object oriented programming (oop) - cs304 power point slides lecture 06

8/13/2019 Object Oriented Programming (OOP) - CS304 Power Point Slides Lecture 06

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Object-Oriented Programming(OOP)

Lecture No. 6


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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


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Class Compatibility

Derived class is usually a subtype of thebase class

It can handle all the legal messages(operations) of the base class

Therefore, base class can always bereplaced by the derived class


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ExampleClass Compatibility

Shapecolor

vertices

move

setColordraw

Circleradiusdraw

computeArea

Linelength

draw

getLength

Triangle

angle

draw

computeArea


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ExampleClass Compatibility

Filesize

open

print

ASCII Fileprint

PDF File

print

PS File

print


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Polymorphism

In general, polymorphism refers toexistence of different forms of a singleentity

For example, both Diamond and Coal aredifferent forms of Carbon


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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 does

not need to know exact class of the receiver


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ExamplePolymorphism

Shape

Line Circle Triangle

draw

draw

draw draw

drawView


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ExamplePolymorphism

File

ASCII File PDF File PS File

print

print

print print

printEditor


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PolymorphismAdvantages

Messages can be interpreted in differentways depending upon the receiver class

Shape

Line Circle Triangledraw

draw

draw draw

drawView


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New classes can be added without changingthe existing model

Squaredraw

Shape

Line Circle Triangledraw

draw

draw draw

drawView


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In general, polymorphism is a powerful toolto develop flexible and reusable systems


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Object-Oriented Modeling

An Example


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Problem Statement

Develop a graphic editor that can drawdifferent geometric shapes such as line,circle and triangle. User can select, move or

rotate a shape. To do so, editor providesuser with a menu listing differentcommands. Individual shapes can be

grouped together and can behave as asingle shape.


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Identify Classes

Extract nouns in the problem statement

Develop a graphic editorthat can drawdifferent geometric shapessuch as line,circleand triangle. Usercan select, move orrotate a shape. To do so, editorprovides

userwith a menulisting differentcommands. Individual shapescan begrouped together and can behave as asingle shape.


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Identify Classes

Eliminate irrelevant classes

EditorVery broad scope

UserOut of system boundary


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Identify Classes

Add classes by analyzing requirements

Grouprequired to behave as a shapeIndividual shapes can be grouped together and

can behave as a single shape

Vieweditor must have a display area


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Identify Classes

Shape

Line

Circle

TriangleMenu

Group

View

Following classes have been identified:


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Object ModelGraphic Editor

Line

Circle

Triangle

GroupShape

View

Menu


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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)


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Verify access paths

View contains shapesView contains lines

View contains circles

View contains triangles

View contains groups

(Aggregation)


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Verify access paths

Menu sends message to View(Simple One-Way Association)


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TriangleCircleLine

ShapeView

nnnnnn

nn

Menu

Group

nn

nnnn

nn

nn


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Identify Attributes

Extract properties of the object

From the problem statement

Properties are not mentioned


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Identify Attributes

Extract properties of the object From the domain knowledge

Line

Color

Vertices

Length

Circle Color

Vertices

Radius

Triangle

Color

Vertices

Angle

Shape Color

Vertices


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Identify Attributes

Extract properties of the object From the domain knowledge

Group

noOfObjects

View

noOfObjects

selected

Menu

Name

isOpen


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Menu

nameisOpen

View

noOfObjectsselected

Shape

colorvertices

Linelength

Circleradius GroupnoOfObjectsTriangleangle

nn

n

nn

n

nn

n

n

nn

nn

nn

n


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Identify Operations

Extract verbs connected with an object

Developa graphic editor that can draw

different geometric shapes such as line,circle and triangle. User can select, move

or rotatea shape. To do so, editor provides

user with a menu listing different

commands. Individual shapes can be

groupedtogether and can behaveas a

single shape.


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Identify Operations

Eliminate irrelevant operations

Develop out of system boundary

Behavehave broad semantics


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Identify Operations

Following are selected operations:

Line

Draw

Select

Move

Rotate

Circle

Draw

Select

Move

Rotate


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Identify Operations


Triangle

Draw

Select

Move

Rotate

Shape

Draw

Select

Move

Rotate


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Identify Operations


Group

Draw Select

Move

Rotate

Menu

Open Select

Move

Rotate


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Identify Operations

Extract operations using domainknowledge

ViewAdd

Remove

Group

Show

Select

Move

Rotate


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Group

noOfObjects

draw()

Triangle

angle

draw()nnCircle

radius

draw()nn

Line

length

draw()

nn

Shape

colorvertices

draw()select()move()

rotate()nn

View

noOfObjectsselected

add()remove()group()show()select()move()rotate()

nn

nnnn

nn

Menu

nameisOpen

open()select()move()

rotate()

n


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Identify Inheritance

Search is a kind of by looking at keywordslike such as, for example, etc

shapes such as line, circle and triangle Line, Circle and Triangle inherits from Shape


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Identify Inheritance

By analyzing requirements

Individual shapes can be grouped togetherand can behave as a single shape

Group inherits from Shape


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Refining the Object Model

Application of inheritance demands aniteration over the whole object model

In the inheritance hierarchy,

All attributes are shared

All associations are shared

Some operations are shared

Others are overridden


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Share associations

View contains all kind of shapes

Group consists of all kind of shapes


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Share attributes

ShapeLine, Circle, Triangle and Group

Color, vertices


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Share operations


Select

Move Rotate


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Share the interface and overrideimplementation


Draw


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Line

length

draw()

Circle

radius

draw()

Triangle

angle

draw()

Group

noOfObjects

draw()

Shape

colorvertices


rotate()

n

View

noOfObjects

selected

add()remove()group()show()

select()move()rotate()

nn

Menu

nameisOpen


rotate()

n


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Group

noOfObjects

draw()

Triangle

angle

draw()nnCircle

radius

draw()nn

Line

length

draw()

nn

Shape

colorvertices


rotate()nn

View

noOfObjectsselected

add()remove()group()show()select()move()rotate()

nn

nnnn

nn

Menu

nameisOpen


rotate()

n

object oriented programming (oop) - cs304 power point slides lecture 06

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