🔍 Strategy vs Template Method
✅ Purpose of Comparison
The Strategy and Template Method patterns both aim to make a portion of behavior interchangeable.
However, they differ significantly in terms of how the variation is structured, when it is decided, and who controls the flow.
This section clarifies those differences and provides practical guidelines for selecting the right pattern based on context.
✅ Comparison Overview
| Aspect | Strategy | Template Method |
|---|---|---|
| Implementation | Delegation (injecting interface) | Inheritance (subclassing an abstract class) |
| Flexibility | High (can switch at runtime) | Moderate (fixed at class design) |
| Reusability | High (reusable in various contexts) | Lower (tightly coupled with inheritance) |
| Structural Clarity | Clear (explicit via DI) | Less visible (overridden internally) |
| Testability | High (mocks/stubs easily injected) | Moderate (method behavior is fixed) |
✅ Similarities
- Both patterns are used to replace a portion of behavior within a common structure.
- Rely on interfaces or abstract methods to externalize variation.
- Aim to promote maintainability by decoupling "what changes" from "what remains fixed".
✅ Key Differences
| Perspective | Strategy | Template Method |
|---|---|---|
| Variation Mechanism | Injection (composition) | Inheritance (extension) |
| Runtime Switching | ✅ Possible | ❌ Not possible (class is fixed) |
| Client Structure | Just pass a Strategy object | Must define and subclass |
| Control Ownership | Held by caller | Held by base class (flow defined) |
✅ When to Choose Which
- ✅ Need to switch behavior flexibly → Strategy
- ✅ The overall flow must remain fixed → Template Method
- ✅ Want runtime injection or user-defined behavior → Strategy
- ✅ Want to enforce a fixed procedure with minor variations → Template Method
✅ UML Class Diagram
Strategy Pattern
Template Method Pattern
✅ Practical Tips for Implementation
- ✅ Using only Template Method: Ensures a unified structure, but may lead to inflexible and inheritance-heavy designs.
- ✅ Using only Strategy: Offers flexibility but may result in scattered or inconsistent flow control.
- ▶️ Combining both is often ideal: Use Template Method for the procedural flow and Strategy for variable operations (e.g., delivery method).
✅ Summary
Strategy and Template Method are both fundamental patterns for achieving flexible, reusable design.
However, they differ in how they separate variation, when the variation is determined, and where the responsibility lies.
- Choose Strategy for dynamic switching and external control.
- Choose Template Method for enforcing a fixed sequence with customizable steps.
The key is to consider future changes and the flow of control when deciding between the two patterns.