book

Design Patterns

Name: Design Patterns
Author: Christopher G. Lasater
ISBN: 9781449612887

by Christopher G. Lasater

October 2006

Intermediate to advanced

286 pages

4h 36m

English

Jones & Bartlett Learning

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Contents
Introduction
Audience and GoalAssumptions This Book MakesConventions Used in This BookUsing Code Examples
Acknowledgments
1 Why Pattern?
Common Aspects of Object-Oriented LanguagesPatterns Cross-Reference Each OtherRefactoring Legacy Code and Improving New CodeReflection and OOP
2 Creational Patterns
Factory PatternWhat Is a Factory Pattern?Problem 1: Implementation classes with a common base are created in multiple places and no uniformity exists between creational logicSolution 1: Use a factory to encapsulate the class creation code in one placeProblem 2: Class types to be created are determined by immutable logical code and extending the returnable types requires scale modifications to the factorySolution 2a: Replace conditional logic with a class activator, using reflection to determine the needed types for different workflowsSolution 2b: Use abstractions of the factory to determine allowable class types using inheritance (instead of reflection)Comparison to Similar PatternsWhat We Have LearnedRelated PatternsAbstract Factory PatternWhat Is an Abstract Factory Pattern?Problem 1: Different class types need a common interface to a factory method for creation of internal attributesSolution 1: Allow an abstract factory to act as a common base interface for the factories between classesProblem 2: We need to make a builder more extendible to allow different functional processes to occur without changing the builderSolution 2: Use an abstract factory to define common creational methods for the builderComparison to Similar PatternsWhat We Have LearnedRelated PatternsBuilder PatternWhat Is a Builder Pattern?Problem 1: A class needs several operations to create and initialize each of its attributes in an expected order of operations, and each class type instance needs different attribute valuesSolution 1: Use a combination of a director and a builder to encapsulate and uniformly define the processes in the expected order, and use inherited members of the builder to change each type’s reaction to the expected operationsProblem 2: A factory produces classes that need initialization, configuration, data, or state set during creation and this can differ between class types and spans multiple operationsSolution 2: Use registered builders for each class type inside your factory to aid in the initialization of class typesComparison to Similar PatternsWhat We Have LearnedRelated PatternsPrototype PatternWhat Is a Prototype Pattern?Problem: A class that cannot be constructed outside its assembly or package needs a copy made that keeps its current state intactSolution: Create a prototype method on the class to return a cloned instance with its state copied to the needed depthComparison to Similar PatternsWhat We Have LearnedRelated PatternsSingleton PatternWhat Is a Singleton Pattern?Problem: A global class in the application needs to hide its constructor and maintain only one instance of itself while allowing all of its methods to be accessed as instance methodsSolution: Use the Singleton pattern to hide the constructor and maintain an instance of the class inside itselfComparison to Similar PatternsWhat We Have LearnedRelated Patterns
3 Behavioral Patterns
Chain of Responsibility PatternWhat Is a Chain of Responsibility Pattern?Problem: A group of classes each have processes to run in turn, but there is no way to directly determine in which class order each should run its processSolution: Use a chained association of classes that have interdependence on each other to define the order of operationsComparison to Similar PatternsWhat We Have LearnedRelated PatternsCommand PatternWhat Is a Command Pattern?Problem: A document object needs a way to add and store undo and redo actionsSolution: Use a command as the request to store the text and allow the command to handle undo and redo requests of the documentComparison to Similar PatternsWhat We Have LearnedRelated PatternsInterpreter PatternWhat Is an Interpreter Pattern?Problem 1: The format of a date needs to be different depending on the particular type of date expression neededSolution 1: Use an interpreter and expression engine to manage the different date formats by expression typeProblem 2: We need to create classes from metadata from remote packages or assemblies and load them using a common interpreterSolution 2: Allow an interpreter to create the classes from metadata using reflection to recurse into the remote assemblies or packagesComparison to Similar PatternsWhat We Have LearnedRelated PatternsIterator PatternWhat Is an Iterator Pattern?Problem: A list object needs a way to move through each element in the list in consecutive order, retaining the position of the current recordSolution: Create a list iterator that keeps the current record position and has methods to read and move to the next record or to any record in the listComparison to Similar PatternsWhat We Have LearnedRelated PatternsMediator PatternWhat Is a Mediator Pattern?Problem: Message windows reference each other directly, and if new windows are added the code cannot easily manage each window’s reference to the otherSolution: Use a mediator to control messages between each windowComparison to Similar PatternsWhat We Have LearnedRelated PatternsMemento PatternWhat Is a Memento Pattern?Problem: A class needs to have its internal state captured and then restored without violating the class’s encapsulationSolution: Use a memento and a caretaker to capture and store the object’s stateComparison to Similar PatternsWhat We Have LearnedRelated PatternsObserver PatternWhat Is an Observer Pattern?Problem: We have several child forms of an MDI form that we need to inform of changes that occur in the MDI form, and we have no way to do this automaticallySolution: Use the Observer pattern to provide notifications to the child forms when the MDI form state is changedComparison to Similar PatternsWhat We Have LearnedRelated PatternsState PatternWhat Is a State Pattern?Problem 1: We have no way to determine the state of an object without performing calculations outside an objectSolution 1: Use a state object that can change itself as the context object changes to determine the context stateProblem 2: We need to prevent unsynchronized or dirty updates between factory class instantiation callsSolution 2: Make the factory a static interface, and maintain class states across multiple threadsComparison to Similar PatternsWhat We Have LearnedRelated PatternsStrategy PatternWhat Is a Strategy Pattern?Problem: We have a series of algorithmic classes that have no correlation and are not easily exchanged but are needed to do soSolution: Make each class inherit from a common base to provide ease of scalability and exchange between class types so one algorithm class can easily be exchanged for anotherComparison to Similar PatternsWhat We Have LearnedRelated PatternsTemplate PatternWhat Is a Template Pattern?Problem: Shared functionality between classes is desired without copying functionalitySolution: Make both classes inherit from a single base that contains shared functionalityComparison to Similar PatternsWhat We Have LearnedRelated PatternsVisitor PatternWhat Is a Visitor Pattern?Problem: We have a need for a class that encapsulates database transactions and performs specific functions based on the class instance typeSolution: Place each database transaction type in a class that controls that functionality, and use this class to send the data into the databaseComparison to Similar PatternsWhat We Have LearnedRelated Patterns
4 Structural Patterns
Adapter PatternWhat Is an Adapter Pattern?Problem: We wish to allow one class to use another’s methods without using direct inheritanceSolution: Allow an adapter class to hold an instance of the desired class and adapt its methods, properties, and events through the adapter’s methods, properties, and eventsComparison to Similar PatternsWhat We Have LearnedRelated PatternsBridge PatternWhat Is a Bridge Pattern?Problem: We need to allow a class to use functionality from a series of class types without using direct inheritanceSolution: Create a series of classes and allow a bridge class to hold the desired instance of the series and adapt its methods, properties, and events through the bridge’s methods, properties, and eventsComparison to Similar PatternsWhat We Have LearnedRelated PatternsComposite PatternWhat Is a Composite Pattern?Problem: A way is needed to allow a group of classes with a common method and different functionality to work together in sequence without compiling the sequence beforehandSolution: Group each class into a composite, which will manage when each class will have its common method called and will allow manipulation of the sequence of callsComparison to Similar PatternsWhat We Have LearnedRelated PatternsDecorator PatternWhat Is a Decorator Pattern?Problem: We wish to have certain functions associated with a class type only when desired, but not all the timeSolution: We allow a decorator that inherits from the class we are using to take its place and act as the class, but with the increased functionality of the decoratorComparison to Similar PatternsWhat We Have LearnedRelated PatternsFacade PatternWhat Is a Facade Pattern?Problem: We have several classes whose methods make up a process, but we need to control the order in which these classes are called by code outside the assemblySolution: Create a facade layer with interfaces to desired classes that are called in the proper order and allow the subsystem classes to only be called inside the facade assemblyComparison to Similar PatternsWhat We Have LearnedRelated PatternsFlyweight PatternWhat Is a Flyweight Pattern?Problem: A text document uses individual object instances for each character and quickly becomes unwieldySolution: Use shared flyweight objects to instantiate a limited number of character objects that use their current context to change the extrinsic stateComparison to Similar PatternsWhat We Have LearnedRelated PatternsProxy PatternWhat Is a Proxy Pattern?Problem: You have an object in a different domain or server address you would like to access in the current domain, but do not want to allow construction of the object in the local domainSolution: Use a proxy to bridge the two separate domains and allow access between programsComparison to Similar PatternsWhat We Have LearnedRelated Patterns
Glossary of Terms
Index

Overview

Design Patterns demonstrates how software developers can improve the performance, maintainability, portability, and scalability of their code through the use of the Gang of Four design patterns. After a discussion of patterns methodology, reasons for using design patterns, the book delves into each of the 23 patterns. Each pattern section gives a detailed description of the pattern, refactored from either Boolean logic or simpler, less-maintainable code that you might encounter in the real world, and shows readers how to use the pattern in their code. The text walks readers through making the move from current code to the pattern, lists the benefits of using the pattern, and shows how the pattern performs after the refactoring effort, with a goal throughout of providing practical implementations.

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