .NET and Ruby are the most

popular OOP languages today. The Java programming language

is designed especially for use in distributed applications on

corporate networks and the Internet. Ruby is used in many Web

applications. Curl, Smalltalk, Delphi and Eiffel are also

examples of object-oriented programming languages.

OOPSLA is the annual conference for Object-Oriented


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Object-Oriented Programming (OOP) is the most dramatic

innovation in software development in the last decade. It ranks

in importance with the development of the first higher-level

languages at the dawn of the computer age. Sooner or later,

every programmer will be affected by the object-oriented

approach to program design

object-oriented programming

A type ofprogrammingin whichprogrammers definenot only the data type of a data structure, but also thetypes of operations (functions) that can be applied tothe data structure. In this way, the data structurebecomes an objectthat includes both data andfunctions. In addition, programmers can createrelationships between one object and another. Forexample, objects can inherit characteristics from

other objects.One of the principal advantages of object-oriented

programming techniques over proceduralprogramming techniques is that they enableprogrammers to create modules that do not need tobe changed when a new type of object is added. A

programmer can simply create a new object thatinherits many of its features from existing objects.

This makes object-oriented programs easier tomodify.To perform object-oriented programming, one needsan object-orientedprogramming language (OOPL).Java, C++ andSmalltalkare three of the more popularlanguages, and there are also object-oriented
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programming language

A vocabulary and set of grammatical rules for instructing acomputerto perform specific tasks. The term programming

language usually refers to high-level languages, such as

BASIC, C, C++, COBOL, FORTRAN,Ada, andPascal. Each

language has a unique set ofkeywords (words that it

understands) and a specialsyntaxfor organizingprogram

instructions.

High-level programming languages, while simple compared to

human languages, are more complex than the languages thecomputer actually understands, calledmachine languages.

Each different type ofCPUhas its own unique machine

language.

Lying between machine languages and high-level languages

are languages calledassembly languages. Assembly languages

are similar to machine languages, but they are much easier to

program in because they allow aprogrammerto substitutenames for numbers. Machine languages consist of numbers

only.

Lying above high-level languages are languages calledfourth-

generation languages (usually abbreviated 4GL). 4GLs are far
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removed from machine languages and represent the class of

computer languages closest to human languages.

Regardless of what language you use, you eventually need toconvertyour program into machine language so that the

computer can understand it. There are two ways to do this:

See compile andinterpreterfor more information about these

two methods.

The question of which language is best is one that consumes alot of time and energy among computer professionals. Every

language has its strengths and weaknesses. For example,

FORTRAN is a particularly good language for processing

numericaldata, but it does not lend itself very well to

organizing large programs. Pascal is very good for writing

well-structured and readable programs, but it is not as flexible

as the C programming language. C++ embodies powerful

object-orientedfeatures, but it is complex and difficult tolearn.

The choice of which language to use depends on the type of

computer the program is to run on, what sort of program it is,

and the expertise of the programmer.

ADVANTAGES OF OOPS

Why is everyone so excited about OOP? The chief problem with

computer programs is complexity. Large programs are probably

the most complicated entities ever created by humans. Because of

this complexity, programs are prone to error, and software errors
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can be expensive and even life threatening (in air-traffic control,

for example). Object-Oriented Programming offers a new and

powerful way to cope with this complexity. Its goal is clearer,

more reliable, more easily maintained programs.

Languages and Development Platforms

Of the Object-Oriented Programming languages, C++ is by far

the most widely used. (Java, a recent addition to the field of OO

languages, lacks certain features, such as pointers, that make it

less powerful and versatile than C++.)

In past years the standards for C++ have been in a state of

evolution. This meant that each compiler vendor handled certain

details differently. However, in November 1997, the ANSI/ISO

C++ standards committee approved the final draft of what is now

known as Standard C++. (ANSI stands for American National

Standards Institute, and ISO stands for International Standards

Institute.) Standard C++ adds many new features to the

language,such as the Standard Template Library (STL). In this

book we llow Standard C++ (except for a few places which well

note as we go

The most popular development environments for C++ are

manufactured by Microsoft and Borland and run on the various

flavors of Microsoft Windows. In this book weve attempted in

ensure that all example programs run on the current versions of

both Borland and Microsoft compilers. (See Appendixes C and D

for more on these compilers.)

Object-Oriented Design

Students are frequently mystified by the process of breaking a

programming project into appropriate classes. For this reason

weve added a chapter on object-oriented design. This chapter is

placed near the end of the book, but we encourage students to


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skim it earlier to get the flavor of OOD. Of course, small

programs dont require such a formal design approach, but its

helpful to know whats involved even when designing programs

in your head. C++ is not the same as C.

Some institutions want their students to learn C before learning

C++. In our view this is a mistake. C and C++ are entirely

separate languages. Its true that their syntax is similar, and C is

actually a subset of C++. But the similarity is largely a historical

accident. In fact, the basic approach in a C++ program is

radically different from that in a C program.

C++ has overtaken C as the preferred language for serious

software development. Thus we dont believe it is necessary or

advantageous to teach C before teaching C++. Students who

dont know C are saved the time and trouble of learning C and

then learning C++, an inefficient approach. Students who

already know C may be able to skim parts of some chapters, but

they will find that a remarkable percentage of the material is

new.

Optimize Organization for OOP

We could have begun the book by teaching the procedural

concepts common to C and C++, and moved on to the new OOP

concepts once the procedural approach had been digested. That

seemed counterproductive, however, because one of our goals is

to begin true Object-Oriented Programming as quickly as

possible. Accordingly, we provide a minimum of procedural

groundwork before getting to objects in Chapter 7. Even the

initial chapters are heavily steeped in C++, as opposed to C,

usage.

We introduce some concepts earlier than is traditional in books

on C. For example, structures are a key feature for

understanding C++ because classes are syntactically an


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extension of structures. For this reason, we introduce structures

in Chapter 5 so that they will be familiar when we discuss

classes.

Some concepts, such as pointers, are introduced later than intraditional C books. Its not necessary to understand pointers to

follow the essentials of OOP, and pointers are usually a

stumbling block for C and C++ students. Therefore, we defer a

discussion of pointers until the main concepts of OOP have been

thoroughly digested.

New Concepts

OOP involves concepts that are new to programmers of

traditional languages such as Pascal, Basic, and C. These ideas,

such as classes, inheritance, and polymorphism, lie at the heart

of Object-Oriented Programming. But its easy to lose sight of

these concepts when discussing the specifics of an object-

oriented language. Many books overwhelm the reader with the

details of language features, while ignoring the reason these

features exist. This book attempts to keep an eye on the big

picture and relate the details to the larger concepts.

Basic concepts of OOPS

Basic concepts of OOPS and Structure of C++ program

In this tutorial you will learn about Objects, Classes,

Inheritance, Data Abstraction, Data Encapsulation,

Polymorphism, Overloading, Reusability.

Before starting to learn C++ it is essential that one must have a

basic knowledge of the concepts of Object oriented


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programming. Some of the important object oriented features are

namely:

Objects Classes

Friend function

Static function

Inheritance

Data Abstraction

Data Encapsulation

Polymorphism

Overloading

Reusability

In order to understand the basic concepts in C++, the

programmer must have a command of the basic terminology in

object-oriented programming. Below is a brief outline of the

concepts of Object-oriented programming languages:

Objects:

Object is the basic unit of object-oriented programming. Objects

are identified by its unique name. An object represents a

particular instance of a class. There can be more than one

instance of an object. Each instance of an object can hold its

own relevant data.


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form Properties of the Car class and the associated actions i.e.,

object functions like Start, Move, Stop form the Methods of Car

Class.

No memory is allocated when a class is created. Memory is

allocated only when an object is created, i.e., when an instance

of a class is created.

Friend Function

C++ Friend Functions

In this C++ tutorials, you will learn about friend functions, need

for friend function, how to define and use friend function and

few important points regarding friend function, explained with

example.

Need for Friend Function:

As discussed in the earlier sections on access specifiers, when a

data is declared as private inside a class, then it is not accessible

from outside the class. A function that is not a member or an

external class will not be able to access the private data. A

programmer may have a situation where he or she would need to

access private data from non-member functions and external

classes. For handling such cases, the concept of Friend

functions is a useful tool.


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What is a Friend Function?

A friend function is used for accessing the non-public members

of a class. A class can allow non-member functions and other

classes to access its own private data, by making them friends.Thus, a friend function is an ordinary function or a member of

another class.

How to define and use Friend Function :

The friend function is written as any other normal function,

except the function declaration of these functions is precededwith the keyword friend. The friend function must have the class

to which it is declared as friend passed to it in argument.

Features of friend function

The keyword friend is placed only in thefunction declaration of the friendfunction and not in the functiondefinition.. It is possible to declare a function asfriend in any number of classes.. When a class is declared as a friend, thefriend class has access to the private

data of the class that made this a friend.. A friend function, even though it is nota member function, would have the rightsto access the private members of the


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class.. It is possible to declare the friendfunction as either private or public.

. The function can be invoked without theuse of an object. The friend function hasits argument as objects, seen in example

below.

Static Functions

Static Functions

Static member functions have a class scope and they do not have

access to the 'this' pointer of the class. When a member is

declared as static, a static member of class, it has only one data

for the entire class even though there are many objects created

for the class. The main usage of static function is when the

programmer wants to have a function which is accessible even

when the class is not instantiated.

Accessing Static Function:

A normal member function is accessed using the object and an

operator called the dot member access operator. The functions

declared static or static functions are accessed using only the

class name and the scope resolution operator, unlike in normal

member functions where these are not used.

Defining Static Function:

Static function is defined by using the keyword static before the

member function that is to be declared as static function.


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General syntax:

static return_data_type fucntionname()//Static function defined with keyword static{statement1;

//Statements for execution inside static functionstatement2;....................

}

For example if a function exforsysreturning nothing is to be declared asstaic function it is done as follows:

static void exforsys(){........;.......;}

Features of static member functions:

A static member function can only accessstatic member data, static member functions

and data and functions outside the class. The


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programmer must take note not to use staticmember function in the same manner as non- static member function, as non-static

member function can access all of the aboveincluding the static data member.

.

A non-static member function can bedeclared as virtual but care must be takennot to declare a static member function as

virtual..

The programmer must first understand theconcept of static data while learning thecontext of static functions. It is possible todeclare a data member of a class as static

irrespective of it being a public or a privatetype in class definition. If a data is declared

as static, then the static data is created andinitialized only once. Non-static data

members are created again and again. Foreach separate object of the class, the static

data is created and initialized only once. Asin the concept of static data, all objects of

the class in static functions share thevariables. This applies to all objects of theclass..

A non-static member function can be calledonly after instantiating the class as an

object. This is not the case with staticmember functions. A static member functioncan be called, even when a class is not


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instantiated..

A static member function cannot have

access to the 'this' pointer of the class.

Inheritance:

Inheritance is the process of forming a new class from an

existing class orbase class. The base class is also known

as parent class or super class , The new class that is

formed is calledderived class. Derived class is also known

as a child class orsub class.Inheritance helps in reducingthe overall code size of the program, which is an important

concept in object-oriented programming

Inheritance is the process by which new classes calledderived

classes are created from existing classes calledbase classes. The

derived classes have all the features of the base class and the

programmer can choose to add new features specific to the newly

created derived class.

For example, a programmer can create a base class named

fruit and define derived classes asmango, orange,banana, etc. Each of these derived classes, (mango,orange,banana, etc.) has all the features of the base class(fruit) with additional attributes or features specific to thesenewly created derived classes.Mangowould have its own defined

features, orange would have its own defined features,bananawould have its own defined features, etc.


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This concept of Inheritance leads to the concept of

polymorphism.

Features or Advantages of Inheritance:

Reusability:

Inheritance helps the code to be reused in many situations. The

base class is defined and once it is compiled, it need not be

reworked. Using the concept of inheritance, the programmer can

create as many derived classes from the base class as neededwhile adding specific features to each derived class as needed.

Saves Time and Effort:

The above concept of reusability achieved by inheritance saves

the programmer time and effort. Since the main code written can

be reused in various situations as needed.

Increases Program Structure which results in greater reliability.

Polymorphism (to be discussed in detail in later sections)


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General Format for implementing the conceptof Inheritance:

class derived_classname: access specifier

baseclassname

For example, if the base class is exforsys and the derived class is

sample it is specified as:

class sample: public exforsys

The above makes sample have access to both public and

protected variables of base class exforsys . Reminder about

public, private and protected access specifiers:

If a member or variables defined in aclass is private, then they are accessible

by members of the same class only andcannot be accessed from outside the class.

. Public members and variables are

accessible from outside the class.. Protected access specifier is a stage

between private and public. If a memberfunctions or variables defined in a classare protected, then they cannot be


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accessed from outside the class but can beaccessed from the derived class.

Inheritance Example:

class exforsys{

public:exforsys(void) { x=0; }void f(int n1){x= n1*5;}

void output(void) { cout


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exforsys::output();cout


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the derived class sample has new member function f1( ) added in

it. The line:

sample s;

creates a derived class object named as s. When this is created,

space is allocated for the data members inherited from the base

class exforsys and space is additionally allocated for the data

members defined in the derived class sample.

The base class constructorexforsys is used to initialize the base class data members

and the derived class constructor sample is used to initialize the data members

defined in derived class.

The access specifier specified in the line:

class sample: public exforsys

Public indicates that the public data members which are inherited from the base class

by the derived class sample remains public in the derived class.

Data Abstraction:

Data Abstraction increases the power of programming language

by creating user defined data types. Data Abstraction also


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represents the needed information in the program without

presenting the details.

Data Encapsulation:

Data Encapsulation combines data and functions into a single

unit called Class. When using Data Encapsulation, data is not

accessed directly; it is only accessible through the functions

present inside the class. Data Encapsulation enables the

important concept of data hiding possible.

Polymorphism:

Polymorphism allows routines to use variables of different types

at different times. An operator or function can be given different

meanings or functions. Polymorphism refers to a single function

or multi-functioning operator performing in different ways.

Overloading:

Overloading is one type of Polymorphism. It allows an object to

have different meanings, depending on its context. When an

exiting operator or function begins to operate on new data type,

or class, it is understood to be overloaded.

Reusability:

This term refers to the ability for multiple programmers to use

the same written and debugged existing class of data. This is a

time saving device and adds code efficiency to the language.


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Additionally, the programmer can incorporate new features to

the existing class, further developing the application and

allowing users to achieve increased performance. This time

saving feature optimizes code, helps in gaining secured

applications and facilitates easier maintenance on theapplication.

The implementation of each of the above object-oriented

programming features for C++ will be highlighted in later

sections.

A sample program to understand the basic structure of C++

//program to read employee details and tooutput the data#include Preprocessor directive

classemployee Class Declaration{

private:char empname[50];int empno;

public:

void getvalue(){

coutempname;coutempno;


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}

void displayvalue(){

cout


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included placed between < >..

The next structure present in the program

is the class definition. This starts with thekeyword class followed by class name

employee. Within the class are data andfunctions. The data defined in the class are generally private and functions are public.These explanations we will be detailed in

later sections. The class declaration endswith a semicolon.

.

main() function is present in all C++programs..

An object e1 is created in employee class.Using this e1 the functions present in the

employee class are accessed and there bydata are accessed.

. The input namely ename and eno is got

using the input statement namely cin and thevalues are outputted using the output

statement namely cout.

important basic concept in object oriented

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