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Contents • • • • • • • • • • • • • • • • Overview [ ] The Factory Method design pattern is one of the twenty-three well-known that describe how to solve recurring design problems to design flexible and reusable object-oriented software, that is, objects that are easier to implement, change, test, and reuse. The Factory Method design pattern solves problems like: • How can an object be created so that subclasses can redefine which class to instantiate? • How can a class defer instantiation to subclasses?

Creating an object directly within the class that requires (uses) the object is inflexible because it commits the class to a particular object and makes it impossible to change the instantiation independently from (without having to change) the class. The Factory Method design pattern describes how to solve such problems: • Define a separate operation ( factory method) for creating an object. • Create an object by calling a factory method. This enables writing of subclasses to change the way an object is created (to redefine which class to instantiate). See also the UML class diagram below.

Definition [ ] 'Define an interface for creating an object, but let subclasses decide which class to instantiate. The Factory method lets a class defer instantiation it uses to subclasses.' () Creating an object often requires complex processes not appropriate to include within a composing object. The object's creation may lead to a significant duplication of code, may require information not accessible to the composing object, may not provide a sufficient level of abstraction, or may otherwise not be part of the composing object's.

The factory method design pattern handles these problems by defining a separate for creating the objects, which can then override to specify the of product that will be created. The factory method pattern relies on inheritance, as object creation is delegated to subclasses that implement the factory method to create objects. Structure [ ] UML class diagram [ ].

A sample UML class diagram for the Factory Method design pattern. In the above, the Creator class that requires a Product object doesn't instantiate the Product1 class directly.

Instead, the Creator refers to a separate factoryMethod() to create a product object, which makes the Creator independent of which concrete class is instantiated. Subclasses of Creator can redefine which class to instantiate. In this example, the Creator1 subclass implements the abstract factoryMethod() by instantiating the Product1 class.

Example [ ] Structure [ ]. Room is the base class for a final product ( MagicRoom or OrdinaryRoom). MazeGame declares the abstract factory method to produce such a base product. Diljale Movie Hd Video Song Download. MagicRoom or OrdinaryRoom are subclasses of the base product implementing the final product. MagicMazeGame and OrdinaryMazeGame are subclasses of MazeGame implementing the factory method producing the final products.

Thus factory methods decouple callers ( MazeGame) from the implementation of the concrete classes. This makes the 'new' Operator redundant, allows adherence to the and makes the final product more flexible in the event of change. Example implementations [ ] Java [ ] A maze game may be played in two modes, one with regular rooms that are only connected with adjacent rooms, and one with magic rooms that allow players to be transported at random (this example is similar to one in the book ). The MazeGame uses Rooms but it puts the responsibility of creating Rooms to its subclasses which create the concrete classes. The regular game mode could use this template method. 'Empty vocabulary of actual object Public Interface IPerson Function GetName () As String End Interface Public Class Villager Implements IPerson Public Function GetName () As String Implements IPerson. GetName Return 'Village Person' End Function End Class Public Class CityPerson Implements IPerson Public Function GetName () As String Implements IPerson.

GetName Return 'City Person' End Function End Class Public Enum PersonType Rural Urban End Enum '' '' Implementation of Factory - Used to create objects '' Public Class Factory Public Function GetPerson ( type As PersonType ) As IPerson Select Case type Case PersonType. Rural Return New Villager () Case PersonType. Urban Return New CityPerson () Case Else Throw New NotSupportedException () End Select End Function End Class C# [ ] Same code for C#. From abc import ABCMeta, abstractmethod from enum import Enum class Person ( metaclass = ABCMeta ): @abstractmethod def get_name ( self ): raise NotImplementedError ( 'You should implement this!' ) class Villager ( Person ): def get_name ( self ): return 'Village Person' class CityPerson ( Person ): def get_name ( self ): return 'City Person' class PersonType ( Enum ): RURAL = 1 URBAN = 2 class Factory: def get_person ( self, person_type ): if person_type == PersonType. RURAL: return Villager () elif person_type == PersonType. URBAN: return CityPerson () else: raise NotImplementedError ( 'Unknown person type.'

) factory = Factory () person = factory. Get_person ( PersonType. URBAN ) print ( person. Get_name ()) Uses [ ] • In, is an example of the use of factory method to connect parallel class hierarchies.

• In, is a factory method declared in a framework that can be overridden in. • In, several factories are used in the package. Javax.xml.parsers.DocumentBuilderFactory or javax.xml.parsers.SAXParserFactory. See also [ ] •, the highly influential book •, overview of design patterns in general •, a pattern often implemented using factory methods •, another creational pattern •, which may call factory methods • 's idea of a, which he says has no direct equivalent in. References [ ]. • Erich Gamma, Richard Helm, Ralph Johnson, John Vlissides (1994). Design Patterns: Elements of Reusable Object-Oriented Software.

El Poder Del Pensamiento Positivo Pdf Norman Vincent Peale Quotes. Addison Wesley. CS1 maint: Multiple names: authors list () •. Retrieved 2017-08-17. • Freeman, Eric; Freeman, Elisabeth; Kathy, Sierra; Bert, Bates (2004). Hendrickson, Mike; Loukides, Mike, eds.

O'REILLY: 162.. Retrieved 2012-09-12. Retrieved 2017-08-12. •;;;; (June 1999).: Improving the Design of Existing Code. •;; Johnson, Ralph; Vlissides, John (1994).. CS1 maint: Multiple names: authors list () • Cox, Brad J.; (1986).. CS1 maint: Multiple names: authors list () • Cohen, Tal; Gil, Joseph (2007).

Journal of Object Technology.. Retrieved 2007-03-12. External links [ ] The Wikibook has a page on the topic of: • (a Design Description Language) • by Joshua Bloch.