Frequently Asked Scala Interview Questions

Interview Questions Anyone who is into Big Data, Machine Learning, or Data Science, must have come across a language called ‘Scala’. Perhaps while doing Big data online training in Hadoop, one can discover Apache Spark, which is an alternative to Hadoop. This analytics engine called Apache Spark has been written entirely in Scala. So, let us first dive into how Scala was born, and the need for it.

Interview Questions Scala is a high-level programming language, which aims to be both functional as well as an object-oriented language. It is statically typed, meaning variable types are inferred at compile time instead of run time (which is the case for dynamically typed languages like Javascript, Python). Where it mainly differs from JAVA, is Scala doesn’t support primitive types (such as int, boolean, double, etc.) because all data types in Scala are objects, making it purely Object Oriented. It was mainly built to address some of JAVA’s criticisms, such as it being too verbose (requiring too much code for a task) and added features like functional programming, lazy evaluation, and operator overloading.

Why is Knowledge of Scala Important for a Career in Big Data?

If you’re writing an end-to-end data processing pipeline, you have to choose either Hadoop and/or Spark as your framework. While Apache Spark is written entirely in Scala, many more Apache frameworks/services such as Kafka, Samza, and Scalding are partially written in Scala. When it comes to comparing Hadoop and Spark, the latter outperforms Hadoop on both speed and scalability parameters. However, since Spark doesn’t have file storage out of the box, you might have to use an existing HDFS (Hadoop File System) or cloud storage. In most realistic scenarios, Spark would be used along with Hadoop. Since Spark is written in Scala, one can easily pick up the language and use it to write Spark apps, although Spark does support implementations using JAVA, R, and Python.

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Top 10 Scala Interview Questions:

1. Explain Scala

Ans: Scala Interview Questions is a high-level programming language that provides features of both Functional as well as Object-Oriented Programming Languages. Source code written in Scala is compiled to Java bytecode, and the resulting executable code runs on a Java virtual machine. It was released in 2004.

2. What are the types of variables in Scala?

Ans: In Scala, there are primarily two types of variables:

  • Mutable Variables – The values of these variables can be changed after declaration. They are defined using the “var” keyword.

For example:

var name: String = “learnScala”;

  • Immutable Variables – The values of these variables cannot be changed after declaration. They are defined using the “val” keyword.

For example:

val name: String = “learnScala”;

3. How can you implement multiple assignments in Scala?

Ans: If we have a Tuple (a collection of objects of different types), it can be assigned to a “val” variable.

Example: val (var1: Int, var2: String) = Pair (40, “Hello”)

4. Explain classes and objects in Scala.

Ans:  Class – It is a blueprint or prototype using which objects are created.

Object – It is an instance of a class, representing real-life entities.

A sample program to demonstrate class and objects:

// Class with primary constructor

class Car(model:String, year:Int, topSpeed:Int, color:String )


println(“This car is a :” + name + “from” + year);


object Main


// Main method

def main(args: Array[String])


//Creating an object of class Car

var car1= new Car(“Maruti”, 2021, 100, “white”);



5. What are functions? What types can be returned by a function?

Ans: Any group of statements, which perform a particular task can be called a function, it promotes reusability of code. A function can either return a value of a particular data type or return a Unit (which is similar to void in JAVA).

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For example:

a) Function returning an integer

def addInt( a:Int, b:Int ) : Int = {

return a+b


b) Function returning a Unit

def printSomething( ) : Unit = {

println(“Hello World”)


6. What are anonymous functions?

Ans: A function without a name, is called an anonymous function. They can be used to create inline functions.

For example:

var add_func= (a:Int, b:Int) =>a+b // Anonymous function

// Is the same as

def add_func( a:Int, b:Int ) : Int = {

return a+b


7. What are closures?

Ans: Closures are functions whose return value depends on one or more variables defined outside the function, which aren’t passed as arguments to the function.

For example:

val pi = 3.14

// closure.

def area_circle(r:double) = pi*r*r

8. What are arrays and how can you define them?

Ans  An array is a collection of items stored at contiguous memory locations.

Syntax: var data: Array[String] = new Array[String](3) //defined an array

data(0) = “Scala” //Storing values at an index

9. What are collections? List a few types with examples.

Ans: Collections are containers that hold a sequenced linear set of items.

Types: List, Set, Tuple, Option, and Map

For example:

val big_data: List[String] = List(“Hadoop”, “Spark”, “Kafka”) // list

val footballers= Map(7 -> “Ronaldo”, 10 -> “Messi”) // Maps – key/value pairs

10. What are traits?

Ans: A trait is a block of code with fields and methods, which can be reused in classes. They can have method declarations, which can be defined in the class inheriting them. A class can inherit from multiple traits, thereby providing a workaround for achieving multiple inheritances in Scala.

For example:

trait Equal {

def isEqual(x: Any): Boolean


class Point(xc: Int, yc: Int) extends Equal {

var x: Int = xc

var y: Int = yc


def isEqual(obj: Any) = (.x == y )



In conclusion, Scala is a must-learn language for developers who want to work on Big Data, especially the Apache Spark framework. It has ever-growing market demand, with a sea of opportunities in data analytics, data warehousing, machine learning, and many other data-driven technologies.

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