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Abstract Factory Design Pattern

Abstract Factory Design Pattern. making abstract things. Abstract vs. Concrete. a number of design patterns use abstract and concrete classes abstract class – provides a list of abstract functions to be used by the pattern concrete class – provides implementation for the abstract functions

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Abstract Factory Design Pattern

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  1. Abstract FactoryDesign Pattern making abstract things

  2. Abstract vs. Concrete • a number of design patterns use abstract and concrete classes • abstract class – provides a list of abstract functions to be used by the pattern • concrete class – provides implementation for the abstract functions • abstract class pointers may point to concrete class objects and the abstract functions are overridden by concrete implementations • clients may not be concerned with implementations • various concrete objects may be assembled into a single container and operated uniformly • virtual functions would provide customized functionality per object

  3. Factory and Factory Methods • factory – an object for creating other objects called products • important when control over object creation is necessary: e.g. instead of just creating an object, factory may dynamically allocate it from an object pool, do complex configurations • contains methods for object creation • factory method (design pattern)- implements the actual object creation • usually returns a pointer to created object • specifies interface to be implemented (overridden) by subclasses, hence known as virtual constructor • why not regular constructor? cannot be overridden • example of behavior pattern • singleton class is an example of a factory, why?

  4. Abstract Factory • regular factory encodes product class names. May be inconvenient • in case need to make modification • in case need to re-use code for several related factories • abstract factorydesign pattern – separates interface and implementation • abstract factory – specifies creation interface • abstract product – specifies product interface to be manipulated by abstract factory • abstract factory method - product creation interface • concrete factory, product, method – implementation of respective interfaces • benefit of abstract factory pattern – client may not need to know (concrete) implementations to operate objects • abstract factory pattern is a creational pattern • abstract factory is often designed as a singleton pattern • a factory may be part abstract/part concrete

  5. Abstract Factory UML Diagram

  6. Review Questions • what is the difference between abstract and concrete classes? How can a client benefit from this difference? • what is: factory? product? factory method? • why are the factory and product separated into abstract and concrete?

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