45+ Best Scala Interview Questions You Should Prepare in 2021

45+ Best Scala Interview Questions You Should Prepare in 2021

Whether you are a Scala developer or trying to become one, these Scala Interview Questions & Answers will help you prepare better for your interview.


12 min read

Scala interviews are among the interviews that students dread. The worries, however, are from students who lack confidence. It is therefore advisable to stay away from students or applicants who spread rumors or demotivate you. Therefore, to secure your position as a successful candidate for the Scala interview, prepare yourself with academic learning, prompt replying skills, and a confident smile, which will win the trust of the hiring manager as if you were the best candidate for the job.

Based on research with the interviewees who faced Scala interview questions, it was evident that the majority encountered similar questions. We have gathered 50 of the best Scala interview questions and answers that can help you better understand what you might expect during the interview process.

Currently, Scala is the most popular language based on the Java Virtual Machine, and the number of Scala jobs has increased recently. Therefore, it would be wise to learn Scala with the best Scala tutorials for beginners in 2021.

Scala Interview Questions and Answers For Beginners and Experienced

1. What is Scala?

Answer: Scala is a hybrid programming language based on Java that combines the features of object-oriented and functional-oriented languages. It is used by integration with the Java Virtual Machine and can compile the written code.

2. What are the frameworks supported by Scala?

Answer: Scala supports several frameworks, including the following:

  • Spark
  • Akka
  • Bowler
  • Lift
  • Neo4j
  • Play
  • Scalding

3. What are the different kinds of variables in Scala?

Answer: In Scala, there are mainly two types of variables: Mutable variables and Immutable variables.

4. Explain how Scala is both a Functional and Object-oriented Programming Language.

Answer: Each value in Scala is considered an object, which includes functions as well. As a result, it is a combination of both functional and object-oriented programming.

5. What are the advantages of Scala?

Answer: Following are the advantages Scala offers:

  • Concurrent Programming
  • Concise Code
  • Maintainable
  • Uses Native Tuples codes and Testable codes
  • Singleton objects appear more clearly in the solution compared to static ones.
  • Productive
  • No boilerplate code

6. List the features of Mutable Variables?

Answer: You can declare Mutable variables by using the var keyword. Changing the values of variables is possible even after a variable is declared.

7. List the features of Immutable Variables?

Answer: You can declare immutable variables by using the val keyword. It is not possible to change the values in these variables.

8. What are the different operators in Scala?

Answer: Scala has the following operators:

  1. Arithmetic Operator
  2. Assignment Operator
  3. Bitwise Operator
  4. Logical Operator
  5. Relational Operator

9. Define Stream in Scala?

Answer: It is a lazy list that helps evaluate the elements only when they are needed.

10. What is the advantage of Streams in Scala?

Answer: Streams in Scala are beneficial because they enhance the performance of the program.

11. What is Recursion in Scala? Give an example.

Answer: Scala refers to recursion as the self-referential function. In simple words, it is a function that calls itself.

Example: Recursion occurs in Scala when Function A calls Function B, which calls Function C, etc. The most common use of Recursion occurs in Functional Programming.

12. What are Tuples in Scala?

Answer: In Scala, tuples combine a finite number of items as a set so that the programmer can pass them around as a whole.

13. What is Tail Recursive?

Answer: Tail recursive refers to a callback to the function that should be the end task function.

14. Why do we need App in Scala?

Answer: In other words, the app is a helper class that holds together the method and its members. By using the App trait, we can rapidly convert objects into executable programs quickly. Our classes can extend the app to render the executable code.

15. Explain the scope provided for variables in Scala.

Answer: Three different scopes are depending upon their use. Namely:

  1. Fields: Variables declared inside an object can be accessed anywhere in the program depending on the access modifiers. Var and val can be used to declare fields.
  2. Method Parameters: They are strictly Immutable. Passing values to methods is done primarily with method parameters. Primarily, they are accessed inside a method, but you can also access them from outside the method given by a reference.
  3. Local Variables: They are declared inside a method and are accessible only inside the method. If you return them from the method, you can access them.

16. What are Higher-order functions?

Answer: A higher-order function performs at least one of the following: takes one or more functions as arguments, returns a function as a result.

17. Explain Traits in Scala.

Answer: You can define a trait as a unit that encapsulates a method and its variables or fields. Let's look at an example that will help us understand better.

trait Printable{
   def print()
class A4 extends Printable{
   def print(){
object MainObject{
   def main(args:Array[String]){
      var a = new A4()

18. What is a Closure?

Answer: The closure is a type of function whose return value is dependent mainly on the value of any one or more variables declared outside the closure function. For Example:

1. val multiplier = (i:Int) => i * 10

In the function body, the only variable used is i* 10, i, which is defined as a parameter of the function

19. Explain extend Keyword

Answer: In Scala, you can extend a base class and, you can create an Inherited class in the same way you do in Java utilizing the extend keyword, but there are two restrictions: overriding methods require the override keyword, and only the primary constructor can pass parameters to the base constructor.

20. Mention how Scala is different from Java

Answer: Scala differs from Java in the following scenarios:

  • Values are all treated as objects.
  • Traits
  • Scala supports concurrency.
  • It has DSL support (Domain Specific Language).
  • Scala can support nested functions.
  • It has Type-Inference.
  • Scala supports Closures.

21. What is a Monad in Scala?

Answer: Monads are objects that wrap another object. Instead of manipulating the object directly, you pass the Monad mini-programs, for instance, functions, to perform the data manipulation. Furthermore, Monad decides how to apply the program to the underlying object.

22. How do I Append data in a list?

Answer: You can use ":+" to append data in a list. By using this, you can add a single value to the list. For example:

var a = List.empty[String]
a: List[String] = List()

Use "++" to add one list to another:

a++ = List("mango","banana")

23. How to create Arrays in Scala?

Answer: To create an array, we must declare a variable that references the array and specify the array type. You can create an array as follows:

var z:Array[String] = new Array[String](10)
var z = new Array[Int](5)

24. What is a Scala set? What are methods through which operation can be performed on sets?

Answer: Sets are collections of unique elements (no duplicates). Basically, sets are of two types: mutable and immutable (their value can't be altered). Scala uses immutable sets by default. The following are a few methods for set operations:

  • head: returns the head (first element) of the set
  • tail: returns the entire set, excluding the head element.
  • isEmpty: determines if the set is empty, returns Boolean.

25. Mention the different types of Scala literals?

Answer: In Scala, there are many literals:

  • Boolean literals: true/false
  • Character literals: single character, example: ‘v’, ‘\t’
  • Floating-point literal: Float, example, 1.3
  • Integer literals: Int or Long, example, 12, 0999L
  • String literals: sequence of characters, for example, “Hello, how are you?”
  • Symbol literals: interned strings, for example, 'WHO'.

26. Explain the difference between var and value?

Answer: Var and value are both used to declare variables. Although var represents a variable, its value can be updated later in the code, while val (value) represents a constant or final value that cannot be updated. Upon assigning a value to a var or val, its type cannot be changed.

27. Why Scala prefers Immutability?

Answer: Scala adopts immutability as a design principle, often using it as a default. In the context of Equality and concurrent programs, immutability can be helpful.

28. Why is an Option used in Scala?

Answer: Option in Scala is useful to wraps the Missing value.

29. List the Identifiers in Scala.

Answer: Scala identifiers come in four types:

  1. Alphanumeric identifiers
  2. Literal identifiers
  3. Mixed identifiers
  4. Operator identifiers

30. Explain the ways Scala is better than other programming languages?

Answer: Here are a few reasons why Scala is better than other programming languages are:

  • Works in an environment with a multicore architecture.
  • The addition of third-party libraries is easy with language constructs.
  • Deploys concurrency thereby making synchronization easy.
  • Besides being concise and easy to code, it is also readable, easy to compile, and error-free.
  • Even though Scala is an object-oriented programming language, it also has functional features.

31. Describe Exception Handling in Scala?

Answer: Scala's exception handling is similar to that of Java, except there are no checked exceptions. When throwing exceptions, we use throw new and to catch we can use try{}catch{}blocks. In addition, there is a finally block that executes at the end. WIn the catch block, we can catch multiple exceptions using case ex: blocks.


try {
         val input = new FileReader("myinput.txt")
      } catch {
         case ex: FileNotFoundException => {
            println("File not found")
         case ex: IOException => {
            println("Exception in I/O")
      } finally {
         println("Exiting the code...")

32. Differentiate between Null, Nil, None and Nothing

Answer: Even though they appear similar, but their behaviour differs:

  • Null: It represents the absence of a value.
  • Nil: It denotes the end a List.
  • None: It is the value of an Option with no value.
  • Nothing: It the is lowest type in type System.

33. Explain the functionality of Yield.

Answer: With a loop, Yield produces a value for each iteration. Alternatively, you can do this by using map/flatMap and filter with nomads.

34. What is an Object in Scala?

Answer: In Scala, an object is a specific instance of a class.

35. What is Class in Scala?

Answer: In Scala, a class combines the data and its methods.

36. Is Tuple immutable?

Answer: A tuple is immutable primarily for an Array or List, which can hold objects of different data types.

37. What is the benefit of the App trait? Give an example?

Answer: Using an App trait, objects can be turned into executable programs quickly. We can, for example, extend App to render the executable code.

38. Define implicit classes with syntax in Scala?

Answer: Scala implicit classes with syntax support implicit communication with the class's primary constructor when the class is in scope. It was introduced in Scala 2.10 with the "implicit" keyword.

39. What are Fields in Scala?

Answer: A field is a variable that is declared inside an object. Depending on the access modifiers, they are accessible from anywhere within the program. You can use val and var to declare it.

40. What is a BitSet?

Answer: BitSets are collections of smaller integers represented as bits of a larger integer. In a bitset, we can add multiple items with the '++' operator as we would with a list. Moreover, Bitsets are sets of non-negative integers that are both mutable and immutable.

41. Explain Pattern Matching in Scala through an example

Answer: Pattern matches consist of a series of alternatives, each beginning with the Keyword case. Each alternative includes a Pattern and one or more Expressions, which Scala evaluates when a pattern matches. The arrow symbol => separates patterns and expressions.

42. What is an Auxiliary constructor

Answer: Scala uses an Auxiliary constructor for constructor overloading. Auxiliary constructors must call either previously defined auxiliary constructors or primary constructors in the first line of their bodies.

43. Explain Extractors in Scala

Answer: Extractors in Scala are objects that contain a method called unapply as one of its members. The purpose of the unapply method is to match values and take them apart.

44. Explain Que with example

Answer: The Queue is a Data Structure similar to the Stack, except it follows the First In First Out principle for processing data. To work with queues in Scala, you need to import a library called,

import scala.collection.mutable.Queue

45. What is the result of x+y*z and why?

Answer: Scala follows Presidency and Priority tables like any other programming language. According to the tables, Scala performs the following operations:

  • In Scala, y*z is evaluated first.
  • After that, it adds (y*z) with x.

46. Explain any five string methods.

Answer: Below are a few Scala String Methods:

  • String trim(): Returns a copy of the string, removing leading and trailing whitespace.
  • String toUpperCase: Uses the rules of the specified locale to convert the characters in this String to uppercase.
  • Char[] to CharArray(): Converts this string to a new array of characters.
  • String[] split(String regex): Splits this string around regular expression matches.
  • Int length(): Returns the length of the string.

47. What is the Syntax for function declaration in Scala?

Answer: To declare a function, use the following syntax:

def functionName ([list of parameters]) : [return type] = {
   function body
   return [expression]

48. What are the features of Yield in Scala?

Answer: There are several features of yield, including:

  • It creates value for each iteration.
  • It is used as a Loop.
  • It supports Maps, FlatMaps, Filters, and also Nomads.

49. What are the procedures to compile Scala code?

Answer: In order to compile Scala code, the first step is to write the code in Scala IDE or Scala REPL, which is then converted into the Byte Code for transferring to Java Virtual Machine for compilation purposes.

50. What are the different Loops in Scala?

Answer: Scala has four types of loops:

  • Rather than repeating a statement or group of statements when the condition is true, Loop checks the conditions before executing the Loop body.
  • The Do-While function tests the condition at the end of the Loop body.
  • It helps execute a sequence of statements repeatedly and abbreviates the code that manages in the Loop variable.
  • As a loop control statement, Break terminates the loop statement and transfers execution to that statement following the loop.

If you have made it this far, then certainly you are willing to learn more about Scala. Here are some more resources related to Scala that we think will be useful to you.

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