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Structural patterns
- 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 01/16/16 Structural Pattern 2
- 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). 01/16/16 Structural Pattern 3
- 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 01/16/16 Structural Pattern 4
- 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) 01/16/16 Structural Pattern 5
- 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 01/16/16 Structural Pattern 6
- 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 01/16/16 Structural Pattern 7
- 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 01/16/16 Structural Pattern 9
- 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". 01/16/16 Structural Pattern 11
- 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 01/16/16 Structural Pattern 13
- 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 01/16/16 Structural Pattern 14
- 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. 01/16/16 Structural Pattern 15
- 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 01/16/16 Structural Pattern 16
- 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. 01/16/16 Structural Pattern 17
- 18. A Better idea: Use DecoratorA Better idea: Use Decorator ConcreteComponent Operation( ) ConcreteDecoratorA addedState Operation( ) ConcreteDecoratorB Operation( ) Decorator Operation( ) Component Operation( ) component 01/16/16 Structural Pattern 18
- 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 01/16/16 Structural Pattern 19
- 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? 01/16/16 Structural Pattern 20
- 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 (==) 01/16/16 Structural Pattern 22
- 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 01/16/16 Structural Pattern 24
- 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 01/16/16 Structural Pattern 25
- 27. Benefits • Flexible • Don’t have to foresee all combinations • Little objects Possible problems • Performance • Decorators are not necessarily always cummutative (surgeon and Anastasiolic) 01/16/16 Structural Pattern 27
- 28. Thank You 01/16/16 Structural Pattern 28 Dr. Himanshu Hora SRMS College of Engineering & Technology Bareilly (UP) INDIA Dr. Himanshu Hora SRMS College of Engineering & Technology Bareilly (UP) INDIA