How does Template Method differ from Strategy?

Template Method uses inheritance, with a base class defining the algorithm and subclasses overriding specific steps, while Strategy uses composition, injecting an entirely swappable algorithm object at runtime rather than customizing a fixed base sequence.

Why is the template method usually marked final?

To prevent subclasses from altering the overall sequence of the algorithm, ensuring only the intended customizable steps can vary while the orchestration logic remains consistent.

What is the Hollywood Principle in this context?

It refers to the base class calling into subclass-provided methods at defined points, rather than subclasses driving the control flow themselves — 'don't call us, we'll call you.'

Is Template Method still relevant in modern, composition-favoring codebases?

It remains useful when a shared algorithmic skeleton is genuinely stable and well understood, though many teams prefer composition-based alternatives for more flexible customization.

Can a subclass override the template method itself?

In a strict implementation it should not, since doing so would defeat the pattern's purpose of preserving a fixed algorithm structure across subclasses.

Programming

Template Method Pattern

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The Template Method pattern is a behavioral design pattern in which a base class defines the overall skeleton of an algorithm as a sequence of steps, while deferring the implementation of one or more individual steps to subclasses, letting…

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Definition

Overview

The Template Method pattern is a classic Gang of Four behavioral pattern built around inheritance. A base (abstract) class defines a method — the 'template method' — that lays out an algorithm as a fixed sequence of calls to other methods, some of which are fully implemented in the base class and some of which are left abstract or given a default implementation intended to be overridden by subclasses. The template method itself is typically marked final (or otherwise discouraged from being overridden), so subclasses cannot change the overall sequence of steps, only the content of individual customizable steps. This pattern is a direct application of the Hollywood Principle — 'don't call us, we'll call you' — because the base class controls the flow, calling into subclass-provided methods at the appropriate points, rather than subclasses driving execution themselves. It is one of the most common ways inheritance is used specifically to share algorithmic structure while allowing variation in details, distinguishing it from patterns like Strategy, which achieves similar customization through composition rather than inheritance. A typical example is a data-processing pipeline: a base class defines a `process()` method that calls `readData()`, `parseData()`, `transformData()`, and `saveData()` in a fixed order, where `readData()` and `saveData()` have generic base-class implementations, while `parseData()` and `transformData()` are abstract methods each subclass must implement for its specific data format. Framework code frequently uses the Template Method pattern — for example, defining a request-handling lifecycle where developers override individual hook methods without needing to reimplement the surrounding orchestration logic. Because it relies on inheritance, the Template Method pattern can lead to fragile hierarchies if overused, and many modern codebases favor composition-based alternatives like Strategy or higher-order functions/callbacks where the language supports them, reserving Template Method for cases where the shared algorithmic skeleton itself is a stable, well-understood abstraction.

Key Concepts

Defines a fixed algorithm skeleton in a base class method
Defers implementation of specific steps to subclasses via abstract or overridable methods
Template method itself is typically not overridden, preserving overall step order
Embodies the Hollywood Principle: base class calls into subclass hooks
Achieves code reuse of shared algorithmic structure via inheritance
Commonly used in frameworks to define extensible lifecycles
Distinguished from Strategy pattern by using inheritance rather than composition
One of the original 23 Gang of Four design patterns

Use Cases

Framework lifecycle hooks (e.g., setup/execute/teardown sequences)

Data import/export pipelines with format-specific parsing steps

Report generation systems with shared layout but variable content sources

Test framework base classes defining setUp/test/tearDown sequences

Build tools defining a fixed build pipeline with customizable steps

Game engines defining update loops with overridable per-entity behavior

Frequently Asked Questions

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