Abstraction http://ecomputernotes.com

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” http://ecomputernotes.com

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 http://ecomputernotes.com

Example – Abstraction Ali is a PhD student and teaches BS students behaviour - Study - DevelopExam - GiveExam - TakeExam - PlaySports - Eat - DeliverLecture - Walk http://ecomputernotes.com

Example – Abstraction Attributes - Name - Employee ID - Student Roll No - Designation - Year of Study - Salary - CGPA - Age Student’s Perspective http://ecomputernotes.com

Example – Abstraction Student’s Perspective behaviour - Study - DevelopExam - GiveExam - TakeExam - PlaySports - Eat - DeliverLecture - Walk http://ecomputernotes.com

Example – Abstraction Attributes - Name - Employee ID - Student Roll No - Designation - Year of Study - Salary - CGPA - Age Teacher’s Perspective http://ecomputernotes.com

Example – Abstraction Teacher’s Perspective behaviour - Study - DevelopExam - GiveExam - TakeExam - PlaySports - Eat - DeliverLecture - Walk http://ecomputernotes.com

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 http://ecomputernotes.com

Example – Abstraction Driver’s View Engineer’s View http://ecomputernotes.com

Abstraction – Advantages Simplifies the model by hiding irrelevant details Abstraction provides the freedom to defer implementation decisions by avoiding commitment to details http://ecomputernotes.com

Classes In an OO model, some of the objects exhibit identical characteristics (information structure and behaviour) We say that they belong to the same class http://ecomputernotes.com

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 http://ecomputernotes.com

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 http://ecomputernotes.com

Graphical Representation of Classes (Class Name) (attributes) (operations) (Class Name) Normal Form Suppressed Form http://ecomputernotes.com

Example – Graphical Representation of Classes Circle center radius draw computeArea Normal Form Suppressed Form Circle http://ecomputernotes.com

Example – Graphical Representation of Classes Person name age gender eat walk Normal Form Suppressed Form Person http://ecomputernotes.com

Inheritance A child inherits characteristics of its parents Besides inherited characteristics, a child may have its own unique characteristics http://ecomputernotes.com

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 http://ecomputernotes.com

Example – Inheritance Person Teacher Doctor Student http://ecomputernotes.com

Example – Inheritance Shape Circle Triangle Line http://ecomputernotes.com

Inheritance – “IS A” or “IS A KIND OF” Relationship Each derived class is a special kind of its base class http://ecomputernotes.com

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

Example – “IS A” Relationship Shape color coord draw rotate setColor Circle radius draw computeArea Line length draw Triangle angle draw computeArea

Inheritance – Advantages Reuse Less redundancy Increased maintainability http://ecomputernotes.com

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 http://ecomputernotes.com

Example Reuse Shape color coord draw rotate setColor Circle radius draw computeArea Line length draw Triangle angle draw computeArea

Example Reuse Person name age gender eat walk Teacher designation salary teach takeExam Student program studyYear study heldExam Doctor designation salary checkUp prescribe

Example Reuse Person name age gender eat walk Teacher designation salary teach takeExam Student program studyYear study heldExam Doctor designation salary checkUp prescribe