OBJECT ORIENTED PROGRAMMING

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OBJECT ORIENTED PROGRAMMING
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What is Object Oriented Software?

• Software based on the creation of objects
• An object is a black box which receives and
  sends messages
• A black box contains code and data, which are
  merged into a single indivisible object
• As a user - Do not peek into the box!

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Why is it so famous?

• Offers a new and powerful model for writing
  computer software
• Improves maintenance, reusability and
  modifiability
• Improves principles of modularity and information
  hiding.

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POINTS OF DISCUSSION

• Object
• Message
• Event
• Class
• Property
• Inheritance
• Data Abstraction and Encapsulation

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INTRODUCTION

• Object Oriented Programming models real-world
  objects with software counterparts, H.M.Deitel
  P.J.Deitel
• It is a type of programming where a programmer
  defines both data types and functions of a data
  structure.

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What is an Object?

• OOP encapsulates data and functions into packages
  called objects, that are intimately tied
  together.
• Objects are individual instances of a class.

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So, what is a class?

• It determines everything about an object.
• Spot is an object created from class Dog.
• A method is simply the action that a message
  carries out.
• The Dog class defines messages that the Dog
  objects can understand, like bark and fetch.

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Message

• Messages define the interface to the object
• All communication to the object is done via the
  messages
• Objects do not ordinarily perform their behavior
  spontaneously, rather a specific behavior is
  invoked when a message is sent.

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PROPERTY AND EVENTS

• An event is a signal for the object to perform
  its function
• Properties are defined characteristics of the
  object

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PROPERTIES

• Take advantage of class relationships, where
  objects of a certain class have the same
  characteristics
• Provide a more natural and intuitive way of
  viewing the programs progress
• Encapsulate data and functions into objects

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INHERITANCE

• Inheritance is a form of software reusability
  in which new classes are created from existing
  classes by the absorption of attributes and
  behaviors, embellishing these with capabilities
  the new class requires.

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INHERITANCE

• In any good Object Oriented language, the
  programmer creates a subclass of the original
  class. This new class inherits all the existing
  messages, and therefore, all the behavior of the
  original class.
• The original class is called the parent class or
  Super class, of the new class.
• A subclass is said to be a specialization of its
  super class, and conversely, a super class a
  generalization of its subclass.

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INHERITANCE

• Promotes reuse
• Programmers dont start from the scratch when
  they write a new program. They reuse an existing
  repertoire of classes that have behaviors similar
  to what is required in the new program.
• For example, after creating the class Dog, you
  might create a subclass called Wolf, which
  defines some wolf specific messages such as hunt.

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INHERITANCE

• It is more sensible to define a common class
  called Canine, of which both Dog and Wolf are sub
  classes
• Much of the art of OOP is determining the best
  way to divide a program into an economical set of
  classes.
• In addition to speeding development time, proper
  class construction and reuse results in far fewer
  lines of code, which translates to less bugs, and
  lower maintenance costs.

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DATA ABSTRACTION

• Loosely defined category of objects that can be
  manipulated and used in a variety of different
  programs.

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DATA ENCAPSUALTION

• Providing access to an object only through its
  messages, while keeping the details private

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A SIMPLE EXAMPLE

• Suppose, you wanted a data type called list(list
  of names)
• Struct list
• ltdefinition of list structure heregt
• List a, b, c
• a Mary Jones
• b Suzy Smith

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A SIMPLE EXAMPLE

• In C, adding the integers a and b produces an
  error the language doesnt know what to do with
  a and b because they are not numeric entities.
  They are strings

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A SIMPLE EXAMPLE

• aList fromString Mary Jones.
• bList fromString Suzy Smith.
• Cab.
• Output
• Mary Jones, Suzy Smith

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A SIMPLE EXAMPLE

• The first two lines of code simply create List
  objects a and b from the two strings. This now
  works, because the list class was created with a
  method which specifically knows how to handle
  the message . Hence, C will have the new value
  of a combination of the argument with its own
  object by striking them together with a comma
  separating them.
• Mary Jones, Suzy Smith

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OBJECT ORIENTED LANGUAGES

• There are almost two dozen of them today!
• The leading commercial OOLs are
• C
• Smalltalk
• Java
• C is an OO version of C
• Smalltalk is significantly faster to develop than
  C
• Java is the latest, flashiest OO language

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C - OBJECT ORIENTED LANGUAGE

• C is compatible with C (superset of C), so
  that existing code can be incorporated into C
  programs. C programs are fast and efficient,
  qualities which helped make C an extremely
  popular programming language. It sacrifices
  certain flexibility in order to remain efficient

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C - OBJECT ORIENTED LANGUAGE

• C uses compile-time binding, which means the
  programmer must specify the specific class of an
  object, which makes for high run-time efficiency
  and small code size, but it trades off some of
  the power to reuse the classes.
• C has become so popular that most new compilers
  are C/C compilers.

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C - OBJECT ORIENTED LANGUAGE

• However, in order to take full advantage of OOP,
  one must program in C, not C.
• This often can be a major problem for C
  programmers.
• Many programmers think they are coding in C,
  but instead are only using a small part of the
  languages object oriented power!

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Smalltalk - OBJECT ORIENTED LANGUAGE

• C makes some practical compromises to ensure
  fast execution and small code size, Smalltalk
  makes none.
• It uses run-time binding, which means that
  nothing about the type of an object need be known
  before a Smalltalk program is run.
• Smalltalk has a rich class library that can be
  easily reused via inheritance.

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Smalltalk - OBJECT ORIENTED LANGUAGE

• It also has a dynamic development environment
• Smalltalk is not explicitly compiled, like C
• It is syntactically very simple, much more so
  than either C or C.

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Java - OBJECT ORIENTED LANGUAGE

• Java is designed as a portable language that can
  run on any web-enabled computer via that
  computers web browser. As such, it offers great
  promise as the standard internet and intranet
  programming language.
• Java is a mixture of C and Smalltalk!
• It has no pointers, low-level programming
  constructs that make error-prone programs.

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Java - OBJECT ORIENTED LANGUAGE

• Like Smalltalk, Java has garbage collection, a
  feature that frees the programmer from explicitly
  allocating and de-allocating memory.
• It runs on a Smalltalk-style virtual machine,
  software built into web browser which executes
  the same standard compiled Java byte codes
  irrespective of the computer used.

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Powerbuilder - OBJECT ORIENTED LANGUAGE

• PowerBuilder is an object oriented application
  tool that allows to build powerful, multitier
  applications to run on multiple platforms and to
  interact with various databases.
• Each menu or window you create is an object.
• Each object contains properties, events and
  functions.

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SUMMARY

• An object is a bundle of variables and related
  methods
• A method is an operation which can modify an
  objects behavior.
• A Class is a blueprint of an object.
• When defining a Class, you must consider any
  possible sub class.

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CONCLUSION

• Major advantages of OOP are
• It can address the problems that increasing size
  and complexity cause
• Produce more complete and understandable
  specifications and designs by using all major
  types of data abstraction
• This approach speeds up the development of new
  programs, improves maintenance and reusability.

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CONCLUSION

• However, OOP requires a major shift in thinking
  by programmers.
• The C offers an easier transition via C, but
  it still requires an OO design approach.
• Java promises much for web-enabling OO programs.
• Smalltalk offers a pure OO environment.

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BIBLIOGRAPHY

• C How to Program - Deitel Deitel
• Object Oriented Analysis - David Brown
• Object Oriented Analysis and Design with
  applications - Grady Booch
• What is Object-Oriented Software? An article by
  Terry Montlick
• Design, Implementation and Management - Peter Rob
  Carlos Coronel.