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Design Patterns

by Derek Peacock

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Introduction

Designing OO software is hard Specific enough for current problem General enough for future requirements Experts reuse past design solutions Patterns of classes to solve specific design

problems

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What is a Pattern

A Pattern NameName A ProblemProblem (When to apply the pattern) The SolutionSolution (How to solve the problem)ConsequencesConsequences (Space, time, flexibility,

portability, extensibility)

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Design Patterns

Creational Creating objects

Structural composition of objects

Behavioural Interaction between objects

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Creational Patterns

Abstract Factory

Builder

Singleton

Interface for creating families of related objects

Create complex object from representation

Create a only one globally accessible object

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Structural Patterns

Composite Decorator Façade Proxy

Part-whole hierarchies Attach additional responsibilities Unified interface to subsystems Provide surrogate for object

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Behavioural Patterns

Chain Interpreter

Iterator Memento

Provide a message chain Interpret a language with

grammar Provide access to elements Capture objects internal states