Strategy Design pattern - Class Diagram

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Understanding the Static Structure of the Strategy Pattern

Before diving into code implementations, visualizing the static architecture through a UML Class Diagram is essential. It provides a blueprint of the relationships between classes, interfaces, and their responsibilities.

In the Strategy Design Pattern, the class diagram shows how object composition replaces inheritance to make algorithms interchangeable.

Core Participants in the Class Diagram

• Strategy (Interface or Abstract Class): Declares an algorithm method signature (e.g., algorithmInterface()) that all supported algorithms must implement.
• Concrete Strategies: Classes such as ConcreteStrategyA and ConcreteStrategyB that implement the Strategy interface with specific behaviors.
• Context: Maintains a reference to a Strategy object via composition/aggregation (has-a relationship) and interacts only through the interface.
• Client: Instantiates the Context and configures it with the desired Concrete Strategy at runtime.

Key UML Relationships

• Realization (Implementation): Concrete strategy classes implement the Strategy interface, shown with a dashed line and open arrow pointing to the interface.
• Aggregation / Association: The Context maintains a reference to the Strategy interface, enabling dynamic replacement of algorithms at runtime.
• Dependency: The Client depends on both the Context and the Concrete Strategy classes to configure the execution pipeline.

Architectural Advantages Reflected in the Diagram

• Adherence to the Open/Closed Principle: New strategy classes can be added without altering the Context class.
• Loose Coupling: Context does not depend on concrete implementations; it relies strictly on the abstract Strategy interface.
• Separation of Concerns: The Context is responsible for business workflows, while individual strategies encapsulate algorithm-specific details.

Related Design Pattern Tutorials to Watch Next

• Strategy Design Pattern: Sequence Diagram Walkthrough
• Strategy Design pattern: Key Points
• Strategy Design Pattern Implementation: Compressing Files

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Strategy Design pattern - Class Diagram

See also:

Strategy Design pattern - Introduction

Strategy Design pattern - Real Time Example [Compress files]

Strategy Design pattern - Real Time Example [Payment]

Strategy Design pattern - Real Time Example [Travel]

Strategy Design pattern - Real Time Example [Sorting]

Strategy Design pattern - Real Time Example [Search]

Strategy Design pattern - Sequence Diagram

Strategy Design pattern - Implementation [Compress files]

Strategy Design pattern - Implementation [Travel]

Strategy Design pattern - Implementation [Payment]

Strategy Design pattern - Implementation [Search]

Strategy Design pattern - Implementation [Sort]

Strategy Design pattern - KeyPoints

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