Strategy Design pattern - Sequence Diagram

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Visualizing Object Interactions at Runtime

While class diagrams show the static relationships between classes and interfaces, a Sequence Diagram demonstrates how objects collaborate and exchange messages over time during execution.

In the Strategy Design Pattern, understanding how the Client, Context, and Strategy objects interact in chronological order is key to mastering runtime algorithm delegation.

Step-by-Step Message Flow in the Sequence Diagram

1. Instantiation: The Client instantiates a specific ConcreteStrategy object (e.g., CreditCard, Compression, or Sorting implementation).
2. Context Configuration: The Client creates the Context object and passes the selected strategy instance via constructor or setter method (e.g., setStrategy(strategy)).
3. Business Request: The Client calls the primary operation method on the Context (e.g., context.executeOperation()).
4. Delegation: The Context delegates the call directly to the encapsulated Strategy object by invoking its interface method (e.g., strategy.algorithmInterface()).
5. Return Result: The concrete strategy executes the specific algorithm and returns control or results back to the Context, which forwards the outcome to the Client.

Key Architectural Takeaways from the Diagram

• Decoupled Lifecycles: The context does not instantiate concrete strategies directly; it only receives and delegates to them through an interface contract.
• Dynamic Swapping: At any point during program execution, the client can call a setter method to switch to a different strategy object without destroying or re-instantiating the context.
• Clarity of Responsibility: Each participant has a distinct, single responsibility, making unit testing and maintenance straightforward.

Related Design Pattern Tutorials to Watch Next

• Strategy Design Pattern: Class Diagram Explained
• Strategy Design pattern: Key Points
• Strategy Design Pattern Overview: A Beginner's Introduction

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Strategy Design pattern - Sequence 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 - Class 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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