Structural patterns

Structural patterns (Design Pattern)

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 Pattern Types 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 Pattern Types 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. Adapter Adapter
•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. Adapter Adapter
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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. Composite 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".
•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. Composite Composite
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13. Decorator Decorator
•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. Facade Facade
•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. Facade Facade
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22. Flyweight Flyweight
•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. Flyweight Flyweight
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24. Proxy Proxy
•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. Proxy Proxy
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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