Scala Interview Questions and Answers

Last update: 17 Mar 2022, 30 Questions

Scalable Language, or Scala, is a general-purpose, hybrid functional programming language. Integrating the features of other technical and object-oriented languages, Scala is designed to run on JVM (Java Virtual Machine). This means Scala will enable you to use all the classes of Java SDK, including custom classes, of your Java open source projects. This information is often asked in Scala interview questions. Being used in most of the enterprise-level web apps, Scala provides lightweight syntax that helps developers define anonymous functions. The language supports high-level functions and allows nesting of those functions. Scala will enable developers to write general programming patterns efficiently by reducing the number of lines. This language also empowers the developers to write immutable codes, thus making it easy to apply parallelism and concurrency.

If you are preparing for the Scala language job interview, we have one of the biggest collection of Scala Interview Questions and Answers.

Most Frequently Asked Scala Interview Questions

Here in this article, we will be listing frequently asked Scala Interview Questions and Answers with the belief that they will be helpful for you to gain higher marks. Also, to let you know that this article has been written under the guidance of industry professionals and covered all the current competencies.

1. What is the difference between Java and Scala?
S.no Scala Java
1. Includes implicit Includes widening and casting
2. variables immutable variables mutable by default
3. Pattern matching Switch statements
4. Allows related type to be defined as one file Does not allow related types to be described in one file
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2. What do you mean by Option in Scala and why it is used?

Option in Scala is a container that holds zero or one element of a specific type. It represents values that either exist or do not exist. The Option is used to wrap missing values and is a replacement to return null values. This question has the most likelihood of being asked in Scala interview questions for experienced professionals.

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3. What do you mean by Trait in Scala and when it is used?

A trait in Scala is a unique kind of Class that enables developers to use multiple inheritances. Although a trait can extend to only one class, a class can have many traits. However, unlike classes in Scala, you cannot instantiate traits.

Traits are often used when the user requires dependency injection (DI). In Scala, you do not have annotations or special packages for import. You must initialize the class with trait and dependency gets injected.

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4. What is tail recursion in Scala?

There are times when programmers have to write functions that are recursive, where the critical problem that such functions eat up the entire allocated stack space. To overcome this challenge, Scala provides a “tail recursion” mechanism.

This mechanism optimizes recursive functions so that they do not create new stack space and use the existing stack space.

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5. What is the difference between array and list in scala?
S.no Array List
1. The sequential and mutable data structure The recursive and immutable data structure
2. Invariant Covariant
3. Fixed size Variable size
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6. What is Akka in Scala?

Akka is a runtime and toolkit for building concurrent, fault-tolerant and distributed applications on Java Virtual Machine. Though Akka is written in Scala, it contains language bindings for both Scala and Java. Its approach to handling concurrency is built on Actor Model.

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7. What is the main drawback of Scala language?
Here are some of the limitations of Scala:
  • Online community support is limited.
  • Difficult to learn.
  • Challenge to find professionals for real Scala development.
  • Backward compatibility is limited.
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8. What is REPL in Scala?

REPL in Scala, or Read-Evaluate-Print Loop, is pronounced as ‘ripple.’ It acts as an Interpreter for executing code from the command prompt. This is the reason REPL is called as Scala Command Line Interface (CLI).

The key use of REPL is to develop and test snippets of code for practice purposes. It is useful for Beginner developers to practice low-level programs.

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9. What is the latest version of Scala?

Latest version of Scala is 2.12.11, which was released in March 16, 2020.

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10. What are the advantages of Scala over Java functional programming?
Here are some of the points here Scala scores over other programming languages:
  • Functional Plus OOP language.
  • Allows developers to write reactive apps.
  • Runs on JVM.
  • Cross compatible with Java
  • Cleaner, elegant and more concise code
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11. What are the features of Scala?
These are key features:
  • Type inference
  • Singleton object
  • Immutability
  • Lazy computation
  • Case classes and Pattern matching
  • Concurrency control
  • String interpolation
  • Higher order function
  • Traits
  • Rich collection set
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12. What do you mean by Scala map?

Scala Map is a collection of elements in pairs of key and values, where values can be retrieved using keys. Values are not unique, but the keys are unique. Scala supports two types of maps - mutable and immutable. By default, the language supports the immutable map. You can create a Scala map in two ways – by using comma separated pairs or by rocket operator.

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13. What do you mean by “Type Inference” in Scala?

Type Interface is one of the unique features in Scala that help reduce the amount of coding for developers. Type Interface may be defined as the process used by the compiler to determine the type of value, variable, or return value of a function - based on the statement in which they are found.

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14. Explain the difference between val and var in Scala?
S.no Val Var
1. Refers to value Refers to variable
2. Is constant Is changeable
3. Immutable declaration of variables Mutable declaration of a variable
4. Cannot reassign values once created Reassign values once its created
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15. What is the difference between Function and Method in Scala?
S.no functions methods
1. Defined in Package Defined in a class
2. Can be accessed without objects Cannot be used without an object
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16. Is Scala an OOP?

It is a programming language and it is also an object-oriented programming language like PHP, Java, Python, Ruby, Smalltalk, and others.

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17. What is BitSet in Scala?

A bitset is a collection of non-negative integers that are depicted as arrays in Scala. Variable in size, these arrays are packed into 64-bit words. In a bitset, the most significant number determines the memory footprint.

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18. What do you mean by ofDim in Scala?

It is a method in Scala that allows the developers to create multi-dimensional arrays. We can prepare you for Scala Interview Questions and Answers by informing you of the latest developments.

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19. What are streams in Scala?

Streams are the type of lazy collections, or lazy lists, that get created when starting an element and then generate recursively using the same parts. This feature enhances program performance. Streams are similar to Lists, except that in Streams, the items get added only after being accessed.

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20. What is a monad in scala? Explain

A Monad can be described as an object that wraps another object. In Scala, a class object is covered with a monad. Monads wrap objects and offer two operations - Identity through units, and bind through flatMap.

A Monad determines the best way to apply the program to underlying objects. A lot of recent Scala interview questions were based on this information.

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21. Explain different types of identifiers in Scala?
There are four types of identifiers:
  • Alphanumeric Identifiers: Contain letters, digits, and underscores. Example - myVal.
  • Operator Identifiers: Contain operator characters. Example - +
  • Mixed Identifiers: Contains underscore and an operator identifier. Example - myVar
  • Literal Identifiers: Contain arbitrary string in backticks(`). Example `class.`
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22. What is lambda expression in Scala?

A lambda in Scala is an expression that does not reference value or a variable. Instead, it references an anonymous function. Scala supports lambda expressions in different forms. Developers use lambda expressions because of the convenience, decoupling, and reusability that it provides.

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23. What are higher-order functions in Scala?

Functions in Scala are first-class values. This means that a function can be passed as a parameter or returned as a result. The Higher-order functions in Scala take other purposes as parameters and return a role as a result. This functionality provides flexibility in composing programs.

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24. What is Scala closure?

In Scala, Closure is a function in which the return value of a service is based on the amount of variables, which have been declared outside that function.

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25. What is currying in Scala?

Currying is a way to transform a role with multiple arguments into a series of different tasks with a single discussion each. This feature helps the developers when they are working with higher-order functions.

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26. Explain data types in Scala?

A data type in Scala instructs the compiler about kind of value that needs to be stored in a specific location. In Scala, there are no primitive data types because everything in Scala is treated as an object.

Here are the data types:
  • Byte
  • Short
  • Int
  • Long
  • Float
  • Double
  • Char
  • String
  • Boolean
  • AnyRef
  • Nothing
  • Null
  • Unit
  • Any
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27. Explain Operator and explain types of Operators in Scala?

Operators in Scala are symbols that operate on values. These values are called operands. Operators are essential elements of any programming language, as they allow the developers to perform various types of activities on operands.

This is one of the frequently asked Scala interview questions.

Scala has the following operators:
  • Arithmetic Operators
  • Relational Operators
  • Logical Operators
  • Assignment Operators
  • Bitwise Operators
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28. What do you mean by Foldleft in Scala?

The foldLeft method in Scala is a member of the TraversableOnce trait. Using this method is essential in a recursive function and helps the developers prevent stack-overflow exceptions. This method also allows the developers to specify an initial value.

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29. What is the diamond problem in scala?

The problem of Multiple inheritances in Scala is referred to as the diamond problem. This problem occurs when a Class extends more than one Traits of the same method definition. The inability to decide on the best implementation method to choose leads to Diamond Problem. In Scala, the diamond problem gets resolved through the mechanism of Traits and the class linearization rules.

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30. What is Scala and why it is used?

Scala, is a general purpose, hybrid functional programming language. Integrating the features of other technical and object-oriented languages, Scala is designed to run on JVM. Scala provides lightweight syntax that helps developers define anonymous functions. Scala allows developers to write general programming patterns efficiently by reducing the number of lines. This language also empowers the developers to write immutable codes, thus making it easy to apply parallelism and concurrency.

The unique feature that makes Scala standout from the rest is its ability to scale and expand. It has almost eliminated the common problems associated with other popular languages.

Why it is used?

Scala can be used in many ways, including in android apps, desktop apps, data processing, front-end and back-ends of web applications, Hadoop programs, big data, and data analysis, data streaming, etc.

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Key Features of Scala Language
  • Singleton object
  • Concurrency control
  • Traits
  • Case classes and Pattern matching
  • String interpolation
  • Lazy computation

Classes and inheritance - two features that stand out in object-oriented programming (OOP) language - are supported in Scala. This enables the development and maintenance of modular software. Some other key features include objects, traits, and case classes.

The unique feature that makes Scala standout from the rest is its ability to scale and expand. Considered as one of the “future-proof” languages, it has almost eliminated the common problems associated with other popular languages. Regardless of the nature of the project you are handling, trust Scala to handle it.

Designed to compensate for the faults of Java, JVM views Scala and Java as same languages.

Development History of Scala Language

Martin Odersky started the design process of Scala at the EPFL in Switzerland in 2001. Odersky followed the work dome on Funnel, a programming language that combined ideas from Petri nets and functional programming. After an internal delay, the first version of Scala was publicly released in 2004 on the Java platform.

Latest Version

Latest version is 2.12.8, which was released in Dec 2018. With its first 2.12 release, Scala license got changed to Apache v2.0.

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