Top 25 Scala Interview Questions & Answers in 2020

Attending an interview and wondering what are all the questions and discussions you will go through? Before attending the interview, it’s better to have an idea about the types of Scala interview questions will be asked so that you can mentally prepare answers for them.

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.

To help you out, I have created the top Scala interview question and answers guide to understand the depth and real-intend of Scala interview questions. Let’s get started.

Without further ado, let’s get started!

Top 25 Scala Interview Questions & Answers

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.

2. 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. 

3. Explain why Scala is a hybrid language?

Scala fuses the features of both functional and object-oriented programming languages.  Every value that is input in Scala is treated as an object. Concomitantly, every function is a value. Hence, Scala facilitates every function to be an object. This makes Scala a hybrid programming language.  

4. What are the significant advantages of Scala, in comparison to the existing programming languages?

Scala’s very inception was to upgrade the current cohort of programming languages and add incremental value to popular programming languages like Java, Python, C programming, etc. So, at the very outset, Scala brings in shorter, concise codes that have flexible syntax.

Further, unlike other statically typed programming languages, Scala does not require additional information. For instance, one need not specify the type or have to repeat it at any different stage of the code writing. Scala is integrated into Java Virtual Machine so it can compile any existing codes in Java, so it enables the reuse of codes. 

By virtue of being a hybrid programming language, Scala also supports concurrent programming. Moreover, Scala flags out errors in the codes immediately, so it supports enhanced testing. Overall, it ensures high performance and high productivity. 

Read: Big Data Interview Questions and Answers

5. 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.\

6. Mention a few frameworks supported by Scala.

The frameworks supported by Scala are:

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

7. 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.

8. 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.

9. 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.

10. 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.

11. 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.

12. 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.

13. What are the general access modifiers in Scala?

Private, Protected and Public are the major three access modifiers available in Scala. Each of them has certain salient features. 

The private access modifier limits the access of a user to only the class or the object where the user is defined. 

The protected member may access any Subclass of a Class where the user is defined. 

Unlike the former two, Public members can be accessed from anywhere in the program. Any pre-defined keywords do not restrict access.

14. 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. 

15. How can you run a Scala program?

In order to run a program using Scala, we need first to write it using SCALA REPL and then proceed to compile it. This can be done using the ‘SCALAC’ command to convert it into a Byte code and then transferred to the Java Virtual Machine. Following that, the ‘SCALA’ command can be used to run the program.

Read: Hadoop Interview Questions and Answers

16. 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. 

17. What are the different types of loops in Scala?

Loops are the most common array strings used in Scala. Scala provides four main types of loops:

While Loop- Using a while loop in Scala, users can repeat a statement as long as the condition defined by the “if-else” command holds true. The while loop first tests the condition and then executes it. It comes handy in defining infinite loops. In this case, the condition is set in a way that it doesn’t become false ever. 

Do-While Loop- This loop functions similar to a while loop, with the only exception that the condition is tested at the end of the body of the loop.

For loop-It executes a sequence of statements in a loop body multiple times. For loop is effective in abbreviating the code that manages the loop variable in such cases. 

Break- Unlike the former three, break command is used to terminate a loop immediately after a statement and move it to the execution of the loop. 

18. What are the Presidency and Priority tables in Scala?

The presidency and priority tables determine which operations are to be performed first in Scala.  The following table lays down the operator precedence in Scala. 

For instance, to get the results for p+q*r, Scala will perform the operations in the following order:

First, q*r will be calculated. Then, the value for(q*r) will be added to p to get the final output. 

19. What are the predominant operators in Scala?

Some of the major operators in Scala are Arithmetic operators, Relational operators, Logical operators, Bitwise Operators, and Assignment Operators. The operators in Scala are also referred to as identifiers. 

20. How does a class differ from an object in Scala?

Simply put, an object resides within a class in Scala. A class in Scala combines data and its methods while an object is an instance inside a given class.

21. 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.

22. What are the default packages in Scala?

Scala comes with three default packages, namely Java.lang, java.io, and PreDef. The functionalities of all three packages vary. 

Java.lang is fundamentally a Java programming language. It includes classes that are compatible with the design of the java programming language. 

Java.io helps in importing the classes in Scala for input-output resources. 

PreDef includes type alias for specifically immutable collections like Map, Set, and Lists.

23. 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.

24. How does Scala Option help?

Scala Option keyword comes handy when you’re trying to wrap a missing value.

25. 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.

Conclusion

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.

For further reference, you can also download the PDF version of Scala Interview Questions and Answers mentioned below.

Scala Interview Question and Answers PDF

Mayank Sahu

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