Applied Design Patterns with Java

Behavioral :: Strategy (315) {C ch 24}

Applicability

Use the Strategy pattern in either of the following cases:

• many related classes differ only in their behavior. Strategies provide a way to configure a class with one of many behaviors.
• there is a need different variants of an algorithm. For example, there is a need to define algorithms reflecting different space/time trade-offs. Strategies can be used when these variants are implemented as a class hierarchy of algorithms.
• an algorithm uses data that clients shouldn't know about. Use the Strategy pattern to avoid exposing complex, algorithm-specific data structures.
• a class defines many behaviors, and these appear as multiple conditional statements in its operations. Instead of many conditionals, move related conditional branches into their own Strategy class.
  

Structure

Participants

• Strategy (Compositor) declares an interface common to all supported algorithms. Context uses this interface to call the algorithm defined by a ConcreteStrategy.
• ConcreteStrategy (SimpleCompositor, TeXCompositor, ArrayCompositor) implements the algorithm using the Strategy interface.
• Context (Composition) is configured with a ConcreteStrategy object, maintains a reference to a Strategy object, and may define an interface that lets Strategy access its data.

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