Top 20 .NET Developer Interview Questions & Answers 🚀 💡 Code Optimization, Performance, & Error-Free Coding Tips!

 

1️⃣ What is code optimization in .NET, and why is it important?

➡️ It’s about making code run faster, use less memory, and reduce bugs—leading to efficient and maintainable projects.

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2️⃣ How do you find performance bottlenecks in .NET apps?

➡️ Use tools like Visual Studio Profiler, JetBrains dotTrace, or Application Insights to spot slow code and fix it early!

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3️⃣ Best data structures for fast data retrieval in .NET?

➡️ Prefer Dictionary for lookups, List for indexed access, and ConcurrentDictionary for thread-safe scenarios.

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4️⃣ Why limit excessive logging in production code?

➡️ Too much logging = slower app + increased costs. Log only what’s essential!

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5️⃣ How does async programming (async/await) boost performance?

➡️ Keeps your app responsive by handling multiple tasks without blocking threads.

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6️⃣ Steps to reduce unnecessary memory allocations?

➡️ Use structs, re-use objects (object pooling), and avoid big objects unless truly needed.

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7️⃣ How do you optimize LINQ queries?

➡️ Combine operations, avoid repeated enumerations, and always filter data at the source (not in-memory).

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8️⃣ When to use caching in .NET?

➡️ Cache expensive or rarely changing data using MemoryCache, Redis, or NCache for instant speed-ups.

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9️⃣ How can exception handling hurt performance, and what’s best practice?

➡️ Avoid exceptions in normal control flow. Use specific try-catch blocks sparingly.

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🔟 What’s Dependency Injection and its key benefit?

➡️ It’s about loose coupling—easier testing, maintenance, and swapping dependencies.

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1️⃣1️⃣ What’s the N+1 query problem in Entity Framework?

➡️ When a loop causes repeated DB calls. Fix with eager loading (Include) or smart projections.

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1️⃣2️⃣ .NET tools for catching memory leaks?

➡️ Visual Studio Diagnostics, JetBrains dotMemory, and the IDisposable pattern help you stay leak-free!

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1️⃣3️⃣ How to minimize network requests?

➡️ Batch where possible, compress, use efficient formats, and stay API-wise.

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1️⃣4️⃣ Why consider DbContext pooling in EF Core?

➡️ Faster request handling by reusing context instances—great for high-traffic services!

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1️⃣5️⃣ When does the JIT compiler NOT inline methods?

➡️ If methods are too big or contain throw statements—keep them small for best performance.

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1️⃣6️⃣ How do you safely refactor for optimization?

➡️ Take small steps, use unit tests, and cut redundant code to keep things maintainable.

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1️⃣7️⃣ Loop and conditional optimization tips?

➡️ Move invariants out, reduce unnecessary iterations, keep function calls minimal inside loops.

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1️⃣8️⃣ Why automate tests and benchmarks?

➡️ Ensure changes don’t break things (tests) and measure performance (BenchmarkDotNet).

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1️⃣9️⃣ Why delete unused code/components?

➡️ It reduces bloat, makes your project safer, and keeps reviews focused!

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2️⃣0️⃣ Best practices for optimizing data access?

➡️ Prefer async for I/O, fetch only what’s needed, filter in SQL, use no-tracking for read-only data.