Scala Interview Questions and Answers
Experienced / Expert level questions & answers
Ques 1. What is the 'for' comprehension in Scala?
The 'for' comprehension is a syntactic sugar for combining sequences of 'map', 'flatMap', and 'filter' operations. It makes code more readable and expressive.
Ques 2. How does Scala support concurrency?
Scala provides actor-based concurrency using the Akka library. Actors are lightweight, concurrent entities that communicate through message passing.
Ques 3. Explain currying in Scala.
Currying is the technique of transforming a function that takes multiple arguments into a series of functions that take one argument each. It is supported natively in Scala.
Ques 4. What is type inference in Scala?
Type inference is the ability of the Scala compiler to automatically deduce the data types of expressions, making it unnecessary to explicitly specify types in most cases.
Ques 5. How are implicits used in Scala?
Implicits are used for automatic type conversions, adding new methods to existing classes, and resolving ambiguities. They are a powerful and controversial feature in Scala.
Ques 6. What is the 'Future' class in Scala?
The 'Future' class represents a value or error computation that may be running asynchronously. It is commonly used for handling concurrent and parallel programming.
Ques 7. Explain the concept of variance in Scala.
Variance is a way to express how subtyping between more complex types relates to subtyping between their components. It is denoted by the use of 'covariant', 'contravariant', or 'invariant' keywords.
Ques 8. What is tail recursion optimization in Scala?
Tail recursion optimization is a compiler optimization that eliminates the overhead of function calls when the last action of a function is a call to itself (tail call). Scala supports this optimization for tail-recursive functions.
Ques 9. Explain the concept of implicits in Scala.
Implicits are a mechanism in Scala that allows the compiler to automatically insert extra arguments, convert types, or provide default values. They are used for concise and flexible programming.
Ques 10. What is the 'implicitly' method in Scala?
The 'implicitly' method is used to summon an implicit value of a given type. It is often used in implicit conversions and parameter injection.
Ques 11. Explain the 'self' type in Scala.
The 'self' type is a way to declare the type of 'this' within a class or trait. It is often used in situations where the type of 'this' needs to be specified explicitly.
Ques 12. Explain the concept of covariance and contravariance in Scala.
Covariance allows a type parameter to vary in the same direction as the container type, while contravariance allows it to vary in the opposite direction. They are denoted by + and - symbols, respectively.
Ques 13. Explain the 'yield' keyword in the context of Scala futures.
In the context of Scala futures, 'yield' is used within a 'for' comprehension to produce a value that will be included in the future's result. It is often used for combining and transforming asynchronous computations.
Ques 14. What is the purpose of the 'implicit class' feature in Scala?
The 'implicit class' feature in Scala allows developers to add new methods to existing classes without modifying their source code. It is often used to extend functionality in a clean and concise manner.
Ques 15. What is the purpose of the 'implicit parameter' in Scala?
An implicit parameter is a parameter marked with the 'implicit' keyword. It allows the compiler to automatically provide a value for the parameter if there is an implicit value of the corresponding type in scope.
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