The Template Method Pattern And The Strategy Pattern Both Ab
The template method pattern and the strategy pattern both abstract some computation in the form of methods. What defining characteristic distinguishes the template method patern from the strategy pattern? Explain your answer.
The template method pattern and the strategy pattern both aim to define algorithms by encapsulating behaviors into methods, but their fundamental distinction lies in their control flow and the degree of framework control. The template method pattern employs a fixed algorithm structure defined in a base class, with some steps delegated to subclasses. This pattern enforces a specific sequence of operations, where the overall skeleton of the algorithm is predetermined, and subclasses merely override certain steps. Conversely, the strategy pattern encapsulates interchangeable behaviors or algorithms within separate classes, and the client code dynamically selects which strategy to use at runtime without a fixed sequence; it promotes composition over inheritance. The key defining characteristic is that the template method pattern fixes the algorithm structure and calls hook methods within that fixed flow, while the strategy pattern provides flexible, interchangeable algorithms that the context can choose to apply at will. This makes the template method more about controlling the sequence of steps, whereas the strategy pattern emphasizes interchangeable behaviors.
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The distinction between the template method pattern and the strategy pattern is rooted in their primary control mechanisms and structural design. The template method pattern is characterized by defining the skeleton of an algorithm within a base class, delegating specific steps to subclasses, and ensuring that the overall sequence remains consistent across different implementations. It emphasizes a fixed control flow where the sequence of operations is predetermined by the base class, which invokes customizable steps through hook or abstract methods. This control over the algorithm's skeleton ensures consistency and enforces a specific process sequence, making subclasses override only particular parts without altering the overall structure.
On the other hand, the strategy pattern emphasizes the encapsulation of interchangeable behaviors or algorithms into separate classes. It facilitates the selection of algorithms at runtime and promotes composition by allowing objects to vary their behavior dynamically. Instead of fixing the sequence of steps, the pattern provides the client with a set of interchangeable algorithms that can be used depending on the context or specific requirements. The core idea is that different strategy objects can be plugged into the context object, changing its behavior without modifying its structure, thereby promoting flexibility and extendibility.
The key difference, therefore, is that the template method pattern imposes a specific control flow over algorithm implementation, ensuring a standard sequence that subclasses can customize. In contrast, the strategy pattern provides a suite of interchangeable algorithms or behaviors that the context object can choose from, emphasizing flexibility over control flow. The template pattern focuses on controlling the structure of an algorithm, while the strategy pattern focuses on encapsulating and exchanging behaviors.
References
- Gamma, E. (1995). Design Patterns in Java. Addison-Wesley.