Template method pattern: Difference between revisions

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In [[software engineering]], the '''template method pattern''' is a [[behavioral pattern|behavioral]] [[software design pattern|design pattern]] that defines the [[program skeleton]] of an [[algorithm]] in an operation, deferring some steps to [[Subclass (computer science)|subclass]]es.<ref name=":0">{{cite book

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| publisher = Addison-Wesley

| isbn = 0-201-63361-2

}}</ref> It lets one redefine certain steps of an algorithm without changing the algorithm's structure.<ref name=":2">{{cite book|url=http://shop.oreilly.com/product/9780596007126.do|title=Head First Design Patterns|last2=Freeman|first2=Elisabeth|last3=Sierra|first3=Kathy|last4=Bates|first4=Bert|publisher=O'REILLY|year=2004|isbn=978-0-596-00712-6|editor-last=Hendrickson|editor-first=Mike|volume=1|___location=|pagepages=289, 311|pages=|format=paperback|quote=|editor-last2=Loukides|editor-first2=Mike|via=|last1=Freeman|first1=Eric|accessdate=2012-09-12}}</ref>

==Overview==

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Usually, subclasses control how the behavior of a parent class is redefined, and they aren't restricted to redefine only certain parts of a behavior.

<big>What solution does the Template Method design pattern describe?</big>

Define abstract operations (''primitives'') for the variant parts of a behavior.

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==Introduction==

In the template method of this design pattern, one or more algorithm steps can be overridden by subclasses to allow differing behaviors while ensuring that the overarching algorithm is still followed.<ref name=":0" />

In object-oriented programming, a concrete class is created that provides the steps of an [[algorithm design]]. Steps that are considered invariant are implemented inside the base class. The steps that are considered to be variant, are given a default implementation or none at all. These variant steps must be supplied by concrete derived subclasses.<ref name=":1" /> Thus the general algorithm is saved in one place but the concrete steps may be changed by the subclasses.

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== Structure ==

=== UML class diagram ===

[[File:w3sDesign Template Method Design Pattern UML.jpg|frame|none|A sample UML class diagram for the Template Method design pattern. <ref>{{cite web|title=The Template Method design pattern - Structure |url=http://w3sdesign.com/?gr=b10&ugr=struct|website=w3sDesign.com|accessdate=2017-08-12}}</ref>]]

In the above [[Unified Modeling Language|UML]] [[Class diagram|class diagram]], the <code>AbstractClass</code> defines a <code>templateMethod()</code> operation that

defines the skeleton (template) of a behavior by

* implementing the invariant parts of the behavior and

* calling abstract <code>primitive1()</code> and <code>primitive2()</code> operations to defer implementing the variant parts to <code>SubClass1</code>.<br>

=== Class diagram ===

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* [http://www.24bytes.com/2011/10/template-method.html Template Method Example]

{{Design Patterns Patterns}}

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