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905-FBAS/ BSSE /F-09 (B)

FACTORY DESIGN PATTERN

a)Factory pattern comes into creational design pattern category, the main objective of the

creational pattern is to instantiate an object and in Factory Pattern an interface is responsiblefor creating the object but the sub classes decides which class to instantiate. It is like the

interface instantiate the appropriate sub-class depending upon the data passed.

Now in the example that we are looking at for explaining the Factory Design Pattern is we

are creating an object of Dog and Cat without calling the Dog or Cat class. We have created

an abstract class Mammals. This class will be used by the Dog and Cat class. We have

created Cat class, this class extends from Mammals class. We have created Dog class, this

class extends from Mammals class. We have to create an object for Dog class and for that we

are not directly loading the Dog class. Instead we are instantiated the object for Mammals

Factory class.

Class Diagram:

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905-FBAS/ BSSE /F-09 (B)

Participants: Mamals Cats Dogs Factory Client Mamals Factory

SINGLETONa) Logging messages is one of the most common tasks performed in software applications. Logging

appropriate messages at appropriate stages can be extremely useful for debugging and monitoring

applications. We define a interface Logger that declares the interface to be used by the client

objects to log messages.

In general, an incoming message could be logged to different output media, in different formats.

Suppose two implementer classes of the Logger are FileLogger and ConsoleLogger .

FileLogger stores incoming messages to a log file. ConsoleLogger displays messages on the screen.

Suppose One of the implementers of the Logger interface , the FileLogger class, logs incoming

messages to the file log.txt.

Singleton is helpful when there is one physical instance of object what the object represents. This is

true in the case of a fileLogger because there is only one physical Log file. In an application, when

different objects try to log messages to the file, there could be a multiple instances of the fileLogger

class in use by each of the client object.

Class Diagram:

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905-FBAS/ BSSE /F-09 (B)

Participants: FileLogger Logger Interface

PROXYa)-A proxy object creates a single object. Clients request are first received by the proxy object but

never processed directly by the Proxy object. Client request are always forwarded to the target object.

Response to the request is guaranteed provide he communication between client and server location is

working.

Class Diagram:

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905-FBAS/ BSSE /F-09 (B)

Participants: Customer Proxy Customer Interface Account Manager