Design Pattern

1
Design Pattern

• Dr. Zhen Jiang
• West Chester University
• E-mail zjiang_at_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
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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

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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
Target
Client
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 components
  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

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Chain of Responsibility

• Decouple senders and receivers (sequence? )
• Steps, courses,

Handler
aHandler
aHandler
aHandler
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Command

• Request, command, ?
• Dos/Shell command, file I/O, user interface, ?

Invoker
Command
ConcreteCommand
Receiver
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Interpreter

• Grammar
• Composite?
• Formal language LabC CecC. (sample
  statement a, b, bc, bcc,

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Iterator

• Access without exposing any internal structure
• Interface
• FactorMethod

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Mediator

• Distribution of behavior among objects
• AbstractFactory

Mediator
Colleague
CC1
CC2
ConcreteMediator
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Memento

• Record the internal state (checkpoints)
• Tests of course, firewall, ?

Originator
Memento
Caretaker
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Observer

• Maintain consistency
• Observer calls Getstatus( )
• Ordering, TCP communication,

Subject
Observer
ConcreteSubject
ConcreteObserver
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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 its
  traversed.

Visitor
ConcreteAcceptA ConcreteAcceptB
ConcreteVisitorA
ConcreteVisitorB
ConcreteAcceptA
ConcreteAcceptB