Introduction Continued Design Patterns I

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Introduction (Continued)Design Patterns (I)

• Lecture Two

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What is a framework

• Like a class library, but more than an ordinary
  toolkit. The framework components have structural
  and behavioral relations among them.
• Domain specific
• business, telecom, window systems, databases, OS
  kernels,

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What is a framework

• An integrated set of cooperating classes
• architectural design of oo system
• semi-complete application
• set of abstract class are specialized in
  application

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Frameworks

• Inversion of control
• main event loop is often in framework, rather
  than in application code
• hollywood principle dont call us, well call
  you
• code in framework can invoke code in application
  by dynamic binding

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Framework examples

• UI
• model-view-controller (MVC)
• framework for smalltalk user interfaces 1980
• macapp - framework for Mac applications 1986
• Others
• MFC - Microsoft foundation classes
• Choices - operating system framework
• ..

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Patterns vs Frameworks

• Patterns
• reuse of design
• tells you how to do good design
• language independent
• often covers general domains
• addresses small part of a program architecture

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Patterns vs Frameworks

• Framework
• reuse of design and code
• is a design (generic implementation)
• language specific
• often covers specific domain
• addresses overall program architecture

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State Pattern

• Butterfly Example
• Caterpillar
• Chrysalis
• Adult
• Happy/Gloomy Example

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State Pattern

• Book discussion
• Applicability
• state dependent behavior
• large conditional statements
• Scheme structure/participants/collaborations
• Benefits
• extensibility
• make state transitions explicit
• can be shared (flyweight)

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State Pattern

• Implementation
• Who defines state transitions?
• How about table-driven
• Manage lifetime of state objects
• relation with Singleton
• How about use dynamic inhertiance

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Singleton Pattern

• What is it?
• How to implement?

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Homework Digital Watch

• Demo
• Code explained

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Composite Pattern

• Objective treat primitives and containers
  uniformly
• java.awt.
• Example Basket

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Composite Pattern

• Consequences
• recursive composition
• uniform interface
• easier to add new components
• can make design overly general

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Implementation Issues

• Explicit parent references
• Sharing components
• Maximizing the Component interface
• Child management operations
• Who implements a list of components
• Child ordering
• Who should delete components
• Best structures for storing components