Concept questionMedium~7 min

Interview question

Give practical .NET examples of Strategy, Adapter, and Decorator, and explain how you would choose between them.

Choose Strategy, Adapter, and Decorator for real problems

Selects small structural and behavioral patterns from the problem being solved instead of pattern-name recognition.

1Say itAnswer out loud first

2CompareCompare with Core answer

3RefineRefine with Stronger and Advanced

TL;DR

I might use Strategy for choosing a shipping-price policy, Adapter for presenting a vendor payment SDK as the application's payment port, and Decorator for adding telemetry or caching around an existing implementation. I choose from the design pressure: variable behavior, incompatible interfaces, or cross-cutting behavior around one operation. The class shape can look similar, so intent and contract matter more than the name.

Full answer below

Practice focus

Strategy, Adapter, Decorator, intent, composition, DI registration, and avoiding pattern-driven design.

Answer first

Answer path

Core answer first, then checkpoints toward a stronger answer.

Start
Core answer
Start here. This is the direct spoken answer to practice first.
Why this question matters
The patterns solve different problems. Strategy varies an algorithm, Adapter translates one contract into another, and Decorator wraps the same contract to add behavior.
I might use Strategy for choosing a shipping-price policy, Adapter for presenting a vendor payment SDK as the application's payment port, and Decorator for adding telemetry or caching around an existing implementation. I choose from the design pressure: variable behavior, incompatible interfaces, or cross-cutting behavior around one operation. The class shape can look similar, so intent and contract matter more than the name.
Checkpoint
Stronger answer
Optional upgrade with examples, trade-offs, and sharper phrasing.
A strategy selector should have bounded, validated choices. An adapter owns translation, including errors and provider-specific semantics, rather than leaking them to callers. A decorator preserves the wrapped contract and should be explicit about order when several are composed, such as authorization before caching or telemetry around retries. Dependency injection can assemble these patterns, but registration should remain readable and deterministic.
Finish
Advanced answer
Optional deeper angle for production judgment and nuance.
In production I check semantic compatibility, not just compilation. A caching decorator must preserve authorization and freshness rules. A retry decorator must know whether the operation is idempotent. An adapter cannot pretend a weak provider guarantee is stronger than it is. I keep cross-cutting layers few enough that a trace still explains execution order, and I test the composed pipeline for important cases. I introduce a named pattern when it gives the team a shared model for real variation or translation, not to make ordinary code sound architectural.

Review signals

Use these to catch weak phrasing, shallow reasoning, and risky claims.

Common mistakesCandidateCommon mistakesMistakes that weaken the answer or signal shallow understanding.Open details

Details

Choosing a pattern by class diagram similarity.
Letting adapters leak vendor models.
Composing decorators in accidental registration order.
Using Strategy for unbounded configuration rules.

Red flagsCandidateSigns the design is fragileSignals that an interviewer may treat as risky.Open details

Details

Caching runs before authorization.
Retries wrap a non-idempotent operation blindly.
The adapter changes the meaning of success.
Debugging requires guessing through many wrappers.

Follow-up prompts

Quick interviewer prompts inside this drill.

Follow-up questionsCandidateFollow-up questionsLikely next questions after the main answer.Open details

Details

Treat these as the next interviewer turn. Answer one out loud, then save the gap in your practice notes.

How is Decorator different from middleware?
Where should adapter error translation happen?
How would you test decorator order?

Continue practice

No explicit flow link is set yet, so these are nearby drills from the same path or taxonomy.

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Opening drill

Concept questionMedium~7 min

Interview question

Give practical .NET examples of Strategy, Adapter, and Decorator, and explain how you would choose between them.

Choose Strategy, Adapter, and Decorator for real problems

Selects small structural and behavioral patterns from the problem being solved instead of pattern-name recognition.

1Say itAnswer out loud first

2CompareCompare with Core answer

3RefineRefine with Stronger and Advanced

TL;DR

Full answer below

Practice focus

Strategy, Adapter, Decorator, intent, composition, DI registration, and avoiding pattern-driven design.

Answer first

Answer path

Core answer first, then checkpoints toward a stronger answer.

Start
Core answer
Start here. This is the direct spoken answer to practice first.
Why this question matters
The patterns solve different problems. Strategy varies an algorithm, Adapter translates one contract into another, and Decorator wraps the same contract to add behavior.
I might use Strategy for choosing a shipping-price policy, Adapter for presenting a vendor payment SDK as the application's payment port, and Decorator for adding telemetry or caching around an existing implementation. I choose from the design pressure: variable behavior, incompatible interfaces, or cross-cutting behavior around one operation. The class shape can look similar, so intent and contract matter more than the name.
Checkpoint
Stronger answer
Optional upgrade with examples, trade-offs, and sharper phrasing.
A strategy selector should have bounded, validated choices. An adapter owns translation, including errors and provider-specific semantics, rather than leaking them to callers. A decorator preserves the wrapped contract and should be explicit about order when several are composed, such as authorization before caching or telemetry around retries. Dependency injection can assemble these patterns, but registration should remain readable and deterministic.
Finish
Advanced answer
Optional deeper angle for production judgment and nuance.
In production I check semantic compatibility, not just compilation. A caching decorator must preserve authorization and freshness rules. A retry decorator must know whether the operation is idempotent. An adapter cannot pretend a weak provider guarantee is stronger than it is. I keep cross-cutting layers few enough that a trace still explains execution order, and I test the composed pipeline for important cases. I introduce a named pattern when it gives the team a shared model for real variation or translation, not to make ordinary code sound architectural.

Review signals

Use these to catch weak phrasing, shallow reasoning, and risky claims.

Common mistakesCandidateCommon mistakesMistakes that weaken the answer or signal shallow understanding.Open details

Details

Choosing a pattern by class diagram similarity.
Letting adapters leak vendor models.
Composing decorators in accidental registration order.
Using Strategy for unbounded configuration rules.

Red flagsCandidateSigns the design is fragileSignals that an interviewer may treat as risky.Open details

Details

Caching runs before authorization.
Retries wrap a non-idempotent operation blindly.
The adapter changes the meaning of success.
Debugging requires guessing through many wrappers.

Follow-up prompts

Quick interviewer prompts inside this drill.

Follow-up questionsCandidateFollow-up questionsLikely next questions after the main answer.Open details

Details

Treat these as the next interviewer turn. Answer one out loud, then save the gap in your practice notes.

How is Decorator different from middleware?
Where should adapter error translation happen?
How would you test decorator order?

Continue practice

No explicit flow link is set yet, so these are nearby drills from the same path or taxonomy.

Give practical .NET examples of Strategy, Adapter, and Decorator, and explain how you would choose between them.

Practice focus

Answer path

Why this question matters

Review signals

Follow-up prompts

Continue practice

Give practical .NET examples of Strategy, Adapter, and Decorator, and explain how you would choose between them.

Practice focus

Answer path

Why this question matters

Review signals

Follow-up prompts

Continue practice