Object-Oriented Programming
(OOP)
Lecture No. 6
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Class Compatibility-Object Oriented Programming-Lecture Slides, Slides of Object Oriented Programming
Main topics in this course are object-orientation, objects and classes, overloading, inheritance, polymorphism, generic programming, exception handling, introduction to design patterns. This lecture includes: Class, Compatability, Subtype, Operation, Behaviour, Polymorphism, Model, Advantage, Reciever, Draw
Typology: Slides
2011/2012
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Object-Oriented Programming
(OOP)
Lecture No. 6
Class Compatibility
►
A class is behaviorally compatible withanother if it supports all the operations ofthe other class
►
Such a class is called subtype
►
A class can be replaced by its subtype
Example – Class Compatibility
Shape
colorverticesmovesetColordraw
Circle
radiusdrawcomputeArea
Line
lengthdraw
Triangle
angledrawcomputeArea
Example – Class Compatibility
File
size…openprint…
ASCII File
… print…
PDF File
PS File
… print…
Polymorphism in OO Model
►
In OO model, polymorphism means thatdifferent objects can behave in differentways for the same message (stimulus)
►
Consequently, sender of a message doesnot need to know exact class of the receiver
Example – Polymorphism
Shape
Line
Circle
Triangle
draw
draw draw
draw
draw
View
Polymorphism – Advantages
►
Messages can be interpreted in differentways depending upon the receiver class
Shape
Line
Circle
Triangle
draw
draw draw
draw
draw
View
Polymorphism – Advantages
►
New classes can be added without changingthe existing model
Square
draw
Shape
Line
Circle
Triangle
draw
draw draw
draw
draw
View
Object-Oriented Modeling
An Example
Problem Statement
►
Develop a graphic editor that can drawdifferent geometric shapes such as line,circle and triangle. User can select, move orrotate a shape. To do so, editor providesuser with a menu listing differentcommands. Individual shapes can begrouped together and can behave as asingle shape.
…Identify Classes
Eliminate irrelevant classes
►
Editor – Very broad scope
►
User – Out of system boundary
…Identify Classes
Add classes by analyzing requirements
►
Group – required to behave as a shape
“Individual shapes can be grouped together andcan behave as a single shape”
►
View – editor must have a display area
Object Model – Graphic Editor
Line
Circle
Triangle
Group
Shape
View
Menu
Identify Associations
Extract verbs connecting objects
“Individual shapes can be groupedtogether”
Group consists of lines, circles, triangles
Group can also consists of other groups
(Composition)