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Design Pattern

Design Pattern. Dr. Zhen Jiang West Chester University E-mail: zjiang@wcupa.edu url: www.cs.wcupa.edu/~zjiang. Outline. Introduction Creational Patterns Structural Patterns Behavioral Patterns. Introduction.

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Design Pattern

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  1. Design Pattern Dr. Zhen Jiang West Chester University E-mail: zjiang@wcupa.edu url: www.cs.wcupa.edu/~zjiang

  2. Outline • Introduction • Creational Patterns • Structural Patterns • Behavioral Patterns

  3. Introduction • A design pattern names, abstracts, and identifies the key aspects of a common design structure that make it useful for creating a reusable object-oriented design • Creational design patterns abstracts the instantiation process • Structural patterns are concerned with how classes and objects are composed to form larger structures. • Behavioral patterns are concerned with algorithms and assignment of responsibilities between objects.

  4. Creational Pattern • Abstract factory • Builder • Factory Method • Prototype • Singleton

  5. Abstract Factory • Consider a user interface (client, windows and ScrollBar) that supports (creates) multiple look-and-feel standards. Client WidgetFactory Windows PMW Motif Motif PMW ScrollBar ? PMW Motif

  6. Abstract Factory Client AbstractFactory ProductA PA2 PA1 Factory1 Factory2 ProductB PB2 PB1

  7. Abstract Factory • Shopping, interlibrary, …

  8. Builder • Add a new conversion? Converter Reader/User ACS Widget Text Picture

  9. Builder Builder Reader/User ConcreteBuilder Product

  10. Builder • Add a new tool, new course, new equipment, …

  11. Factor Method • For creating objects • Drink, Drug, vegetables, gardening, … Product Creator ConcreteProduct ConcreteCreator

  12. Prototype • Provide an abstract tool for defining items like those in the palette. • Windows creation Prototype Client clone movement Prototype1 Prototype2 clone clone

  13. Singleton • For some classes to have exactly one instance • Examples?

  14. Structural Pattern • Adapter • Bridge • Composite • Decorator • Façade • Flyweight • Proxy

  15. Adapter • For existing and unrelated classes working in an application that expects classes with a different and incompatible interfaces (Builder?) • Unix process, file system, … Adaptee Client Target implementation Adapter request

  16. Bridge • Inheritance binding (Builder? AbstractFactory?) • Windows (their structure and implementation), Database? Implementor Abstraction IA IB RefinedAbstraction

  17. Composite • Group components Component Leaf Composite

  18. Composite aComposite (is aComponent) aComponent aComponent aComponent aLeaf aComposite aLeaf aComponent aComponent aLeaf aLeaf

  19. Decorator • Specifying the responsibility of certain group, build an transparent interface to component’s client • Teaching, GA, and Instructor Component Leaf Decorator ops DA DB ops ops

  20. Facade • Simplifying interface to more general facilities of subsystems. (AbstractFactory, FactorMethod, Bridge) • Current screen status of Windows? Facade

  21. Flyweight • For sharing resource FlyWeight Client ConcreteFlyWeight

  22. Flyweight aFlyWeight aClient aCF aClient aCF

  23. Flyweight Paragraph and Keys of keyboard?

  24. Proxy • Access control and reference Subject Proxy RealSubject aClient aProxy aRS

  25. Proxy • Network Service?

  26. Behavioral Pattern • Chain of Responsibility • Command • Interpreter • Iterator • Mediator • Memento • Observer • State • Strategy • Template Method • Visitor

  27. Chain of Responsibility • Decouple senders and receivers (sequence? ) • Steps, courses, … Handler aHandler aHandler aHandler

  28. Command • Request, command, …? • Dos/Shell command, file I/O, user interface, …? Invoker Command Receiver ConcreteCommand

  29. Interpreter • Grammar • Composite? • Formal language L=a|bC; C=e|cC. (sample statement: a, b, bc, bcc, …

  30. Iterator • Access without exposing any internal structure • Interface • FactorMethod

  31. Mediator • Distribution of behavior among objects • AbstractFactory Mediator Colleague CC1 CC2 ConcreteMediator

  32. Memento • Record the internal state (checkpoints) • Tests of course, firewall, …? Originator Memento Caretaker

  33. Observer • Maintain consistency • Observer calls Getstatus( ) • Ordering, TCP communication, … Subject Observer ConcreteSubject ConcreteObserver

  34. State • Conditional statements • Used in Command, Memento, Observer, … • Project, study, …, Context State ConcreteStateA ConcreteStateB

  35. Strategy • Builder, Prototype, Bridge, Command, State. • Hollywoodsquare, Chess, searching and sorting (for example, shell), … Context Strategy ConcreteStrategyA ConcreteStrategyB

  36. Template Method • A template method defines an algorithm in terms of abstract operations that subclasses override to provide concrete behavior • Inheritance (generalization), virtual function • Operations (searching and sorting) in Template class (Template Stack, Template Queue). AbstractClass ConcreteClass

  37. Visitor • Packaging related operations from each class in a separate object, called a visitor, and passing it to elements of the abstract syntax tree as it’s traversed. Visitor ConcreteAcceptA ConcreteAcceptB ConcreteVisitorA ConcreteVisitorB ConcreteAcceptA ConcreteAcceptB

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