🔍 Command vs Strategy

✅ Purpose of Comparison

Both Command and Strategy patterns aim to abstract behavior into interchangeable objects. However, their goals, application contexts, and control flow roles differ significantly. This comparison outlines their structural differences, use cases, and practical design considerations to help choose the right pattern during architectural decision-making.

✅ Comparison Overview

Aspect	Command	Strategy
Purpose	Encapsulate operations as objects	Encapsulate algorithms or behaviors
Usage	Action history, undo/redo, deferred execution	Behavior switching at runtime
Structure	Operation object + receiver + invoker	Strategy interface + concrete strategies
Reusability	Commands are reusable as standalone actions	Strategies are reusable behavior modules
Extension	New actions = new command objects	New behaviors = new strategy classes
Typical Use Cases	GUI actions, batch jobs, undo mechanisms	Payment calculation, sorting strategies

✅ Similarities

• Both encapsulate behavior in objects
• Use common interfaces to unify invocation structure
• Enable decoupling between caller and the actual logic
• Allow behavior replacement via object injection or configuration

✅ Key Differences

Aspect	Command	Strategy
Purpose	Encapsulate actions for invocation, undo, history	Encapsulate algorithms to allow replacement
Responsibility	Represents a request or operation	Represents a behavioral policy
Undo Capability	✅ Yes, via undo()	❌ No built-in support
Invocation Model	Used by an Invoker, often delayed	Used by a Context to delegate execution
Primary Use Cases	Undo/Redo, queues, macros	Payment methods, sorting, formatting, etc.

✅ When to Choose Which

• ✅ Need to store, queue, or redo actions → Command
• ✅ Need to switch processing logic or algorithms → Strategy
• ✅ Want to treat operations as data → Command
• ✅ Want flexible injection of behavior → Strategy

✅ UML Class Diagram

Command Pattern

Strategy Pattern

✅ Practical Tips for Implementation

• ✅ Use Command when actions need to be tracked, queued, or reversed (e.g., text editors, batch jobs)
• ✅ Use Strategy when different policies or behaviors need to be injected at runtime (e.g., payment, logging)
• ▶️ Combination possible: A Command might internally use a Strategy to vary the behavior of the executed action.

✅ Summary

• Command is about representing actions as objects, enabling delayed execution and history management.
• Strategy is about selecting and injecting behavior, promoting algorithm flexibility and configurability.
• Despite similar interface shapes, their design intent differs: one focuses on when and how to execute an operation, the other on which behavior to apply.