Design Facade

8/12/2019 Design Facade

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Facade Design P

By VI

2

attern

PIN T.M

13H112049G



Structural Patte

● Structural patterns are coand objects are composestructures.Structural clas

compose interfaces or im ● g . aca e, apter, ec

ns

cerned with how classesto form largerpatterns use inheritance to

lementations rator



Structure



Purpose

Provide a unified interfacesubsystem. Facade definethat makes the subsyste

o a set of interfaces in as a higher-level interfaceeasier to use.



Motivation

Reduce Complexity: Introdprovides a single, simplifiegeneral facilities of a subsy

uce a facade object thatinterface to a more

tem.



Applicability

● You want to provide a sisubsystem.A facade can pof the subsystem that is g

clients. Only clients need

● You want to layer your su

ple interface to a complexrovide a simple default viewod enough for most

ing more customizability.

systems.



=



Collabarations

Clients communicate witrequests to Facade, whicappropriate subsystem o

subsystem objects perfor

interface to subsystem in

Clients that use the facasubsystem objects directl

the subsystem by sendingforwards them to the

ject(s). Although the

the actual work, the

erfaces.

e don't have to access its.



Sub classes

class A:def Do_A_Task(self):

print "Executing A"

class B:def Do_B_Task(self):

print "Executing B"

class C:def Do_C_Task(self):

print "Executing C"



class Facade:

def doAllTask(self):

#Creates objects of A,B an

Aobj.Do_A_Task()

Bobj.Do_B_Task(). _ _

if __name__=="__main__":

Facadeobj=Facade()Facadeobj.doAllTask()

C.(Aobj,Bobj,Cobj)



Real Life Exampl es



Compiler

Consistes of componentsanalyzer,parser etc.

In most cases client is lea

individual components.It nter ace comp e w c

such as a lexical

st concerned about these

would like to have aoes a t e tas s



Online Travel B oking Website



public class HotelBooker{public ArrayList<Hotel> getHo

to){//returns hotels available in th}}

public class FlightBooker

public ArrayList<Flight> getFli{//returns flights available in t

}}

elNamesFor(Date from, Date

particular date range

ghtsFor(Date from, Date to)

he particular date range



public class TravelFacade{private HotelBooker hotelBooprivate FlightBooker flightBopublic void getFlightsAndHot{

ArrayList<Flight> flights = fto);

ArrayList<Hotel> hotels = hto);//process and return

}}public class Client

{ public static void main(String[{TravelFacade facade = new T

facade.getFlightsAndHotel

}}

er; ker;

ls(Date from, Data to)

ightBooker.getFlightsFor(from,

telBooker.getHotelsFor(from,

args)

avelFacade();(from, to);



Consequences

Shielding clients from sucoupling b/w subsystem

It shields clients from sut ere y re ucing t e nudeal with and making th

Does not prevent clientsunderlying classes

system promotes weaknd the clients.

system components,er o o jects t at c ients

subsystem easier to use

rom accessing the



References Design Patterns: Elements o

Software,Eric Gama et al, IS

http://javapapers.com/desi

pattern/

http://en.wikipedia.org/wiki

http://www.tutorialspoint.c

pattern.htm

Reusable Object-Oriented

N: 0201633612

n-patterns/facade-design-

/Facade_pattern

m/design_pattern/facade_

Design Facade

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