Template Method Pattern

Template Method Pattern

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  Template Method PatternHigh Level Algorithm Monis Iqbal Snr. Software Engineer Creative Chaos (pvt.) Limited
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  Definition Define theskeleton of an algorithm in an operation, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure. <GOF>
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  Different implementations ofalgorithms leading to different algorithm altogether. (Similar code maintained differently) Every class requires full knowledge of the algorithm. Code duplication (Yuc!!)
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  Algorithm encapsulated insingle class Single control/entry point. Subclasses only need to provide specialized algorithm details.
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  Primitive Methods Abstractclass declares primitive methods leaving the subclasses to provide functionality. Primitive methods used in Template Method . Nicely documented and meaningfully named.
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  Concrete methods Usedin Template method Defined in abstract class Declared final
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  Hooks Hook placedin the Template method. Abstract class provides implementation. Subclasses can “hook into” the algorithm if they want.
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  abstract class AbstractClass{ final void templateMethod() { primitiveOperation1(); primitiveOperation2(); concreteOperation(); if (hookIsTrue()) hook(); } abstract void primitiveOperation1(); abstract void primitiveOperation2(); void final concreteOperation() { … .. } boolean hookIsTrue() { return false; } void hook() {} }
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  Cache revisited Exampleby Code First in First Out (FIFO) Cache Least Recently Used (LRU) Cache
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  Intuition Encapsulation ofAlgorithm Don’t call us, we’ll call you. (Hollywood Principle).
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  Questions ???