1. Structural PatternStructural Pattern
Dr. Himanshu Hora
SRMS College of Engineering & Technology
Bareilly (UP) INDIA
Dr. Himanshu Hora
SRMS College of Engineering & Technology
Bareilly (UP) INDIA
01/16/16
Structural Pattern
1

2. ContentContent
• History of Design Pattern
• Definitions of Design Pattern
• Types of Pattern
• Adapter
• Bridge
• Composite
• Decorator
• Facade
• Flyweight
• Proxy
• Benefits and Possible problems
• History of Design Pattern
• Definitions of Design Pattern
• Types of Pattern
• Adapter
• Bridge
• Composite
• Decorator
• Facade
• Flyweight
• Proxy
• Benefits and Possible problems
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3. History of Design PatternHistory of Design Pattern
• In 1994, Design Patterns: Elements of Reusable Object-
Oriented Software by Erich Gamma, Richard Helm, Ralph
Johnson and John Vlissides explained the usefulness of
patterns and resulted in the widespread popularity of design
patterns.
• These four authors together are referred to as the Gang of Four
(GoF).
• In 1994, Design Patterns: Elements of Reusable Object-
Oriented Software by Erich Gamma, Richard Helm, Ralph
Johnson and John Vlissides explained the usefulness of
patterns and resulted in the widespread popularity of design
patterns.
• These four authors together are referred to as the Gang of Four
(GoF).
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4. Definitions of Design PatternDefinitions of Design Pattern
• Design patterns are recurring solutions to software design
problems you find again and again in real-world application
development
OR
• Design patterns represent solutions to problems that arise
when developing software within a particular context
OR
• Design patterns are standard solutions to common problems in
software design
• Design patterns are recurring solutions to software design
problems you find again and again in real-world application
development
OR
• Design patterns represent solutions to problems that arise
when developing software within a particular context
OR
• Design patterns are standard solutions to common problems in
software design
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5. Types of PatternTypes of Pattern
There are 3 types of pattern
• Creational: address problems of creating an object in a
flexible way. Separate creation, from operation/use.
• Structural: address problems of using O-O constructs like
inheritance to organize classes and objects
• Behavioral: address problems of assigning responsibilities to
classes. Suggest both static relationships and patterns of
communication (use cases)
There are 3 types of pattern
• Creational: address problems of creating an object in a
flexible way. Separate creation, from operation/use.
• Structural: address problems of using O-O constructs like
inheritance to organize classes and objects
• Behavioral: address problems of assigning responsibilities to
classes. Suggest both static relationships and patterns of
communication (use cases)
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6. Types of PatternTypes of Pattern
Creational Patterns
(concerned with abstracting the object-instantiation process)
• Factory Method Abstract Factory Singleton
• Builder Prototype
Structural Patterns
(concerned with how objects/classes can be combined to form larger
structures)
• Adapter Bridge Composite
• Decorator Facade Flyweight
• Proxy
Behavioral Patterns
(concerned with communication between objects)
• Command Interpreter Iterator
• Mediator Observer State
• Strategy Chain of Responsibility Visitor
• Template Method
Creational Patterns
(concerned with abstracting the object-instantiation process)
• Factory Method Abstract Factory Singleton
• Builder Prototype
Structural Patterns
(concerned with how objects/classes can be combined to form larger
structures)
• Adapter Bridge Composite
• Decorator Facade Flyweight
• Proxy
Behavioral Patterns
(concerned with communication between objects)
• Command Interpreter Iterator
• Mediator Observer State
• Strategy Chain of Responsibility Visitor
• Template Method
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7. AdapterAdapter
• Convert the interface of a class into another interface clients
expect
• Adapter lets classes work together that couldn't otherwise
because of incompatible interfaces
• Use the Adapter pattern when:
– you want to use an existing class and its interface does not
match the one you need
– you need to use several existing subclasses, but it's
impractical to adapt their interface by subclassing
everyone. An object adapter can adapt the interface of its
parent class
• Convert the interface of a class into another interface clients
expect
• Adapter lets classes work together that couldn't otherwise
because of incompatible interfaces
• Use the Adapter pattern when:
– you want to use an existing class and its interface does not
match the one you need
– you need to use several existing subclasses, but it's
impractical to adapt their interface by subclassing
everyone. An object adapter can adapt the interface of its
parent class
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8. AdapterAdapter
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9. BridgeBridge
• Decouple an abstraction from its implementation so that the
two can vary independently
• Use the Bridge pattern when:
– you want run-time binding of the implementation
– you want to share an implementation among multiple
objects
• Decouple an abstraction from its implementation so that the
two can vary independently
• Use the Bridge pattern when:
– you want run-time binding of the implementation
– you want to share an implementation among multiple
objects
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10. BridgeBridge
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11. CompositeComposite
• Compose objects into tree structures to represent whole-part
hierarchies. Composite lets clients treat individual objects and
compositions of objects uniformly
• Use this pattern whenever you have "composites that contain
components, each of which could be a composite".
• Compose objects into tree structures to represent whole-part
hierarchies. Composite lets clients treat individual objects and
compositions of objects uniformly
• Use this pattern whenever you have "composites that contain
components, each of which could be a composite".
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12. CompositeComposite
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13. DecoratorDecorator
• Attach additional responsibilities to an object dynamically
• Decorators provide a flexible alternative to subclassing for
extending functionality
• Attach additional responsibilities to an object dynamically
• Decorators provide a flexible alternative to subclassing for
extending functionality
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14. ProblemsProblems
• Several classes with a similar operation (method), but
different behavior.
• We want to use many combinations of these behaviors
• Several classes with a similar operation (method), but
different behavior.
• We want to use many combinations of these behaviors
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15. Example - Automated HospitalExample - Automated Hospital
• People come to the reception with problems
• They describe their problems
• A special doctoRobot is created that is specialized to treat
their special situations.
• People come to the reception with problems
• They describe their problems
• A special doctoRobot is created that is specialized to treat
their special situations.
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16. Automated Hospital - Solution 1Automated Hospital - Solution 1
DoctoRobot
Cure (p : Patient)
DentistRobot
Cure (p : Patient)
DermaRobot
Cure (p : Patient)
PsychoRobot
Cure (p : Patient)
DentistDermaRobot DentistPsychoRobot DermaPsychoRobot
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17. Problems with solution-1Problems with solution-1
• Sometimes we don’t have multiple inheritance.
• Even if we have, if is problematic, and bad design.
• Sometimes we don’t have multiple inheritance.
• Even if we have, if is problematic, and bad design.
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18. A Better idea: Use DecoratorA Better idea: Use Decorator
ConcreteComponent
Operation( )
ConcreteDecoratorA
addedState
Operation( )
ConcreteDecoratorB
Operation( )
Decorator
Operation( )
Component
Operation( )
component
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19. Decorator in our caseDecorator in our case
DentistRobot
Cure (p : Patient)
DermaRobot
Cure (p : Patient)
PhsychoRobot
Cure (p : Patient)
DoctorRobotDecorator
innerDoctor
Cure (p : Patient)
DoctoRobot
Cure (p : Patient)
component
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20. FacadeFacade
• Provide a unified interface to a set of interfaces in a subsystem
• Facade defines a higher-level interface that makes the
subsystem easier to use
• Create a class that is the interface to the subsystem
• Clients interface with the Facade class to deal with the
subsystem
• It hides the implementation of the subsystem from clients
• It promotes weak coupling between the subsystems and its
clients
• It does not prevent clients from using subsystems class, should
it?
• Provide a unified interface to a set of interfaces in a subsystem
• Facade defines a higher-level interface that makes the
subsystem easier to use
• Create a class that is the interface to the subsystem
• Clients interface with the Facade class to deal with the
subsystem
• It hides the implementation of the subsystem from clients
• It promotes weak coupling between the subsystems and its
clients
• It does not prevent clients from using subsystems class, should
it?
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21. FacadeFacade
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22. FlyweightFlyweight
• Use sharing to support large numbers of fine-grained objects
efficiently
• The pattern can be used when:
– The program uses a large number of objects and
– The program does not use object identity (==)
• Use sharing to support large numbers of fine-grained objects
efficiently
• The pattern can be used when:
– The program uses a large number of objects and
– The program does not use object identity (==)
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23. FlyweightFlyweight
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24. ProxyProxy
• Provide a surrogate or placeholder for another object to
control access to it.
• The proxy has the same interface as the original object
• Virtual Proxy:
– Creates/accesses expensive objects on demand
– You may wish to delay creating an expensive object until it
is really accessed
– It may be too expensive to keep entire state of the object in
memory at one time
• Provide a surrogate or placeholder for another object to
control access to it.
• The proxy has the same interface as the original object
• Virtual Proxy:
– Creates/accesses expensive objects on demand
– You may wish to delay creating an expensive object until it
is really accessed
– It may be too expensive to keep entire state of the object in
memory at one time
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25. • Protection Proxy
– Provides different objects different level of access to
original object
• Cache Proxy (Server Proxy)
– Multiple local clients can share results from expensive
operations: remote accesses or long computations
• Firewall Proxy
– Protect local clients from outside world
• Protection Proxy
– Provides different objects different level of access to
original object
• Cache Proxy (Server Proxy)
– Multiple local clients can share results from expensive
operations: remote accesses or long computations
• Firewall Proxy
– Protect local clients from outside world
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26. ProxyProxy
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27. Benefits
• Flexible
• Don’t have to foresee all combinations
• Little objects
Possible problems
• Performance
• Decorators are not necessarily always cummutative
(surgeon and Anastasiolic)
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28. Thank You
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Dr. Himanshu Hora
SRMS College of Engineering & Technology
Bareilly (UP) INDIA
Dr. Himanshu Hora
SRMS College of Engineering & Technology
Bareilly (UP) INDIA