INTRODUCTION TO OBJECT ORIENTED
PROGRAMMING
Lecture slides by:
Farhan AmjadA new paradigm of programming
LEARNING OUTCOMES After this lecture, you should be able to
Difference of OO technique by other techniques
Understand the meaning of objectKnow the difference between an object and
a classKnow the concepts of object orientationUnderstand how objects communicate
OOPS
It’s OOP not OOPS
COURSE OUTLINE Detailed Course Outline is on the subject homepage
http://groups.google.com/group/sp09_bcs2
Check your email often for announcements related to the course
RESOURCES Recommended Books:
OOP using C++ 6th Edition, Prentice Hall Reference Books:
OOP in C++ by Robert Lafore Thinking in C++, 2nd Edition, by Bruce Eckel
FIVE TIPS TO SUCCESS
WORK HARD
TRY MORE EXERCISES AND MORE PRACTICE
DO THE LABS AND ASSIGNMENTS YOURSELF
BE PATIENT WITH THE MACHINE
IF YOU REALLY NEED THAT, DO IT QUIETLY ...
But not in Class. What you have to do is just inform me about your situation and I will not mark your absent.
Course Policy
THE 5-MINUTE RULE
Applicable rules and submission deadlines will be indicated with the assignments
No make-ups
ASSIGNMENTS
10-15 minutes duration Will cover reading assignments and material covered in the class
Unannounced
No make-ups
QUIZZES
Supervised Lab Sessions and Tutorials will be organized as and when required.
TUTORIALS/LAB SESSIONS
CLASS QUESTIONS I will ask questions very often
So be attentive
PROGRAMMING Actually, programming is not so easy,
because a real good program is not easily programmed. It needs the programmers’ lots of wisdom, lots of knowledge about programming and lots of experience.
It is like writing, to be a good writer needs lots of experience and lots of knowledge about the world.
Learning and practice are necessary.
UNSTRUCTURED PROGRAMMING Usually, people start
learning programming by writing small and simple programs consisting only of one main program. Here ``main program'' stands for a sequence of commands or statements which modify data which is global throughout the whole program.
Main Program
Data
DRAWBACKS This programming technique can only be
used in a very small program. For example, if the same statement
sequence is needed at different locations within the program, the sequence must be copied. If an error needed to be modified, every copy needs to be modified.
This has lead to the idea to extract these sequences(procedure), name them and offering a technique to call and return from these procedures.
PROCEDURAL PROGRAMMING
With procedural programming, you are able to combine sequences of calling statements into one single place.
A procedure call is used to invoke the procedure. After the sequence is processed, flow of control proceeds right after the position where the call was made .
Main Program Procedure
PROCEDURES Programs can now be written more
structured and error free. For example, if a procedure is correct,
every time it is used it produces correct results.
Consequently, in cases of errors you can narrow your search to those places which are not proven to be correct.
COMPILATION PROCESS & TRANSLATOR TYPES
PROCEDURE PROGRAM VIEW
Now a program can be viewed as a sequence of procedure calls.
The main program is responsible to pass data to the individual calls, the data is processed by the procedures and the resulting data is presented.
Thus, the flow of data can be illustrated as a hierarchical graph, a tree.
PROCEDURE PROGRAM VIEW
Main Program
Data
Procedure1
Procedure2
Procedure3
MODULAR PROGRAMMING
Modular programming is subdividing your program into separate subprograms such as functions and subroutines.
With modular programming, procedures of a common functionality are grouped together into separate modules.
A program therefore no longer consists of only one single part. It is now divided into several smaller parts which interact through procedure calls and which form the whole program.
Main Program(Also a module)
Data
Data Data1
Module2
+Data Data2
Module1
+Data Data1
Procedure1Procedure2
The main program coordinates calls to procedures in separate modules and hands over appropriate data as parameters.
Procedure3
MODULAR PROGRAMMING
Each module can have its own data. This allows each module to manage an internal state which is modified by calls to procedures of this module.
Each module has its own special functionalities that supports the implementation of the whole program.
STRUCTURAL PROGRAMMING
Also structured programming A subset of procedural programming
that enforces a logical structure on the program being written to make it more efficient and easier to understand and modify.
Certain languages such as Ada, Pascal, and dBASE are designed with features that encourage or enforce a logical program
PROBLEMS WITH STRUCTURED APPROACH
Function
Global DataGlobal Data Global Data
Function Function Function
PROBLEMS WITH STRUCTURED APPROACH When the program grows larger and more
complex even the structural programming shows the strain.
You may have heard horror stories of project’s complexity, schedule slipping etc.
In procedural programming data is given second class status.
Inventory system-> new programmer->writes the function
It is same like you are sitting in your lobby and left there your personal documents.
OBJECT-ORIENTATION
It is a kind of thinking methodologyEverything in the world is an object;Any system is composed of objects (certainly a
system is also an object);The evolution and development of a system is
caused by the interactions among the objects inside or outside the system
WHAT IS OBJECT ORIENTED PROGRAMMING?
Build programming using software objects.
Means that we organize software as a collection of discrete (different) objects that incorporate both data structure and behavior.
In OOP, the software objects correspond closely to real objects involve in the application area.
EVERYTHING IN THE WORLD IS AN OBJECT
A flower, a tree, an animal A student, a professor A desk, a chair, a classroom, a building A university, a city, a country The world, the universe A subject such as CS, IS, Math, History,
…
ANY SYSTEM IS COMPOSED OF OBJECTS
A law system A cultural system An educational system An economic system An Information system A computer system
THE DEVELOPMENT OF A SYSTEM IS CAUSED BY THE INTERACTIONS
University is developed by the interactions among:studentsprofessorsstaffsofficers of Bio-scienceofficers of CIIT… ...
OBJECT-ORIENTED PROGRAMMING & ADT
ADTs allows the creation of instances with well-defined properties and behavior.
In object-orientation, ADTs are referred to as classes. Therefore, a class defines properties of objects which are
the instances in an object-oriented environment. Object-oriented programming is ``programming with
ADTs'': combining functionality of different ADTs to solve a problem.
Therefore instances (objects) of ADTs (classes) are dynamically created, destroyed and used.
Object1
Data1+Procedures1
Data Data1 Object3
Data3 + Procedures3
Object2
Data2 + Procedures2
Object4
Data4 + Procedures4
OBJECT-ORIENTED LANGUAGES
An object-based programming language is one which easily supports object-orientation.
Smalltalk:1972-1980, Alan Kay C++:1986, Bjarne Stroustrup Java:1992 (Smalltalk + C++), James
Gosling C#:
Developed at Microsoft by Anders Hejlsberg et al, 2000 Event driven, object oriented, visual programming
language (C++ and Java)
WHY OOP? ◆ Complexity & Haste:
Skilled programmer: 10-15 lines of code a day
Price ~ $18/line Can you pay this? If not, what will you
do?Hire non professionals?
◆ OOP fights Complexity:A more realistic model of the worldCollection of interacting objects instead of a
collection of functionsReuse of ready made components
REUSABILITY: Reduce development cost:
one component instead of many Promote reliability:
exercise component from many different aspects
no need to remember to correct the same error twice
REUSE, REUSE…………… INFO TECH RESEARCH FUNDING
The Clinton Administration has targeted 5technology areas for support from the NationalInstitute of Standards & Technology, and twofocus directly on information technology: anationwide health care information infrastructureand an effort to develop reusable softwarecomponents for large software systems.[Wall Street Journal, 26 April ‘94, Page B6]Reuse is tightly coupled with abstraction:
● Identify similarity between elements.● Create a component that represents the similar parts.● Rewrite elements to use the common part.
EXTENDIBILITY & MODIFIABILITY Adding new features responding to
changing operation environment can be a matter of introducing a few new objects.
Easy to make minor changes in the data representation/ the procedures used in an OO program. Changes within an object do not affect any other parts of the program.
FLEXIBILITY, MAINTAINABILITY & REUSEABILITY Flexibility
Very flexible in accommodating different situations because the interaction patterns among the object can be changed without modifying the object.
MaintainabilityObjects can be maintained separately.Reusability
Objects can be reused in the different programs.
DATA IS IMPORTANT Data is more important then functions,
methods, procedures etc but in procedural languages data is given the second class status. OOP also provides the mechanism to hide the data.
Example: Importance of data in inventory system,
banking system etc.You hire a new programmer and he
accidently changes the corrupts the data. Same like someone changes your personal data.
REASON’S FOR HIDING Reduces complexity much like the
detailed workings of an automobile are hidden from the average driver.
Principle of least privilege (need-to-know)
More Secure. Less likely that someone will alter or misuse something.
Easier to change the implementation without affecting other modules that use it.
DIFFERENT TERMINOLOGIES
Classes Objects Data encapsulation Inheritance Polymorphism
CHARACTERISTICS OF OO
Class A generic definition for a set of
similar objects. Provides the specifications for the
objects’ behaviors and attributes. An abstraction of a real world entity.
CHARACTERISTICS OF OO
The key concepts are: Object
Directly relate to the real world entities.
Can be a person, thing or concept.Like a “black box”, therefore all the implementation is hidden.
Has a State (attribute) Behavior (operation) Identity (unique name)
CHARACTERISTICS OF OO Object vs Class object is created from a class. object is considered as an instance of a
class. class is considered as a template from
which objects are instantiated can create an object or many objects
from a class.
CHARACTERISTICS OF OO
Diagram 1: Class Car
Car
DoorSeatTypeModel
DriveStopLockUnlock
Diagram 2: MyCar as an ObjectObject vs Class
CHARACTERISTICS OF OO
Messages Requests for the receiver objects to
carry out the indicated method or behavior and return the result of that action to the sender objects
CHARACTERISTICS OF OO
Encapsulation Process of hiding the
implementation details of an object. Access to manipulate the object
data is through its interface (operations/ functions).
Protects an object’s internal state from being corrupted by other programs.
CHARACTERISTICS OF OO
Encapsulation (cont) Program maintenance is easier and
less expensive because changes in the object data or implementation is only modified in one place
Allows objects to be viewed as black boxes.
CHARACTERISTICS OF OO
Inheritance Code reuse mechanism to build
new objects out of old ones. Defines a relationship among
classes where one class shares the structure and/or behavior on one or more classes.
Provides a more flexible and adaptable system and enables polymorphism.
CHARACTERISTICS OF OO
Polymorphism Means having many forms. Provides the ability to use a single
message to invoke many different kinds of behavior.
Same name with different meaning.
PROTECTION Protected levels in a class:
Public: Can be accessed both within and external to the object.
Private: Can only be used by the object itself.
The public section of a class is usually called the interface. It is what the programmers sees.
Normally, All data is private and only the bare essential functions are made public.
SUMMARY What is Object Oriented
Programming? Object-oriented programming is a
method of implementation in which programs are organized as cooperative collections of objects, each of which represents an instance of some class, and whose classes are all members of one or more hierarchy of classes united via inheritance relationships
REFERENCES: OOP by Robert Lafore OOP by Deitel and Deitel Haibin Zhu, Ph. D. Associate Professor of
CS, Nipissing University Complete Reference