2. Study Assignment
• I hope you did go through chapter 1 of both the books.
• How was the experience?
• What did you learn?
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3. Procedural vs. Object-Oriented
• Procedural
Withdraw, deposit, transfer
• Object Oriented
Customer, money, account
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5. What is Object-Orientation?
• A technique for system modeling
• OO model consists of several interacting objects
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6. What is a Model?
• A model is an abstraction of something
• Purpose is to understand the product before developing it
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7. Examples – Model
• Highway maps
• Architectural models
• Mechanical models
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8. Example – OO Model
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9. …Example – OO Model
• Objects
• Ali
• House
• Car
• Tree
• Interactions
• Ali lives in the house
• Ali drives the car
Ali
Car
House
Tree
lives-in
drives
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10. Object-Orientation -
Advantages
• People think in terms of objects
• OO models map to reality
• Therefore, OO models are
• easy to develop
• easy to understand
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11. What is an Object?
An object is
• Something tangible (Ali, Car)
• Something that can be apprehended intellectually (Time,
Date)
***Apprehended intellectually means taken mentally or
logically***
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12. … What is an Object?
An object has
• State (attributes)
• Well-defined behaviour (operations)
• Unique identity
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13. Example – Ali is a Tangible Object
• State (attributes)
• Name
• Age
• behavior (operations)
• Walks
• Eats
• Identity
• His name
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14. Example – Car is a Tangible Object
• State (attributes)
- Color
- Model
• behavior (operations)
- Start Car
- Accelerate
- Change Gear
• Identity
- Its registration number
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15. Example – Time is an Object
Apprehended Intellectually
• State (attributes)
- Hours - Seconds
- Minutes
• behaviour (operations)
- Set Hours - Set Seconds
- Set Minutes
• Identity
- Would have a unique ID in the model
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16. Example – Date is an Object
Apprehended Intellectually
• State (attributes)
- Year - Day
- Month
• behaviour (operations)
- Set Year - Set Day
- Set Month
• Identity
- Would have a unique ID in the model
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17. Definition
• What Is an Object?
• An object is a software bundle of related
variables and methods (functions). Software
objects are often used to model real-world
objects you find in everyday life.
• Objects are key to understanding object-oriented
technology. You can look around you now and
see many examples of real-world objects: dog,
desk, television set, bicycle.
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18. Real-world objects share two
characteristics
• They all have state and behavior
• dogs have state (name, color, breed, hungry) and behavior
(barking, fetching, and wagging tail).
• Bicycles have state (current gear, current pedal cadence, two
wheels, number of gears) and behavior (braking, accelerating,
slowing down, changing gears).
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19. Software objects are modeled after real-
world objects
• A software object maintains its state in one or more variables .
• A software object implements its behavior with methods . A
method is a function (subroutine) associated with an object.
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20. Can represent real-world objects by
using software objects.
• You might want to represent real-world dogs as
software objects in an animation program or a
real-world bicycle as a software object in the
program that controls an electronic exercise
bike.
• You can also use software objects to model
abstract concepts. For example, an event is a
common object used in GUI window systems to
represent the action of a user pressing a mouse
button or a key on the keyboard.
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21. Moving to new thinking …
• C is a procedural language. A procedure is a list of instructions.
• Very small programs (tens of lines) need no organization.
• As they get large (hundreds of lines), they are divided into functions.
• Functions are still lists of instructions.
• Dividing a program into functions gives a structure to the program
(hence structured programming).
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22. Moving to new thinking …
• C programming cannot do the following well:
• Functions have unrestricted access to global data.
• Data and Functions are unrelated; they do not form a logical group or
show any form of binding.
• Cannot model ‘real world’.
• In real world, we deal with objects like cars, people etc.
• Are such objects like ‘data’? Which data type describes a car, for
example?
• Are such objects like ‘functions’? What will a function car() do?
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23. Moving to new thinking …
• A real world object, e.g. car:
• Is its description purely the ability to have a ‘data type’ to represent its
specifications or ‘attributes’ only? For example what attributes describe
a car?
• So by having all these attributes ‘only’ do you know all about a car?
Would you buy a car by merely looking at these attributes and their
values?
• No! What else do you wish to have?
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24. Moving to new thinking …
• A real world object, e.g. car:
• Test drive! Right?
• What would you know through a test drive: how it ‘behaves’ in
response to various stimulus!
• How can it negotiate a speed brake, a speedy turn, full braking etc.
• Effectively, you wish to know how it ‘functions’.
• Behavior is like a function.
• So neither data nor functions, by themselves, model real-world
objects effectively.
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25. Object Oriented Approach …
• Neither data nor functions, by themselves, model real-world
objects effectively.
• OO languages (like C++) combine both ‘data’ and ‘functions that
operate on that data’ into a single unit, called ‘object’. Hence
‘encapsulating’ an entity.
• The objects functions are called member functions.
• Typically, data can be accessed through functions only. So data gets
‘hidden’.
• Data hiding ensures the data is not accidentally altered.
• Reference analogy of a growing company; 2 people vs 100
employee company.
• Objects communicate with each other by calling each other’s
member functions.
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26. Object Oriented Approach …
• OOP is all about ‘organization’ and not about program operation.
Most individual statements are similar to C statements. Member
functions may be very similar to C procedural functions.
• In C you used to think about functions.
• In C++ you should think about objects.
• Often objects in C++ are real-world analogies.(parallel)
• In C++ objects are ‘instances’ of ‘classes’. E.g. Honda City is an
instance of class car!
• Class serves as a cookie cutter and an object a cookie.
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27. Abstraction
• Abstraction is a way to cope with complexity.
• Principle of abstraction:
“Capture only those details about an object that are relevant to
current perspective”
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28. Example – Abstraction
• Attributes
- Name - Employee ID
- Student Roll No - Designation
- Year of Study - Salary
- CGPA - Age
Ali is a PhD student and teaches BS
students
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29. Example – Abstraction
Ali is a PhD student and teaches BS
students
• Behavior
- Study - Develop Exam
- Give Exam - Take Exam
- Play Sports - Eat
- Deliver Lecture - Walk
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30. Example – Abstraction
Attributes
• - Name - Employee ID
• - Student Roll No - Designation
• - Year of Study - Salary
• - CGPA - Age
Student’s Perspective
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31. Example – Abstraction
Student’s Perspective
• behavior
- Study - Develop Exam
- Give Exam - Take Exam
- Play Sports - Eat
- Deliver Lecture - Walk
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32. Example – Abstraction
• Attributes
- Name - Employee ID
- Student Roll No - Designation
- Year of Study - Salary
- CGPA - Age
Teacher’s Perspective
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33. Example – Abstraction
Teacher’s Perspective
• behaviour
- Study - Develop Exam
- Give Exam - Take Exam
- Play Sports - Eat
- Deliver Lecture - Walk
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34. Example – Abstraction
• Ordinary Perspective
A pet animal with
• Four Legs
• A Tail
• Two Ears
• Sharp Teeth
• Surgeon’s Perspective
A being with
• A Skeleton
• Heart
• Kidney
• Stomach
A cat can be viewed with different
perspectives
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36. Abstraction – Advantages
• Simplifies the model by hiding irrelevant details
• Abstraction provides the freedom to defer implementation
decisions by avoiding commitment to details
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37. Classes
• In an OO model, some of the objects exhibit identical
characteristics (information structure and behavior)
• We say that they belong to the same class
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38. Example – Class
• Ali studies mathematics
• Anam studies physics
• Sohail studies chemistry
• Each one is a Student
• We say these objects are instances of the Student class
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39. Example – Class
• Ahsan teaches mathematics
• Aamir teaches computer science
• Atif teaches physics
• Each one is a teacher
• We say these objects are instances of the Teacher class
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40. Graphical Representation of Classes
(Class Name)
(attributes)
(operations)
(Class Name)
Normal Form
Suppressed
Form
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41. Example – Graphical Representation
of Classes
Circle
center
radius
draw
computeArea
Normal Form
Suppressed
Form
Circle
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42. Example – Graphical Representation
of Classes
Person
name
age
gender
eat
walk
Normal Form
Suppressed
Form
Person
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43. Inheritance
• A child inherits characteristics of its parents
• Besides inherited characteristics, a child may have its own
unique characteristics
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44. Inheritance in Classes
• If a class B inherits from class A then it contains all the
characteristics (information structure and behaviour) of class
A
• The parent class is called base class and the child class is called
derived class
• Besides inherited characteristics, derived class may have its
own unique characteristics
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47. Inheritance – “IS A” or
“IS A KIND OF” Relationship
• Each derived class is a special kind of its base class
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48. Example – “IS A” Relationship
Person
name
age
gender
eat
walk
Teacher
designation
salary
teach
takeExam
Student
program
studyYear
study
heldExam
Doctor
designation
salary
checkUp
prescribe
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49. Example – “IS A KIND”
Relationship
Shape
color
cord
draw
rotate
setColor
Circle
radius
draw
computeArea
Line
length
draw
Triangle
angle
draw
computeArea
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50. Inheritance – Advantages
• Reuse
• Less redundancy
• Increased maintainability
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51. Reuse with Inheritance
• Main purpose of inheritance is reuse
• We can easily add new classes by inheriting from existing
classes
• Select an existing class closer to the desired functionality
• Create a new class and inherit it from the selected class
• Add to and/or modify the inherited functionality
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55. References
• “Object Oriented Programming in C++”, by “Robert Lafore”,
published by Sams Publishing (The Waite Group). 4th ed. available
in soft form.
• “Object Oriented Programming Using C++” by “Joyce Farrell” ,
published by Course Technology, Cengage Learning. 4th ed. available
in soft form
• National University of Computer & Emerging Sciences
[www.nu.edu.pk]
• Virtual University of Pakistan [ocw.vu.edu.pk]
• Open Courseware Consortium
[http://www.ocwconsortium.org/en/courses]
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