Scala Interview Questions & Answers – 15 Most Important

Scala, what started as a general-purpose programming language, is today creating ripples in the Big Data industry – all because of its high scalability factor and ability to handle petabytes Big Data. Scala combines the features of both object-oriented programming and functional programming and can run on JVM (Java Virtual Machine). Along with its vast array of libraries, Scala has emerged to become one of the most preferred programming languages of Developers. The result – increasing demand for Scala experts around the world.

If you wish to take advantage of the growing employment opportunities for Scala experts, the first step will be to ace the Scala Interview. We have designed this post to meet that end – a list of the fifteen most commonly asked Scala interview questions.

Without further ado, let’s get started!

  1. How is Scala is both an OOP and Functional Programming Language?

Scala is a Java-based multiparadigm programming language that treats each value as an ‘object’ that further includes ‘functions.’ This is what makes Scale a combination of both OOP and functional programming languages.

  1. What is the Scala Map?

A Scala map refers to a collection of key-value pairs whose values have to be retrieved using a key. While the values in a map are not unique, the keys are unique.  

  1. What are the different types of Variables in Scala?

There are two types of Variables in Scala:

  • Mutable Variables – These Variables have values that support changes (new values can be assigned to them after their creation). They are declared using the ‘var’ keyword.
  • Immutable Variables – These Variables have values that cannot be changed once created. They are declared using the ‘val’ keyword.
  1. Mention a few frameworks supported by Scala.

The frameworks supported by Scala are:

  • Spark
  • Scalding 
  • Neo4j 
  • Play
  • Akka
  • Lift 
  1. What is Recursion Tail?

In Scala, there’s a function known as Recursion Tail that is capable of calling itself. For instance, function a can call function b that further calls function c. To create a recursive tail, the call back function must be the last performed function.

  1. What purpose do Tuples serve in Scala?

A Tuple’s purpose is to combine a fixed and finite number of items together to allow the programmer/coder to pass a tuple as a whole. Tuples can hold objects with varying data types and are immutable.

  1. What is a BitSet?

A BitSet is a set consisting of non-negative integers depicted as arrays. The arrays vary in size but are compressed into 64-bit words. In a BitSet, the largest number becomes its memory footprint.

  1. What is ofDim()?

In Scala, ofDim() is a function that allows you to create multidimensional arrays. You can store the data in multiple dimensions – it becomes like a matrix of sorts. 

  1. What is the purpose of Closure function?

The closure is a function in Scala whose return value relies on the value of one or more variables that have been declared outside the closure function. 

  1. What is the need for App in Scala?

The App is a helper class in Scale that contains both the main method as well as its members. It can be used to transform objects into executable programs quickly.

  1. What are the types of scopes provided for variables in Scala?

Scala has three scopes for variables according to the use case:

Fields – These are variables that are declared within an object. Depending upon the access modifiers, fields can be accessed anywhere inside the program. They can be declared both as ‘var’ and ‘val.’

Method Parameters – These are immutable variables that are primarily used to pass values to methods. They can be accessed within a method. However, you can also access method parameters from outside the method using a Reference.

Local Variables – These variables are declared within a method, and they can be accessed only from inside a method. 

  1. Explain the difference between the terms “Null,” “Nil,” “None,” and “Nothing.”

Although these terms sound similar, each represents something different.

Null denotes the absence of a value, more particularly the absence of type information for complex types inherited from AnyRef.

Nil refers to the end of a List.

None denotes the value of an option that has no value inside it.

Nothing represents the lowest type – all values under AnyRef and AnyVal fall under it. 

  1. What is a Trait? When is it used?

A Trait denotes a particular unit of Class that facilitates the use of multiple inheritances. It encapsulates a method along with its variables and fields. While a Trait can extend only one Class, a Class can have multiple traits. 

Traits are primarily used for dependency injection. Contrary to Java where dependency injection is accomplished through annotations, Scala has no annotations or no special package that needs to be imported – you only need to initialize the Class with the Trait to trigger the dependency injection.

  1. What is an Implicit Parameter?

Implicit Parameter allows you to invoke a function without passing all the parameters. In this case, you have to provide the default values for all the parameters or those parameters that you want to declare as implicit. To make a value/function parameter/variable ‘implicit,’ you require an implicit keyword.

  1. What is a Monad?

A Monad refers to an object that encapsulates another object. Monad allows you to pass functions to it and also manipulate the encapsulated object’s data.

These 15 questions are some of the most commonly asked and fundamental questions in Scala interviews. Although Scala concepts run deeper than this, we hope this will help you break the ice and prepare for your next Scala interview.

Mayank Sahu

Mayank Sahu is the Program Marketing Manager with upGrad for all emerging technology vertical. His past experience is in analytics industry extensively in healthcare Domain. Mayank has completed his Graduation from IIT Delhi.
Mayank Sahu

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