Scala Interview Practice Questions and Answers are designed to bridge the gap between basic syntax and the high-level architectural patterns required in modern software engineering. I have meticulously crafted this course to cover everything from the transition of Object-Oriented paradigms into pure Functional Programming to the complex world of Type Systems and Metaprogramming. Whether you are preparing for a senior-level interview or aiming to master the Cats and ZIO ecosystems, these practice tests provide deep, technical explanations for every single option to ensure you don't just find the right answer, but truly understand the underlying JVM mechanics and functional principles.

Exam Domains & Sample Topics

Functional Foundations: Pattern matching, tail-recursion, and Scala 3 Extension methods.
The Type System: Covariance, Contravariance, Type Classes, and Higher-Kinded Types.
Concurrency: Akka/Pekko Actor Model, Futures, and Supervision strategies.
Functional Effects: Monads, Functors, and Fiber-based concurrency (ZIO/Cats).
Architecture & Performance: JVM Tuning, SBT security, and Tapir/Http4s APIs.

Sample Practice Questions

Question 1: Which of the following best describes the behavior of a "Context Bound" in Scala 3 (e.g., def find[A: Ordering](list: List[A]))?
- A) It defines a legacy implicit parameter that must be passed manually.
- B) It is a shorthand for a using clause that requires an instance of Ordering[A] to be available in the implicit scope.
- C) It restricts the type A to be a direct subclass of Ordering.
- D) It enables the use of Macros to generate the ordering logic at runtime.
- E) It ensures that the method find can only be called on Numeric types.
- F) It triggers a compiler error if the list is empty.
- Correct Answer: B
- Overall Explanation: Context bounds are a concise way to express that a generic type requires an available type class instance (using/implicit) to function.
- Detail Explanation: * A: Incorrect; while it uses the implicit scope, it is modern syntax, not "legacy" only.
  - B: Correct; [A: Ordering] expands to a hidden (using Ordering[A]) parameter.
  - C: Incorrect; that would be a subtype constraint (A <: Ordering), not a context bound.
  - D: Incorrect; Context bounds are a type system feature, not specifically a Macro trigger.
  - E: Incorrect; it requires an Ordering, which could be for Strings, custom objects, or Numbers.
  - F: Incorrect; type bounds affect compilation, not runtime collection size.
Question 2: In the context of Scala's Variance, if class Box[+A] is defined, which statement is true?
- A) Box[String] is a subtype of Box[Any].
- B) Box[Any] is a subtype of Box[String].
- C) The type A can only be used in "contravariant" positions (method arguments).
- D) This makes the Box class invariant by default.
- E) You cannot use A as a return type for any method in the class.
- F) It requires the use of the opaque keyword in Scala 3.
- Correct Answer: A
- Overall Explanation: The + symbol denotes Covariance, meaning the subtyping relationship of the generic follows the subtyping of the type arguments.
- Detail Explanation: * A: Correct; Since String is a subtype of Any, Box[String] is a subtype of Box[Any].
  - B: Incorrect; this describes Contravariance (-A).
  - C: Incorrect; Covariant types (+A) are generally restricted to "covariant" positions (return types).
  - D: Incorrect; Invariance is the default (no prefix).
  - E: Incorrect; Covariant types are specifically intended to be return types.
  - F: Incorrect; Opaque types are for type masking, unrelated to variance prefixes.
Question 3: When using Akka or Pekko Actors, what happens to an Actor’s state if it encounters an unhandled exception and the default supervisor strategy is applied?
- A) The Actor is permanently terminated and its mailbox is deleted.
- B) The Actor is resumed, and the state remains exactly as it was during the crash.
- C) The Actor is restarted; the current instance is discarded and a new instance is created, resetting the state.
- D) The Exception is bubbled up to the JVM Main thread, crashing the entire application.
- E) The message that caused the error is sent back to the original sender automatically.
- F) The Actor enters a "Stash" mode where it waits for manual intervention.
- Correct Answer: C
- Overall Explanation: The default Supervision Strategy in Akka/Pekko for a standard Exception is Restart.
- Detail Explanation: * A: Incorrect; this is the Stop strategy.
  - B: Incorrect; this is the Resume strategy, which is not the default for generic Exceptions.
  - C: Correct; Restarting creates a fresh instance, meaning internal mutable state is lost.
  - D: Incorrect; Actors are designed for isolation to prevent the whole system from crashing.
  - E: Incorrect; the sender is not notified unless explicitly programmed via "Ask" or status messages.
  - F: Incorrect; "Stashing" is a manual pattern, not a supervisor's automatic response to a crash.

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