1 intro

SHARDA UNIVERSITY
“OOPs Using Java ”
Unit-I
Introduction

What is programming?
Programming is taking
A problem
Find the area of a rectangle
A set of data
length
width
A set of functions
area = length * width
Then,
Applying functions to data to solve the
problem
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Programming Paradigm
 Procedural Programming Language (PPL)
 Object Oriented Programming (OOP)
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Procedural Programming
The main program coordinates calls to procedures
and hands over appropriate data as parameters.
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Procedural Concept
 Procedural Languages
 C, Pascal, Basic, Fortran
 Facilities to
 Pass arguments to functions
 Return values from functions
 For the rectangle problem, we develop a function
int compute_area (int l, int w){
return ( l * w );
}
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Object-Oriented Concept
 Objects of the program interact by sending messages
to each other
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Objects
An object is an encapsulation of both functions and data.
 Objects are an Abstraction
 represent real world entities
 Classes are data types that define shared common properties or
attributes
 Objects are instances of a class
 Objects have State
 have a value at a particular time
 Objects have Operations
 associated set of operations called methods that describe how to
carry out operations
 Objects have Messages
 request an object to carry out one of its operations by sending it a
message
 messages are the means by which we exchange data between
objects 7

Object as an Instance
 Instance refers to the copy of the object at a
particular time whereas object refers to the memory
address of the class.
 Object is instance of a Class.
 Instance means just creating a reference(copy) of an
object.
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Cont…
 Class A {}
A obj1; //this is the object declaration without
occupy any memory.
A obj2 = new A(); //this is the object instance with
occupy memory for this.
also we can't create an instance for abstract class as
well as for interface.
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Object Oriented Programming
 Object Oriented Programming (OOP) is a programming
paradigm that uses “Objects”
– data structures consisting of data fields and methods
together with their interactions
- to design applications and computer programs.
 An object is actually a discrete bundle of functions and
procedures, all related to a particular real-world concept.
 OOP focuses on data rather than processes, with programs
composed of self-sufficient modules (objects) each
containing all the information needed to manipulate its
own data structure.
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Cont…
 In OOP, each object is capable of receiving messages,
processing data, and sending messages to other objects and
can be viewed as an independent ‘machine’ with a distinct
role or responsibility.
 The Simula67 programming language was the first to
introduce the concepts underlying OOP.
 Smalltalk was the first programming language to be called
“object-oriented”.
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OOP vs. PPL
 OOL is concerned to develop an application based on real
time while PPL are more concerned with the processing of
procedures and functions.
 In OOL, more emphasis is given on data rather than
procedures, while the programs are divided into objects
and the data is encapsulated from the external
environment, providing more security to data which is not
applicable or rather possible in PPL.
 In OOL, the objects communicate with each other via
functions while there is no communication in PPL rather
it’s simply a passing values to the arguments to the
functions and/or procedures.
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OOP vs. PPL
 OOL follows bottom up approach or program
execution while in PPL its top down approach.
 OOP languages :- JAVA, VB.Net, C#.Net
PPL Languages :- C, VB, Perl, Basic, Fortran
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Design Methodology
 Functional decomposition (Top-Down)
 The whole system is characterized by a single function,
and then the function is decomposed into a set of
functions in a process of stepwise refinement.
 Functional composition (bottom-up)
 You can have different components of functions such as
that from a function library
 You can compose them into a module with a more
significant function.
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OOL Languages
 Pure OO languages-
 Everything in them is treated consistently as an object,
from primitives such as characters and punctuation, all
the way up to whole classes, prototypes, blocks,
modules,etc.
 Designed specifically to facilitate, even enforce, OO
methods.
 Examples : Smalltalk, Eiffel, Ruby, JADE
 Languages designed mainly for OO
programming, but with some procedural
elements.
 Examples : C++ , JAVA, Python
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OOL Languages
 Languages that are historically procedural languages,
but have been extended with some OO features.
 Examples : Fortran 2003, Perl, COBOL 2002, PHP.
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CONCEPTS OF OOP
The concept of object oriented programming is categorized into the
following elements:
1. Class & Object.
2. Encapsulation.
3. Abstraction.
4. Data hiding.
5. Polymorphism.
6. Inheritance.
7. Dynamic Binding.
8. Message Passing.
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CLASS & OBJECT
 A class is a collection of function code and data which forms
the basis of object oriented programming.
 A class is an Abstract Data type (ADT) i.e. the class definition
only provides the logical abstraction.
 The data and function defined within the class spring to life
only when a variable of type class is created.
 The variable of type class is called an objects which has a
physical existence and also known as an instance of a class.
 From one class several objects can be created.
 A class is termed as a basic unit of encapsulation.
 Each objects has similar set of data defined in the class and it
can use functions defined in the class for the manipulation of
data.
 For example we can create a class Car which have properties
like company model, year of manufacture, fuel type etc which
may have actions like accelerate ( ), brake( ) etc.
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CLASS & OBJECT CONT.
 Objects are the basic entity in a C++ program.
 All objects are instances of a class. Depending upon type of class an
object may represented any thing like a person, mobile, chair, student,
employee, book, lecturer, speaker etc.
 The state of an object is determined by the data values they are having
at a particular instance.
 Objects occupy space in memory and all objects share same set of data
items which are defined when class is created.
 Two objects may communicate with each other through functions by
passing messages.
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ENCAPSULATION
 Encapsulation is the mechanism that binds together function and data
in one compact form known as class.
 The data and function may be private or public.
 Private data/ function can only be accessed only with in the class.
 Public data/code can be accessed outside the class.
 The use of encapsulation hides complexity from the implementation.
 Linking of function code and data together gives rise to objects which
are variables of type class.
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ABSTRACTION
 Abstraction is a mechnism to represent only essential features which are
of significance and hides the unimportant details.
 To make a good abstraction we require a sound knowledge of the problem
domain which we are going to implement using OOP principles.
 As an example of abstraction consider a class Vehicle. When we create the
vehicle class, we can decide what function code and data to put in the
class like vehicle name, no. of wheels, fuel type, vehicle type etc. and
functions like changing the gear, accelerating/ decelerating the vehicle. At
this time we are not interested how vehicle works like how acceleration,
changing gear take place. We are also not interested in making more parts
of vehicle to be part of the class like model number, vehicle color etc.
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DATA HIDING
 Data hiding hides the data from external access by the user.
 In OOP language we have special keywords like private and protected
etc. which hides the data.
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POLYMORPHISM
If we bi-furcate the words Polymorphism we get:
POLY Many
MORPHISM Form
1. Thus polymorphism means more than one form.
2. Thus polymorphism provides a way for an entity to behave in several
form.
3. In layman’s term a excellent example of polymorphism is Lord Krishna
in Hindu methodology.
4. From programmer point of view polymorphism means “ one interface
many methods”
5. Polymorphism is of two types
a) Compile time polymorphism.
b) Run Time polymorphism.
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INHERITANCE
 Inheritance is the mechanism of deriving a new class from the earlier
existing class.
 The inheritance provides the basic idea of reusability in Object
Oriented Programming.
 The new class inherits the features of the old class.
CLASS – A (BASE CLASS)
CLASS –B (DERIVED CLASS)
Figure: Introduction of Inheritance
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DYNAMIC BINDING
 Binding means linking.
 It is linking of function definition to a function call.
 If linking of function call to function definition i.e. a place where
control has to be transferred is done at compile time, it is known
as static binding or early binding.
 When linking is delayed till run time or done during the
execution of the program then this type of linking is known as
dynamic binding.
 Which function will be called in response to a function call is find out
when program executes.
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MESSAGE PASSING
 In C++ objects communicate each other by passing messages to each
other. A message contains the name of the member function and
arguments to pass. In message passing shown as follows:
object. Method (parameters);
 Message passing here means objects calling the method and passing
parameters. Message passing is nothing but calling the method of the
class and sending parameters. The method in turn executes in response
to a message.
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CHARACTERISTICS OF OOP
 Programs are divided into classes and functions.
 Data is hidden and cannot be accessed by external
functions.
 Use of inheritance provides reusability of code.
 New functions and data items can be added easily.
 Data is given more importance than functions.
 Follows bottom-up approach.
 Data and functions are tied together in a single unit known
as class.
 Objects communicate each other by sending messages in
the form of function.
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ADVANTAGES OF OOP
 Code reusability in terms of inheritance.
 Object oriented system can be easily upgraded from one
platform to another.
 Complex projects can be easily divided into small code
functions.
 The principle of abstraction and encapsulation enables a
programmer to build secure program.
 Software complexity decreases.
 Principle of data hiding helps programmer to design and
develop safe programs.
 Rapid development of software can be done in short span
of time.
 More than one instance of same class can exist together
without any interference.
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OBJECT ORIENTED LANGUAGES
 Some of the most popular Object-Oriented programming
languages are:
1. C++
2. Java
3. Smalltalk
4. Eiffle
5. Ruby
6. Delphi
7. Charm++
8. Simula
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OBJECT-BASED LANGUAGE
 The languages which only concerns with classes and
objects and do not have features like: inheritance,
polymorphism etc are known as object based language.
 In these types of languages we can create classes and
objects and can work with them .
 They are usually having a larger numbers of built-in objects
of various types.
 Some of the languages which are object-based are:
a) Java script
b) Visual Basic.
c) Delphi etc.
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