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Intermediate Topic 24 of 50 Software Engineering

Strategy Pattern

Swapping interchangeable algorithms at runtime.

How it works

The strategy pattern defines a family of interchangeable algorithms behind a common interface and lets the client choose or swap one at run time. The context holds a reference to a strategy and delegates work to it, so behavior varies without conditional statements. In languages with first-class functions, a strategy can simply be a function passed in.

Step-by-step walkthrough

  1. The context holds a reference to a strategy.
  2. Each algorithm implements the same interface.
  3. The context calls the interface method.
  4. It can switch strategies at runtime.
  5. Behavior changes without if/else chains.

Where it is used

Choosing a sorting comparator, payment method, compression algorithm, pricing rule, routing algorithm or validation rule uses strategy. It supports the open-closed principle by adding new strategies without changing the context.

Common pitfall

Too many tiny strategy classes can be overkill for simple branching. Clients must know enough to pick the right strategy. All strategies must honor the same interface contract. If strategies share a lot of code, extract common logic. Use it when you have multiple variations of the same task that change independently.

Where it fits in the course

Strategy Pattern is topic 24 of 50 in Software Engineering, rated Intermediate. It follows Observer Pattern. The next topic is Decorator Pattern.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Software Engineering quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is Strategy Pattern?
Swapping interchangeable algorithms at runtime. It belongs to Software Engineering and is an intermediate-level topic.
Where do people use Strategy Pattern?
Choosing a sorting comparator, payment method, compression algorithm, pricing rule, routing algorithm or validation rule uses strategy.
What is the most common mistake with Strategy Pattern?
Too many tiny strategy classes can be overkill for simple branching.
What should I learn before this topic?
Start with Observer Pattern, the topic just before it in Software Engineering.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Software Engineering quiz.
Is Strategy Pattern hard to learn?
It is an Intermediate topic. Be comfortable with the Beginner topics in this area first, then read the common pitfall carefully, since it is where most mistakes happen.
How long does it take to learn Strategy Pattern?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to Strategy Pattern?
Observer Pattern, Decorator Pattern, Factory Pattern are closely connected. The full list is in the related topics section of this page.
What should I study after Strategy Pattern?
Continue with Decorator Pattern, the next topic in Software Engineering.

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