Template Method Pattern: Definition and Purpose

Definition
Template Method Pattern is a behavioral design pattern that defines the skeleton of an algorithm in a base class but allows subclasses to override specific steps of the algorithm without changing its overall structure.
This pattern solves the problem of code duplication when multiple classes implement similar algorithms that differ only in certain steps. Instead of repeating the algorithm structure in every class, you define it once in a parent class and let subclasses customize only the parts that vary.
Key Problem Solved: When you have multiple classes performing similar sequences of operations but with slight variations in specific steps, the Template Method Pattern eliminates duplication by extracting the common algorithm structure.
How It Works:
First, you create an abstract base class with a templateMethod() that defines the algorithm's skeleton using a series of method calls. Second, you mark certain methods as abstract (to be implemented by subclasses) while keeping others concrete (shared behavior). Third, subclasses inherit the template method and implement only the abstract steps that require customization.
Interview Tip: Always emphasize that the template method itself should be final (or non-overridable) to prevent subclasses from changing the algorithm structure. Only the hook methods should be customizable.
Real-World Analogy: Think of a recipe template for making beverages. The steps are always the same (boil water, add ingredients, pour into cup, add condiments), but the specific ingredients and condiments differ between tea and coffee. The recipe structure stays constant while the details vary.

💡 Key Takeaways

✓Defines algorithm skeleton in base class, delegates specific steps to subclasses

✓Eliminates code duplication when multiple classes share similar algorithmic structure

✓Template method should be non-overridable to preserve algorithm integrity

✓Subclasses customize behavior by implementing abstract hook methods

✓Follows Hollywood Principle: "Don't call us, we'll call you" (parent controls flow)

📌 Examples

1Beverage preparation system with Tea and Coffee subclasses

2Data processing pipeline with different parsing strategies

3Game AI with different character behaviors following same decision loop

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