Strategy lets the algorithm vary independently from clients that use it The GoF Design Patterns The Strategy Design Pattern Excerpt of the Structure 4
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[PDF] Design Pattern : strategy - Formations en Informatique de Lille
UE Conception Orientée Objet Design Pattern : strategy Intent Define a family of algorithms, encapsulate each one, and make them interchangeable Strategy
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Strategy lets the algorithm vary independently from clients that use it The GoF Design Patterns The Strategy Design Pattern Excerpt of the Structure 4
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Among 23 design patterns, Strategy pattern defines an interface common to all supported algorithms Context uses this interface to call the algorithm defined by a
[PDF] Strategy Design Pattern Strategy is a behaviour design pattern that
Strategy is a behaviour design pattern that is used to encapsulate algorithms designed for a specific task with the ability to change during runtime Strategy lets the algorithm vary independently from clients that use it, which means it decouples the algorithms from the one using the algorithm
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Program to an interface, not to an implementation Favor composition over inheritance Design Principles Page 2 The Strategy Design Pattern
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In this paper, we describe how the Strategy pattern has been recur- sively used to support protocol composition in the BAST framework We also discuss design
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add(new Button(“Press”)); Page 8 Bob Tarr Design Patterns In Java The State and Strategy Patterns
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The paper shows how the Template Method and Strategy design patterns can be used in a program which solves different scheduling problems by means of a
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Strategy Template method Visitor 4 Licence Informatique 3e année – Programmation objet avancée Abstract Factory (1/4) Pattern Abstract Factory :
[PDF] Patterns in C - Part 3: STRATEGY - Adam Tornhill
This part of the series will investigate a design pattern that adds flexibility to common software entities by letting clients customize and extend them without
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|TaskSupporting several kinds of external third-party services for calculating taxes. Supporting several kinds of database connectors. We want to be able to sort different kinds of values.2
|The GoF Design PatternsThe Strategy Design PatternIntent & Example3IntSortHandle "interface»SortHandle
Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.
|Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.The GoF Design PatternsThe Strategy Design PatternExcerpt of the Structure4IntSortHandle
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|The GoF Design PatternsThe Strategy Design PatternGeneral Structure5ConcreteStrategyC "interface»Strategy
Define a family of algorithms, encapsulate each one, and make them interchangeable. |•Subclassing Context mixes algorithm's implementation with that of ContextContext harder to understand, maintain, extend. •When using subclassing we can't vary the algorithm dynamically •Subclassing results in many related classes
They just differ in the algorithm or behavior they employ. •Encapsulating the algorithm in Strategy... •lets you vary the algorithm independently of its context •makes it easier to switch, understand, reuse and extend the algorithmThe GoF Design PatternsThe Strategy Design PatternStrategy - An Alternative to Subclassing6If you would use subclassing instead of the Strategy Design Pattern.
|The Strategy Design PatternExample - "The Strategy Pattern" in Java AWT/Swing7java.awt.Container c = ...; c.setLayout(new java.awt.BorderLayout())public class Container extends Component { ... /** * Sets the layout manager for this container. * @param mgr the specified layout manager */ public void setLayout(LayoutManager mgr) { layoutMgr = mgr; invalidateIfValid(); } /** * Causes this container to lay out its components. ... */ public void doLayout() { LayoutManager layoutMgr = this.layoutMgr; if (layoutMgr != null) { layoutMgr.layoutContainer(this); } } }Client CodelayoutContainer(Container c) : void
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|The GoF Design PatternsThe Strategy Design PatternWhen to use Strategy•...many related classes differ only in their behavior rather than implementing different related abstractions
Strategies allow to configure a class with one of many behaviors. •...you need different variants of an algorithm
Strategies can be used when variants of algorithms are implemented as a class hierarchy. •...a class defines many behaviors that appear as multiple conditional statements in its operations
Move related conditional branches into a strategy.8|The GoF Design PatternsThe Strategy Design PatternThings to Consider•Clients must be aware of different strategies and how they differ, in order to select the appropriate one •Clients might be exposed to implementation issues •Use Strategy only when the behavior variation is relevant to clients9
|The GoF Design PatternsThe Strategy Design PatternThings to Consider•Optional Strategy objects •Context checks if it has a Strategy before accessing it... •If yes, Context uses it normally •If no, Context carries out default behavior •Benefit: clients don't have to deal with Strategy objects unless they don't like the default behavior10
|The GoF Design PatternsThe Strategy Design PatternThings to Consider•Increased number of (strategy) objects •Sometimes can be reduced by stateless strategies that Contexts can share •Any state is maintained by Context, passes it in for each request to the Strategy object
(No / less coupling between Strategy implementations and Context.) •Shared strategies should not maintain state across invocations
(→Services)11|The GoF Design PatternsThe Strategy Design Pattern - Implementation•The Strategy interface is shared by all Concrete Strategy classes whether the algorithms they implement are trivial or complex •Some ConcreteStrategies won't use all the information passed to them
(Simple ConcreteStrategies may use none of it.) (Context creates/initializes parameters that never get used.)If this is an issue use a tighter coupling between Strategy and Context; let Strategy know about Context.12Communication Overhead
|The GoF Design PatternsThe Strategy Design Pattern - Implementation•Giving Strategy Visibility for the Context Information the Strategy needs; two possible strategies: •Pass the needed information as a parameter... •Context and Strategy decoupled •Communication overhead •Algorithm can't be adapted to specific needs of context •Context passes itself as a parameter or Strategy has a reference to its Context... •Reduced communication overhead •Context must define a more elaborate interface to its data •Closer coupling of Strategy and Context13
|The GoF Design PatternsComparison of the Strategy and the Template Design Patterns14ConcreteStrategyC
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Using the strategy pattern, both - the template and the detailed implementations - depend on abstractions (interfaces).
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