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, Object Oriented Programming
The term Object Oriented programming is frequently heard in the programming arena.
Object oriented approach was started to overcome the limitations of the earlier
programming approaches. It is popularly known by its acronym OOP. It is used to
develop reliable and reusable software.
The programming technology is continuously developing since the start of the computer
and related technologies. New tools and techniques are included in programming in each
phase of their development. Such enhancements increased complexity in programming
and design of large software. Similarly, the users' requirements change and increase after
the software is brought into operation. The software may need maintenance and
enhancements after the regular feedback from the users. There could be problems to
represent real life entities of problem while analyzing and designing system. While
improving the software work may need to begin from the scratch that may increase
software cost too. To incorporate users' demands and enhancements in software with such
complex systems was difficult. To overcome such problems software developers were
forced to develop new programming method. OOP was introduced to solve such
programming problems.
1.1 Software Evolution
The software evolution occurred in several phases. Since the beginning of the first
computer, programming for the computer started to develop software. The earlier
electronic computer ENIAC was programmed in machine language by using switches to
enter 1 and 0.
1.2 Basic of Object Oriented Programming
Objects are the entities that can be uniquely identified from others. They have their
unique identity and found everywhere. In real world system everything exists in the form
of objects. For example desk, bench, blackboard, student, teacher, car, tree are objects.
Every object has two things, firstly its properties we call attributes and second its
behavior we call function. For example a car is an object. It has attributes like color,
number of seats, chassis number, engine number etc and behavior like move, stop,
accelerate, turn etc. The Object Oriented Programming is developed to model such real
world system. Its sole objective is to overcome the limitation of Procedure Oriented
approach. Before discussing various features of Object Oriented Programming, it is wise
to discuss characteristics of Procedure Programming and its limitations.
1.2.1 Procedure Oriented Programming
In procedure oriented programming a large program is broken down into smaller
manageable parts called procedures or functions. In procedure oriented programming
priority is given on function rather than data.
In procedure oriented programming language, a program basically consists of sequence
of instructions each of which tells the computer to do something such as reading inputs
from the user, doing necessary calculation, displaying output. When a program becomes
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,larger, it is then broken into smaller units called procedure or functions. A number of
functions are supposed to be written to accomplish such tasks. The primary focus of
procedural oriented programming is on functions rather than data. These functions do not
let code duplication. This technique is only suitable for medium sized software
applications.
The procedure oriented programming can be diagrammatically represented as follows:
In procedure oriented programming two types of data local and global are used. Data
within the function are called local data and the data which are not within any function
are called global data. Global data are accessible to the only function where it is declared.
So each function may access its local data as well as global data. The local data of one
function is not accessible to other functions. If any data is to be accessed by two or more
functions it should be made global. However, global data are vulnerable to another
programmer to be changed unknowingly. Functions are action oriented and do not
correspond to the element of the problem. The separate arrangement of data and functions
does a poor job of modeling things in the real world. That’s why procedure oriented
programming approach does not model real world system perfectly.
High Level Programming Languages like COBOL, FORTRAN, Pascal, C are
common procedure oriented programming languages.
Characteristics of POP
The characteristics of procedure oriented programming are listed as follows:
A large program is broken down into small manageable procedures or functions.
Procedure oriented programming focuses on procedure or function rather than
data.
For sharing a common data among different functions the data is made global.
Since global data are transferred from function to function; during the course of
transformation the global data may be altered by the function.
The program design of procedure oriented programming follows top down
methodology.
Limitation of POP
Even though procedure oriented programming approach is still used in software industry
it has following limitations.
Focus on functions rather than data.
In large program, it is difficult to identify belonging of global data.
The use of global data is error prone and it could be an obstacle in code
maintenance and enhancements.
The modification of global data requires the modification of those functions using
it.
Maintaining and enhancing program code is still difficult because of global data.
It does not model real world problem very well. Since functions are action
oriented and do not really correspond to the elements of problem.
Object oriented programming (OOPS)
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, The errors faced in the procedure oriented programming approach are the motivating
factor in the invention of objected oriented approach. In OOP, data are treated as a
critical element in the program and restricts freely transformation of data around the
system. Instead, data are associated with functions that operate on it and protect it from
accidental modification outside functions. OOP approach permits decomposition of a
problem into entities called objects and then build data and function around them. Data of
an object are accessible only by the function belonging with the object. But function of
one object may access the function of another object.
Object-Oriented programming is a programming methodology that associates data
structures with a set of operators which act upon it. In OOP, an instance of such an entity
is known as object. In other words, OOP is a method of implementation in which
programs are organized as co-operative collections of objects, each of which represents
an instance of some class and whose classes are all members of a hierarchy of classes
united through the property called inheritance.
Characteristics of OOPs
OOP is most sophisticated programming methodology among other methodologies by
far. Some noticeable characteristics of OOP are as follows:
Emphasis is on data rather than procedures.
Programs are divided into objects.
Function and data are tied together in a single unit.
Data can be hidden to prevent from accidental alteration from other function or
objects.
Data access is done through the visible functions so that communication between
objects is possible.
Data structures are modeled as objects.
Follows Bottom up approach of program design methodology.
Procedure oriented versus Object oriented programming
The differences between procedural and Object oriented programming are tabulated
below:
Procedure Oriented Object Oriented Programming
Programming
Emphasis is given on procedures. Emphasis is given on data.
Programs are divided into Programs are divided into objects.
functions.
Follow top-down approach of Follow bottom-up approach of
program design. program design.
Generally data cannot be hidden. Data can be hidden, so that non-
member function cannot access
them.
It does not model the real world It models the real world problem
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