UNIT-III dp

7/21/2019 UNIT-III dp

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UNIT-III

Creational Patterns


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S.NO. TOPIC

1 Creational Pattern Part-I Introduction

4 Factory Method

5 Prototype6 Singleton

7 Repeated key points or Structural Patterns !Intent"Moti#ation" $lso %no&n $s '''''(

8 !discussion o Creational patterns( Re#ie& )nit-III

* $+stract Factory

, uilder

PP. Slides

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/* 2 0 *

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Creational Patterns

$+stracts instantiation process

Makes syste independent o ho& its o+ects

are created

coposed

represented

ncapsulates kno&ledge a+out &hich concrete

classes the syste uses ides ho& instances o these classes are

created and put together

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Creational Patterns

$+stract the instantiation process Make a syste independent o ho& o+ects are created" coposed"

and represented

Iportant i systes e#ol#e to depend ore on o+ect

coposition than on class inheritance

phasis shits ro hardcoding i8ed sets o +eha#iors to&ards asaller set o coposa+le undaental +eha#iors

ncapsulate kno&ledge a+out concrete classes a syste

uses

ide ho& instances o classes are created and put together

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Benefts o creationalpatterns Creational patterns let you program to

an interace defned by an abstractclass

That lets you confgure a system withproduct objects that vary widely instructure and unctionality

Example !"# systems #nter$iews !"# class library %ultiple loo&'and'eels (bstract )actories or di*erent screen

components

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Benefts o creationalpatterns !eneric instantiation + ,bjects are instantiated

without having to identiy a specifc class typein client code -(bstract )actory. )actory/

0implicity + %a&e instantiation easier callersdo not have to write long complex code toinstantiate and set up an object -Builder.1rototype pattern/

Creation constraints + Creational patterns canput bounds on whocan create objects. howthey are created. and whenthey are created

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ABSTRACT FACTORY

(Object Creational) Intent9

Pro#ide an interace or creating ailies o

related or dependent o+ects &ithout speciyingtheir concrete classes

Also Known As: %it:

/*


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Motivation

; Moti#ation9;)ser interace toolkit supports ultiple

look-and-eel standards

!Moti" Presentation Manager(

;


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Widget Factory

CreateScrollar!(

Create=indo&!(

MotifWidgetFactory

CreateScrollar!(

Create=indo&!(

PMWidgetFactory

CreateScrollar!(

Create=indo&!(

Client

Windows

PMWindow MotifWindow

ScrollBar

PMScrollBar MotifScrollBar

ABSTRACT FACTORY

Motivation

/*


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; Solution9;$+stract =idget Factory class

;Interaces or creating each +asic kind

o &idget;$+stract class or each kind o

&idgets"

;Concrete classes ipleent speciic

look-and-eel:

/*


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Alicabilit!

)se the $+stract Factory pattern &hen

$ syste should +e independent :

$ syste should +e conigured &ith one o ultiple

ailies o products:

$ aily o related product o+ects is designed to +e

used together:

>ou &ant to pro#ide a class li+rary o products:

/*


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?perations9

CreateProd$! (

CreateProc! (

$+stractFactory

?perations9

CreateProd$! (

CreateProc! (

ConcreteFactory1

?perations9

CreateProd$! (

CreateProc! (

ConcreteFactory*

$+stractProduct$

ConcreteProduct$1 ConcreteProduct$*

$+stractProduct

ConcreteProduct1 ConcreteProduct*

client

Abstract Factor! Str"ct"re/*


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ABSTRACT FACTORY Particiants $+tractFactory!=idget Factory(


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Collaborations ?nly one ConcreteFactory instance is used or an

acti#ation" atched to a speciic application conte8t: It

+uilds a speciic product aily or client use -- the client

doesn@t care &hich aily is used -- it siply needs the

ser#ices appropriate or the current conte8t:

.he client ay use the $+stractFactory interace to

initiate creation" or soe other agent ay use the

$+stractFactory on the client@s +ehal:

/*


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Conse#"ences .he $+stract Factory Pattern has the ollo&ing +eneits9

It isolates concrete classes ro the client: >ou use the $+stract Factory to control the classes o

o+ects the client creates:

8changing product ailies is easy: Aone o the client code +reaks +ecause the a+stract

interaces don@t change:

ecause the a+stract actory creates a coplete aily o

products" the &hole product aily changes &hen the

concrete actory is changed: It prootes consistency aong products:

It is the concrete actory@s o+ to ake sure that the right

products are used together:

/*


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I$le$entation Factories as singletons:

$pplication needs only one instance o aConcreteFactory:

Creating the products $+stract Factory only declares an interace or creating

products:


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%no& Uses Inter#ie&s

used to generate Blook and eel or speciic user

interace o+ects

uses the %it sui8 to denote $+stractFactory classes"

e:g:" =idget%it and


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Relate' Patterns

Factory Method -- a B#irtual constructor

Prototype -- asks products to clone

thesel#es

Singleton -- allo&s creation o only a single

instance

/*


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BUI*R

PATT*RN Intent9Separate the construction o a cople8 o+ect ro

its representation so that the sae constructionprocess can create dierent representations

Moti#ation9 R.F reader should +e a+le to con#ert R.F to

any te8t orat $dding ne& con#ersions &ithout odiying thereader should +e easy

/,


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; Solution9

;Conigure R.FReader class &ith a .e8tCon#erter o+ect

;Su+classes o .e8t Con#erter specialiGe

in dierent con#ersions and orats;.e8t=idgetCon#erter &ill produce a

cople8 )I o+ect and lets the user see

and edit the te8t

/,


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RTFReader

ParseR.F!(

&hile!tHget the ne8t token(

s&itch t:.ype

C$R9

+uilder-JCon#ertCharacter!t:Char(

F?A.9

+uilder-JCon#entFontCharnge!t:Font(

P$R$9

uilder-JCon#entParagraph!(

K

K

TextConverter

Con#ertCharacter!char(

Con#ertFontChange!Font(

Con#ertParagraph!(

ASCConverter


Let$SCII.e8t!(

TextConverter



Con#ertParagraph!(

Let.eE.e8t!(

TextWidgestConverter



Con#ertParagraph!(

Let.e8t=idget!(

$SCII.e8t .eE.e8t.e8t=idget

+uilders

BUI*R Motivation

/,


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Alicabilit!

)se the uilder pattern &hen .he algorith or creating a cople8 o+ect should

+e independent o the parts that ake up the

o+ect and ho& they are asse+led .he construction process ust allo& dierent

representations or the o+ect that is constructed

/,


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!irector

Construct !(

or all o+ects in structure

+uilder-JuildPart !(

K

B"ilder

uildPart !(

ConcreteB"ilder

uildPart !(

LetResult !(

Prod"ct

+uilders

BUI*R

Str"ct"re

/,


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Particiants uilder!.e8tCon#erter(

Speciies an a+stract interace or creating parts o

a Product o+ect:

Concreteuilder!$SCIICon#erter".eECon#erter".e8t

=idgetCon#erter( Constructs and asse+les parts o the product:


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B"il'er - Collaborations

Client creates


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a


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Conse#"ences

It lets #ary a product@s internal representation:

It isolates code or construction and

representation:

It gi#es iner control o#er the construction

process:


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I$le$entation

Assembly and construction interface uilders construct their products in step-+y-step

ashion:

No abstract classes for interface Empty methods as default in Builder.

In cDD" the +uild ethods are not declared as pure

#irtual e+er unctions:


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%no&n Uses

R.F application is ro .DD:

uilder is a coon pattern in Salltalk-3:


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Relate' Patterns

$+stract actory is siilar to uilder: It too

constructs cople8 o+ects:

Coposite is oten &hat the uilder +uilds:

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