Composition over inheritance: Difference between revisions

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[[File:UML diagram of composition over inheritance.svg|thumb|right|444px|This diagram shows how the fly and sound behavior of an animal can be ddesigned in a flexible way by using the composition over inheritance design principle.<ref name="FHDPs" />]]

signed in a flexible way by using the composition over inheritance design principle.<ref name="FHDPs" />]]

'''Composition over inheritance''' (or '''composite reuse principle''') in [[object-oriented programming]] (OOP) is the principle that classes should achieve [[Polymorphism (computer science)|polymorphic]] behavior and [[code reuse]] by their [[object composition|composition]] (by containing instances of other classes that implement the desired functionality) rather than [[Inheritance (computer science)|inheritance]] from a base or parent class.<ref>{{cite book

| url = https://books.google.com/books?id=4pjbgVHzomsC&q=composite+reuse+principle&pg=PA17

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An implementation of composition over inheritance typically begins with the creation of various [[Interface (computing)#In object-oriented languages|interfaces]] representing the behaviors that the system must exhibit. Interfaces can facilitate [[Polymorphism (computer science)|polymorphic]] behavior. Classes implementing the identified interfaces are built and added to [[business ___domain]] classes as needed. Thus, system behaviors are realized without inheritance.

In fact, business ___domain classes may all be base classes without any inheritance at all. Alternative implementation of system behaviors is accomplished by providing another class that implements the desired behavior interface. A class that contains a reference to an interface can support implementations of the interface—a choice that can be delayed until [[Runtime (program lifecycle phase)|runtime]].

accomplished by providing another class that implements the desired behavior interface. A class that contains a reference to an interface can support implementations of the interface—a choice that can be delayed until [[Runtime (program lifecycle phase)|runtime]].

==Example==