Object-Oriented Programming

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Object-Oriented Programming

• B.Ramamurthy

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Object-Oriented Principles
OOP
Polymorphism -- Many forms of same function --
Virtual functions -- Abstract Base Classes
Inheritance -- Hierarchy -- Reusability --
Extensibility -- Expressive power -- Reflects
many real-world problems
Encapsulation (class) -- Information Hiding --
Separation of Interface and
Implementation -- Standardization -- Access
Control mechanisms (private /public)
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Why Object-oriented paradigm?

• Separation of interface and implementation
• Any implementation change should not affect user
  interface.
• To ease design process Separation of Design
  definition, Implementation, Usage through data
  encapsulation.
• Software reuse
• To allow (1) sharing, (2) upgrades (3)
  modification using inheritance and polymorphism.
• Parameterized classes in templates.

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OO Concepts sampler

• Consider the automobile (car) you drive.
• List the behaviors (functions) of this
  automobile.
• The ones you have control over define the
  user-interface of the automobile.
• The internal behavior defines the private
  functionality. As a user you have no control over
  the implementation of these.
• List the attributes (parts) of the automobile.
• You have access to some. Example steering wheel,
  brakes, head-lights, wipers.
• You do not have access to some others Odometer

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Encapsulation class car

• class Car
• public //interface
• // behavior or functions
• startEngine
• accelerate
• brake
• park
• shiftGear
• // attributes or parts
• color
• seatBelt
• private //under the hood
• displaySpeed()
• Odometer
• Engine

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The notion of class

• Things discussed above are in general applicable
  to any car or Shall we say to a class of cars?
• Some functionality and parts are to be hidden.
• An interface containing a set of functions and
  components have to be presented to the user of
  the car.

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From problem to OO solution

• Identify the objects (nouns) in the problem.
• Define and implement classes to represent the
  objects.
• Class name
• Data members public, private, (protected)
• Function members
• Service functions (usually public)
• Utility functions (usually private)
• Predicate functions. Example warnings, status
  indicators, error indicators, etc.
• Write a driver that carries out the interaction
  among the objects.

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Member functions

• Member functions are based on use cases
• Ask the question What is an object of this class
  used for? And enumerate its uses.
• This list will indicate to the designed one or
  more functions that need to be implemented to
  fulfill the use case

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Object instantiation

• If you are interested in a specific car Then an
  instance of the class can be created
• Example car mycar, rentedCar
• mycar and rentedCar are objects of class car.
• It is also possible to set a specific
  characteristic such as color, if it is public.
• Example mycar.color green
• If an attribute is private then an access
  function is needed to set its values.

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Basic syntax class definition

• class class_name
• public
• list of class attributes (variables, types,
  constants, and so on) that may be accessed by
  name from outside the class.
• list of prototypes for each member function that
  may be accessed by name from outside the class.
• private
• list of class attributes (variables, types,
  constants, and so on) that are intended to be
  hidden for reference from outside the class.
• list of prototypes for each member function
  intended to be hidden from outside of the class.

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Access specifiers- private and public

• The scope of a specifier begin with the keyword
  private or public and ends when at the end of the
  class or at another access specifier.
• There can be more than one private or public
  sections. But it is a good programming style to
  pool all the public items into a single public
  section and all private into a single private
  section.
• By default all items in a class are private! So
  dont forget to publicize.
• The items in a private section of a class are
  available only to the member function of the
  class.

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Simple definition of class Counter

• class Counter
• public
• Counter() //constructor
• void setCount( int val)
• int getCount()
• void increment ( int n)
• void decrement ( int n)
• private
• int count

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Class constructor(s)

• A class constructor is used to create
  (instantiate) an object of the class.
• The constructor is automatically executed each
  time an object (of class type) is declared.
• A class constructor has the same name as the
  class.
• Ensures all objects start in a consistent state
  and contains the initialization code.
• A constructor cannot specify a return type or
  explicitly return a value.
• A class typically has more than one constructor
  default constructor, copy constructor and
  (converter) or initializing constructor.

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constructor implementation

• operator is called the class resolution
  operator. The class name before defines the
  class context in which a function is defined.
• CounterCounter()// default constructor
• count 0
• CounterCounter(int value)
• // initializing constructor
• count value

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Member Function implementations

• syntax
• type class_namefname (list of formal parameter
  types and names)
• function body

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Object Instantiation and Invoking Member Functions

• Counter score
• score.setCount(45)
• score.increment()
• score.decrement()
• int x score.getCount()

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Files Involved
include Counter.h
Counter.cpp
Counter.h
include Counter.h
Application.cc
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Summary

• Class definition, implementation, usage were
  illustrated
• Three principles of OO design encapsulation,
  inheritance, polymorphism. We looked at examples
  for the first two.
• Problem statement to Object-oriented design.
• Notion of class and object instantiation were
  illustrated.
• Access control specifiers were introduced.