structural pattern

8/16/2019 Structural Pattern

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STRUCTURAL

PATTERNB A Y U P R I Y A M B A D H A


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STRUCTURAL PATTERN

• Decorator Pattern

• Adapter Pattern

• Façade Pattern

• Composite Pattern

•

Proxy Pattern


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DE C O R A T O R

PATTERN


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DECORATOR PATTERN

• This type of design pattern comes under structural pattern.

• Attach additional responsibilities to an object dynamically. Decorators provide a

alternative to subclassing for extending functionality.

• This pattern creates a decorator class which wraps the original class and provid

functionality keeping class methods signature intact.

• Wrapping a gift, putting it in a box, and wrapping the box.

• so known as:

– Wrapper


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APLICABILITY

• To add responsibilities to individual objects dynamically and transparently, that is

affecting other objects.

• For responsibilities that can be withdrawn

• When extension by subclassing is impractical

– sometimes a large number of independent extensions are possible and would produ

of subclasses to support every combination

– a class definition may be hidden or otherwise unavailable for subclassing


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DECORATOR PATTERN


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A D A P T E R

PATTERN


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ADAPTER PATTERN

• Adapter pattern works as a bridge between two incompatible interfaces.

• This pattern involves a single class which is responsible to join functionalities of

or incompatible interfaces.

• Adapter lets classes work together that couldn't otherwise because of incompat


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ADAPTER PATTERN : MOTIVATION


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ADAPTER PATTERN : MOTIVATION

• Sometimes a toolkit or class library can not be used because its interface is incothe interface required by an application

• We can not change the library interface, since we may not have its source code

• Even if we did have the source code, we probably should not change the library domain-specific application


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ADAPTER PATTER : STRUCTURE


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F A Ç A D E

PATTERN


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FAÇADE PATTERN

• Provide a unified interface to a set of interfaces in a subsystem

• Façade defines a higher-level interface that makes the subsystem easier to use

• Façade pattern hides the complexities of the system and provides an interface t

using which the client can access the system.

• This pattern involves a single class which provides simplified methods required b

delegates calls to methods of existing system classes.


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FAÇADE PATTERN : MOTIVATION


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FAÇADE PATTERN : STRUCTURE


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FAÇADE PATTERN : EXAMPLE


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C O M P O S I T E

PATTERN


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COMPOSITE PATTERN

• Compose objects into tree structures to represent part-whole hierarchies

• Composite lets clients treat individual objects and compositions of objects unifo

• This pattern creates a class that contains group of its own objects. This class pro

modify its group of same objects.


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COMPOSITE PATTERN : STRUCTU


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PRO XY PATT E


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PROXY PATTERN

• Provide a surrogate or placeholder for another object to control access to it.

• Use an extra level of indirection to support distributed, controlled, or intelligent

• Add a wrapper and delegation to protect the real component from undue comp

• Problem :

– You need to support resource-hungry objects, and you do not want to instantiate s

unless and until they are actually requested by the client.


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PROXY PATTERN : STRUCTURE


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structural pattern

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