Transcript
Object-Oriented Object-Oriented Programming (OOP)Programming (OOP)
Lecture No. 3Lecture No. 3
AbstractionAbstraction
►Abstraction is a way to cope with Abstraction is a way to cope with complexity.complexity.
►Principle of abstraction:Principle of abstraction:
““Capture only those details about an object Capture only those details about an object that are relevant to current perspective”that are relevant to current perspective”
Example – AbstractionExample – Abstraction
►AttributesAttributes- Name- Name - Employee - Employee
IDID
- Student Roll No- Student Roll No - Designation- Designation
- Year of Study- Year of Study - Salary- Salary
- CGPA- CGPA - Age- Age
Ali is a PhD student and teaches BS students
Example – AbstractionExample – Abstraction
Ali is a PhD student and teaches BS students
►behaviourbehaviour- Study- Study - DevelopExam- DevelopExam
- GiveExam- GiveExam - TakeExam- TakeExam
- PlaySports- PlaySports - Eat- Eat
- DeliverLecture- DeliverLecture - Walk- Walk
Example – AbstractionExample – Abstraction
►AttributesAttributes- Name- Name - Employee - Employee
IDID
- Student Roll No- Student Roll No - Designation- Designation
- Year of Study- Year of Study - Salary- Salary
- CGPA- CGPA - Age- Age
Student’s Perspective
Example – AbstractionExample – Abstraction
Student’s Perspective
►behaviourbehaviour- Study- Study - DevelopExam- DevelopExam
- GiveExam- GiveExam - TakeExam- TakeExam
- PlaySports- PlaySports - Eat- Eat
- DeliverLecture- DeliverLecture - Walk- Walk
Example – AbstractionExample – Abstraction
►AttributesAttributes- Name- Name - Employee - Employee
IDID
- Student Roll No- Student Roll No - Designation- Designation
- Year of Study- Year of Study - Salary- Salary
- CGPA- CGPA - Age- Age
Teacher’s Perspective
Example – AbstractionExample – Abstraction
Teacher’s Perspective
►behaviourbehaviour- Study- Study - DevelopExam- DevelopExam
- GiveExam- GiveExam - TakeExam- TakeExam
- PlaySports- PlaySports - Eat- Eat
- DeliverLecture- DeliverLecture - Walk- Walk
Example – AbstractionExample – Abstraction
►Ordinary PerspectiveOrdinary PerspectiveA pet animal withA pet animal with Four LegsFour Legs A TailA Tail Two EarsTwo Ears Sharp TeethSharp Teeth
►Surgeon’s PerspectiveSurgeon’s PerspectiveA being withA being with A SkeletonA Skeleton HeartHeart KidneyKidney StomachStomach
A cat can be viewed with different perspectives
Example – AbstractionExample – Abstraction
Driver’s View
Engineer’s View
Abstraction – AdvantagesAbstraction – Advantages
►Simplifies the model by hiding Simplifies the model by hiding irrelevant detailsirrelevant details
►Abstraction provides the freedom to Abstraction provides the freedom to defer implementation decisions by defer implementation decisions by avoiding commitment to detailsavoiding commitment to details
ClassesClasses
► In an OO model, some of the objects In an OO model, some of the objects exhibit identical characteristics exhibit identical characteristics (information structure and behaviour)(information structure and behaviour)
►We say that they belong to the same We say that they belong to the same classclass
Example – ClassExample – Class
►Ali studies mathematicsAli studies mathematics►Anam studies physicsAnam studies physics►Sohail studies chemistrySohail studies chemistry
►Each one is a StudentEach one is a Student►We say these objects are We say these objects are instancesinstances of of
the Student classthe Student class
Example – ClassExample – Class
►Ahsan teaches mathematicsAhsan teaches mathematics►Aamir teaches computer scienceAamir teaches computer science►Atif teaches physicsAtif teaches physics
►Each one is a teacherEach one is a teacher►We say these objects are We say these objects are instancesinstances of of
the Teacher classthe Teacher class
Graphical Representation of Graphical Representation of ClassesClasses
(Class Name)
(attributes)
(operations)
(Class Name)
Normal Form
Suppressed Form
Example – Graphical Example – Graphical Representation of ClassesRepresentation of Classes
Circlecenterradius
drawcomputeArea
Normal Form
Suppressed Form
Circle
Example – Graphical Example – Graphical Representation of ClassesRepresentation of Classes
Personnameagegendereatwalk
Normal Form
Suppressed Form
Person
InheritanceInheritance
►A child inherits characteristics of its A child inherits characteristics of its parentsparents
►Besides inherited characteristics, a Besides inherited characteristics, a child may have its own unique child may have its own unique characteristicscharacteristics
Inheritance in ClassesInheritance in Classes
► If a class B inherits from class A then it If a class B inherits from class A then it contains all the characteristics contains all the characteristics (information structure and behaviour) of (information structure and behaviour) of class Aclass A
►The parent class is called The parent class is called basebase class and class and the child class is called the child class is called derivedderived class class
►Besides inherited characteristics, Besides inherited characteristics, derived class may have its own unique derived class may have its own unique characteristicscharacteristics
Example – InheritanceExample – Inheritance
Person
TeacherDoctorStudent
Example – InheritanceExample – Inheritance
Shape
CircleTriangleLine
Inheritance – “IS A” orInheritance – “IS A” or“IS A KIND OF” Relationship“IS A KIND OF” Relationship
►Each derived class is a special kind of Each derived class is a special kind of its base classits base class
Example – “IS A” RelationshipExample – “IS A” RelationshipPerson
nameagegendereatwalk
TeacherdesignationsalaryteachtakeExam
StudentprogramstudyYearstudyheldExam
DoctordesignationsalarycheckUpprescribe
Example – “IS A” RelationshipExample – “IS A” Relationship
ShapecolorcoorddrawrotatesetColor
CircleradiusdrawcomputeArea
Linelengthdraw
Triangleangle
drawcomputeArea
Inheritance – AdvantagesInheritance – Advantages
►ReuseReuse
►Less redundancyLess redundancy
► Increased maintainabilityIncreased maintainability
Reuse with InheritanceReuse with Inheritance
►Main purpose of inheritance is reuseMain purpose of inheritance is reuse►We can easily add new classes by We can easily add new classes by
inheriting from existing classesinheriting from existing classes Select an existing class closer to the Select an existing class closer to the
desired functionalitydesired functionality Create a new class and inherit it from the Create a new class and inherit it from the
selected classselected class Add to and/or modify the inherited Add to and/or modify the inherited
functionalityfunctionality
Example ReuseExample ReuseShape
colorcoorddrawrotatesetColor
CircleradiusdrawcomputeArea
Linelengthdraw
Triangleangle
drawcomputeArea
Example ReuseExample ReusePerson
nameagegendereatwalk
TeacherdesignationsalaryteachtakeExam
StudentprogramstudyYearstudyheldExam
DoctordesignationsalarycheckUpprescribe
Example ReuseExample ReusePerson
nameagegendereatwalk
TeacherdesignationsalaryteachtakeExam
StudentprogramstudyYearstudyheldExam
DoctordesignationsalarycheckUpprescribe
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