Transcript OBJECT ORIENTED PROGRAMMING

OBJECT ORIENTED
PROGRAMMING
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!
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.
POINTS OF DISCUSSION
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Object
Message
Event
Class
Property
Inheritance
Data Abstraction and
Encapsulation
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.
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.
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”.
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.
PROPERTY AND EVENTS
• An event is a signal for the object to
perform its function
• Properties are defined characteristics of the
object
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 program’s progress
• Encapsulate data and functions into objects
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.
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.
INHERITANCE
• Promotes reuse
• Programmers don’t 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.
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.
DATA ABSTRACTION
• Loosely defined category
of objects that can be
manipulated and used in a
variety of different
programs.
DATA ENCAPSUALTION
Providing access to an
object only through its
messages, while keeping
the details private
A SIMPLE EXAMPLE
Suppose, you wanted a data type called list(list of
names)
Struct list{
<definition of list structure here>
};
List a, b, c;
a = “Mary Jones”;
b = “Suzy Smith”;
A SIMPLE EXAMPLE
In C, adding the integers a and b
produces an error; the language
doesn’t know what to do with a
and b because they are not
numeric entities. They are
strings –
A SIMPLE EXAMPLE
a:=List fromString: ‘Mary Jones’.
b:=List fromString: ‘Suzy Smith’.
C:=a+b.
Output:
‘Mary Jones, Suzy Smith’
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’
OBJECT ORIENTED LANGUAGES
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There are almost two dozen of them today!
The leading commercial OOL’s 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
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
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.
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 language’s object oriented power!
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.
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++.
Java - OBJECT ORIENTED
LANGUAGE
• Java is designed as a portable language that
can run on any web-enabled computer via
that computer’s 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.
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.
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.
SUMMARY
• An object is a bundle of variables and
related methods
• A method is an operation which can modify
an object’s behavior.
• A Class is a blueprint of an object.
• When defining a Class, you must consider
any possible sub class.
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.
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.
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.