Top 30 Interview Questions on Scala

1.What is Scala and what are its main features?

Scala is a general-purpose, statically typed programming language designed to be concise and expressive. Its main features include functional programming support, strong static typing, interoperability with Java code, and an expressive syntax.

2. What are the differences between Scala and Java?

Scala is a more concise and expressive language than Java, with a syntax that is closer to natural language. It also has more advanced features for functional programming, such as support for immutability and higher-order functions. Scala also has better support for concurrency and parallelism than Java.

3.What is the relationship between Scala and the JVM?

Scala is designed to run on the Java Virtual Machine (JVM) and is fully interoperable with Java code. This means that Scala code can call Java code and vice versa, and that Scala programs can run on any platform that supports the JVM.

4.What is a trait in Scala?

A trait is a construct in Scala that defines a set of methods and fields that can be reused in multiple classes. Traits can be thought of as a mix-in of behavior to classes, and they provide a way to achieve multiple inheritance in Scala.

5.What is a higher-order function in Scala?

A higher-order function is a function that takes one or more functions as arguments or returns a function as its result. Higher-order functions are a key feature of functional programming and allow for greater flexibility and expressiveness in code.

6.How is concurrency handled in Scala?

Concurrency in Scala is typically handled through the use of actors and message passing. Actors are lightweight threads that communicate through messages, and they provide a simple and powerful model for concurrent programming.

7.What is the difference between a var and a val in Scala?

In Scala, a var is a mutable variable, meaning that its value can be changed after it is defined. A val, on the other hand, is an immutable variable, meaning that its value cannot be changed after it is defined.

8.What is an implicit in Scala?

In Scala, an implicit is a value that is automatically provided to a method or function. Implicits are typically used to provide default values or to convert between types.

9. What are the advantages of using Scala over Java?

Scala offers several advantages over Java, including a more expressive syntax, better support for functional programming, better support for concurrency, and greater flexibility and expressiveness in code.

10.What is the difference between an abstract class and an interface in Scala?

In Scala, an abstract class is a class that cannot be instantiated and is designed to be subclassed. An interface, on the other hand, is a type that defines a set of methods that a class must implement. Interfaces in Scala can also contain fields and concrete methods, unlike in Java.

11.What is a case class in Scala?

A case class is a class that is designed to be used in pattern matching. Case classes are immutable by default, and they automatically generate equality and hash code methods.

12.How are collections handled in Scala?

Collections in Scala are handled through a hierarchy of collection traits and classes, including Seq, Set, and Map. Scala’s collections support both mutable and immutable versions, and they offer a wide range of methods for transforming and manipulating data.

13.What is pattern matching in Scala?

Pattern matching is a powerful feature of Scala that allows you to match a value against a set of patterns and execute code based on the match. Pattern matching is commonly used with case classes and collections.

14.What is a closure in Scala?

A closure is a function that captures and retains references to values from its surrounding environment. Closures are a key feature of functional programming and allow for greater flexibility and express

15.Write a few Frameworks of Scala

Some of the Frameworks supported by Scala are as follows:

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

 16.Mention the types of Variables in Scala? And What is the difference between them?

The Variables in Scala are mainly of two types:

Mutable Variables

We Declare Mutable Variables by using the var keyword.

The values in the Mutable Variables support Changes

Immutable Variables

We declare Immutable Variables using the val keyword.

The values in Immutable Variables do not support changes.

17. Explain Streams in Scala.

In simple words, we define Stream as a Lazy list which evaluates the elements only when it needs to. This sort of lazy computation enhances the Performance of the program.

18. Mention the Advantages of Scala

Some of the major Advantages of Scala are as follows:

  • It is highly Scalable
  • It is highly Testable
  • It is highly Maintainable and Productive
  • It facilitates Concurrent programming
  • It is both Object-Oriented and Functional
  • It has no Boilerplate code
  • Singleton objects are a cleaner solution than Static
  • Scala Arrays use regular Generics
  • Scala has Native Tuples and Concise code 

19. Explain the Operators in Scala

The following are the Operators in Scala:

  • Arithmetic Operators
  • Relational Operators
  • Logical Operators
  • Bitwise Operators
  • Assignment Operators

20. What is Recursion tail in Scala?

Recursion’ is a function that calls itself. For example, a function ‘A’ calls function ‘B’, which calls the function ‘C’.  It is a technique used frequently in Functional programming. In order for a Tail recursive, the call back to the function must be the last function to be performed.

21. Explain the use of Tuples in Scala?

Scala tuples combine a Finite number of items together so that the programmer can Pass a tuple around as a Whole. Unlike an Array or List, a tuple is Immutable and can hold objects with different Datatypes.

22. How is a Class different from an Object?

 Class combines the data and its methods whereas an Object is one particular Instance in a class.

23. Why do we need App in Scala?

App is a helper class that holds the main method and its Members together. The App trait can be used to quickly turn Objects into Executable programs. We can have our classes extend App to render the executable code.

123object Edureka extendsApp{     println("Hello World")   }

24. What are Higher-order functions?

Higher-order function is a function that does at least one of the following: takes one or more Functions as Arguments, returns a Function as its result

25. Explain the scope provided for variables in Scala.

There are three different scopes depending upon their use. Namely:


  • Fields are variables declared inside an object and they can be accessed anywhere inside the program depending upon the access modifiers. Fields can be declared using var as well as val.

Method Parameters:

  • Method parameters are strictly Immutable. Method parameters are mainly used to Pass values to the methods. These are accessed inside a method, but it is possible to access them from outside the method provided by a Reference.

Local Variables:

  • Local variables are declared inside a method and they are accessible only inside the method. They can be accessed if you return them from the method.

26.What is a Closure?

A Closure is considered as a Function whose return value is Dependent upon the value of one or more variables declared outside the closure function.


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

Here the only variable used in the function body, i * 10 , is i, which is defined as a parameter to the function

27.Explain Traits in Scala.

 A Trait can be defined as a unit which Encapsulates the method and its variables or fields. The following example will help us understand in a better way.

1234567891011121314trait Printable{   def print()}classA4 extendsPrintable{   def print(){      println("Hello")  }}object MainObject{   def main(args:Array[String]){      var a = newA4()      a.print()  }}

28. Mention how Scala is different from Java

A few scenarios where Scala differs from Java are as follows:

  • All values are treated as Objects.
  • Scala supports Closures
  • Scala Supports Concurrency.
  • It has Type-Inference.
  • Scala can support Nested functions.
  • It has DSL support [Domain Specific Language]
  • Traits

29. Explain extend Keyword

You can extend a base Scala class and you can design an Inherited class in the same way you do it in Java by using extends keyword, but there are two restrictions: method Overriding requires the override keyword, and only the Primary constructor can pass parameters to the base Constructor. Let us understand by the following example

123456789println("How to extend abstract class Parent and define a sub-class of Parent called Child")  classChild=(name:String)extendsParent(name){     override def printName:Unit= println(name)  } object Child {  def apply(name:String):Parent={  newChild(name)  }}

30.Explain implicit classes with syntax

Implicit classes allow Implicit conversations with the class’s Primary constructor when the class is in scope. Implicit class is a class marked with the “implicit” keyword. This feature was introduced in with Scala 2.10 version.

123456//Syntax:  object {      implicit classData type) {          def Unit = xyz       }  }
Top 30 Interview Questions on Scala
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