Kotlin Interview Practice Questions and Answers is the ultimate resource I’ve built for developers who want to move beyond basic syntax and truly master the language for high-stakes technical interviews. Whether you are aiming for a mid-level role or a senior position, I have designed these practice tests to challenge your understanding of null safety, functional programming, and the complex world of structured concurrency with Coroutines and Flow. Instead of just memorizing facts, you will engage with scenario-based problems that reflect real-world architectural challenges and JVM performance tuning. By working through these detailed explanations, I ensure you don't just find the right answer, but also understand the "why" behind every line of code, helping you stand out as a candidate who writes clean, safe, and highly optimized idiomatic Kotlin.

Exam Domains & Sample Topics

Language Fundamentals: Null safety, extension functions, and scope functions (apply, let, run).
Functional Programming: Higher-order functions, inline classes, and lazy evaluation with Sequences.
Concurrency & Coroutines: Structured concurrency, Job hierarchy, StateFlow, and SharedFlow.
JVM Internals & Interop: Bytecode optimization, @JvmStatic, reified types, and memory management.
Architecture & Testing: MockK, JUnit 5, Dependency Injection (Koin/Hilt), and Ktor integration.

Sample Practice Questions

Question 1: Which of the following best describes the behavior of crossinline in a higher-order function?
Question 2: In Kotlin Coroutines, what happens if a child job fails when using a SupervisorJob?
- A) All other siblings and the parent job are immediately cancelled.
- B) Only the failing child is cancelled; siblings and the parent continue running.
- C) The parent job is cancelled, but the siblings continue to run until completion.
- D) The application crashes immediately unless a CoroutineExceptionHandler is present.
- E) The SupervisorJob automatically retries the failed child three times.
- F) The failure is ignored and the child remains in an "Active" state.
- Correct Answer: B
- Overall Explanation: Normally, Coroutine cancellation is bidirectional—if a child fails, the parent and all other children fail. A SupervisorJob changes this "scope" so that the failure of a child only affects that specific child. This is essential for UI or server tasks where one failing sub-task shouldn't crash the entire operation.
- Option A Incorrect: This describes a standard Job, not a SupervisorJob.
- Option C Incorrect: If a parent is cancelled, children are always cancelled; this is the opposite of supervision logic.
- Option D Incorrect: While the failure is localized, the exception still needs to be handled, but it doesn't "crash" the parent job itself.
- Option E Incorrect: Kotlin Coroutines do not have built-in "auto-retry" logic based on job types.
- Option F Incorrect: A failed job cannot remain "Active"; it moves to the "Cancelled" or "Completed" state.
Question 3: Which keyword is used to access the underlying property of a delegate from within the class?
- A) thisRef
- B) delegate
- C) field
- D) getValue
- E) by
- F) There is no direct keyword; you must access the property name directly.
- Correct Answer: F
- Overall Explanation: Unlike standard properties where you can use the field identifier inside a custom getter or setter, delegated properties (using the by keyword) do not have a built-in keyword to access the "delegate instance" itself from the owning class. You simply interact with the property name.
- Option A Incorrect: thisRef is a parameter used inside the delegate class definition, not the calling class.
- Option B Incorrect: delegate is not a reserved keyword for property access.
- Option C Incorrect: field is only available in custom accessors for non-delegated properties.
- Option D Incorrect: getValue is the function name the delegate must implement, not a keyword.
- Option E Incorrect: by is the syntax used to assign the delegate, not to access it later.

Welcome to the best practice exams to help you prepare for your Kotlin Interview Practice Questions and Answers.
- You can retake the exams as many times as you want
- This is a huge original question bank
- You get support from instructors if you have questions
- Each question has a detailed explanation
- Mobile-compatible with the Udemy app
- 30-day money-back guarantee if you're not satisfied

I hope that by now you're convinced! And there are a lot more questions inside the course. Enroll today and take the final step toward getting certified!