Scala Interview Questions

Top 50 Scala Question and Answers

The following are the most frequently asked Scala question and answer for experienced and fresher.

1. What is Scala?

Scala is a functional & object-oriented programming language that is designed in such a way that its source code can be executed on Java virtual machine. Scala supports language interoperability which means if a library is written in Scala or Java, it can be referenced directly in Scala or Java programming code. Scala is packed with many functional programming features such as currying, Haskell, pattern matching, lazy evaluation, and so on.

2. How Scala programming language supports both Object-oriented and functional programming style?

Scala considers every single value as an Object including Functions as well that is the reason Scala is a combination of Object-oriented and Functional programming.

3. What kinds of variables are supported by Scala?

There are two types of variables supported by Scala, the first one is Mutable Variables and the second one is Immutable Variables. A Mutable Variables can be declared by using the var keyword and Immutable Variables can be declared by using the val keyword.

4. What are the frameworks supported by Scala?

The following are the lists of framework supported by Scala.

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

5. What is a Queue in Scala?

A Queue is a Data Structure. It is similar to Stack except, it follows the First In First Out procedure for data processing. To use Queue in Scala import this library (import scala.collection.mutable.Queue).

6. What do you understand by an Auxiliary constructor in Scala?

An auxiliary constructor is used for Constructor Overloading. It must call either previously defined auxiliary constructors or primary constructors in the first line of its body.

7. What is Map in Scala?

In Scala, a Map is a collection of key/value pairs, and to fetch a value out of it we can use its key.

8. What is the functionality of the Yield?

Yield produces a value for each iteration and is used with a loop.

9. How is the Scala code compiled?

Scala code gets converted into a Byte code and transferred to the JVM for compilation.

10. What is Option in Scala?

The option is used to Wrap the Missing value.

11. What is Pattern Matching in Scala? Explain through an example.

In Scala, pattern matching is a mechanism to check the value against a tree or the sequence of patterns. The use case of pattern matching is a token sequence that produces matched patterns.

The following is an example that will show how to match against an integer.



    object pattermatchexpmple {
        def main(args: Array[String]) {
            println(matchresult_out(10))
        }
        def matchresult_out(y: Int): String = y match {
            case 0 => "zero"
            case 1 => "one"
            case 2 => "two"
            case _ => "other"
        }
    }

12. What is Exception Handling in Scala?

In a programming language, an exception handling process is used to handle the exception that occurs during the execution of a program. Based on the type of exception(hardware or software) a developer writes a code to handle it.

In Scala, you can use a try/catch block for any exception and perform pattern matching against it using case blocks.

The below example will show exception handling.



	import java.io.FileReader
    import java.io.FileNotFoundException
    import java.io.IOException

    object exceptioncatch_emp {
        def main(args: Array[String]) {
            try {
                val abc = new FileReader("data.xml")
            } catch {
                case ex: FileNotFoundException =>{
                    println("Data file exception, File not found")
                }
                case ex: IOException => {
                    println("File not fund...IO Exception")
                }
            }
        }
    }

13. What are the Loops used in Scala?

The following are three types of loops used in Scala.

For Loop: It is a control flow statement that has two-part, the first part is the iteration and the second part is the body that executes the code.
While Loop: It is a control flow statement that tests the condition first before executing the main body of statements.
Do-While: It is also a control flow statement that executes the body of the statement first then checks the condition.

14. What is the difference between Nil, Null, None, and Nothing?

Let us see the difference between Nil, Null, None, and Nothing.

Null: It represents the absence of a value.
Nil: It represents the end of a List.
None: It represents no value.
Nothing: It represents the lowest type in type System.

15. How many types of Identifiers are there in Scala?

There are four types of Identifiers in Scala.

Literal identifiers
Mixed identifiers
Operator identifiers
Alphanumeric identifiers

16. What are the default Packages in Scala?

There are three default packages in Scala.

Java.lang._
Java.io._
PreDef

17. What are access modifiers available in Scala?

There are three access modifiers available in Scala.

Private: The scope of a private member is restricted to the Class or the Object in which it is declared.
Protected: The scope of a protected member is restricted to Subclasses of the class in which it is declared.
Public: The scope of a public member is available to all.

18. What are the implicit classes in Scala?

An implicit class is a class marked with the “implicit” keyword which allows implicit conversations with the class’s Primary constructor when the class is in scope.

19. Why Scala is different from Java? Give some examples?

Below are some reasons which indicate Scala is different from Java.

Scala has DSL support.
Scala can support Nested functions.
Scala has Type-Inference.
Scala supports concurrency.
Scala supports closures.
In Scala, all values are treated as Objects.

20. What is a Closure in Scala?

The closure is a Function. Its return value is Dependent upon the value of one or more variables that are declared outside of the closure function.

21. What are Higher-order functions in Scala?

Higher-order is a function in Scala that takes one or more Functions as Arguments and returns a function as its result.

22. What is the difference between Class and Objects?

A class is the combination of data and its methods whereas an Object is an Instance in a Class.

23. What are the operators present in Scala?

The following list of operators is supported in Scala.

Arithmetic Operators
Assignment Operators
Bitwise Operators
Logical Operators
Relational Operators

24. What are the advantages of Scala?

The following are some of the advantages of Scala.

Scala has Native Tuples and Concise code.
Scala Arrays use regular Generics.
Scala has no Boilerplate code.
Scala facilitates Concurrent programming.
Scala is highly Maintainable and Productive.
Scala is both Object-Oriented and Functional
Scala is highly Scalable.

25. What are Streams in Scala?

In Scala, streams are lazy in Nature which perform an action when it is needed and this property enhances the performance.

26. What are Extractors in Scala?

An extractor is an object in Scala. It has a method called unapply. Unapply is used to match the value and take it apart.

27. What is the Recursion tail in Scala?

A Recursion is a function in Scala which calls itself. For tail Recursion, the call back to function must be the last function to be performed.

28. What are Tuples in Scala?

In Scala, a tuple can store different types of distinct elements. It is used to returns multiple types of values and immutable in nature.

29. What are the Traits in Scala?

The trait is an object-oriented programming concept that extends a class functionality by using methods. It is identical to the Java interfaces and can't be instantiated.

30. What are Literals in Scala?

A literal is a data that appears directly in the source code. There are many types of literals in Scala such as Integral Literals, Character Literals, Floating-Point Literal, Symbol Literals, Boolean Literals, String Literals, and so on.

Integral Literals
Character Literals
Floating Point Literal
Symbol Literals
Boolean Literals
String Literals

31. What is the Collection in Scala?

Scala collections are containers that hold items such as List, Set, Tuple, Option, Map, and so on. Scala collections are divided between mutable and immutable collections. We can update or extend a mutable collection whereas we can also perform these operations on immutable collections but after that, these operations will return a new collection and don't change the old immutable collection.

32. What is Type Inference in Scala?

In Scala, Type inference is the characteristic of functional programming languages that automatically detect the data type of an expression.

33. What is Named Arguments in Scala?

The Named arguments in Scala refers to the name of the parameter in the function call. In the case of the Named arguments function call, the ordered list of values is provided.

34. What is Case Class in Scala?

In Scala, Case Classes are similar to the general classes in which all parameters are by default public and immutable.

35. What are Generic Classes in Scala?

In Scala, Generic classes take a type as a parameter in square brackets and are used in collection classes.

36. What are Packages in Scala?

In a programming language, a package is a collection of related classes, interfaces, and objects which are grouped in a single name.

37. What are the local variables in Scala?

In Scala, local variables are declared inside a method and accessible from there only.

38. What is Monad in Scala?

In Scala, Monad is a type of object that covers other objects in Scala. If there is any calculation performed on Monad's object then the output will be the input to other calculations step.

39. What is the difference between Scala’s Inner Class and Java’s Inner Class?

Scala’s Inner class is associated with Outer class object whereas Java’s Inner class is associated with Outer class that is Inner class a member of the Outer class.

40. What is Diamond Problem in Scala?

A Diamond Problem is a Multiple Inheritance problem that occurs when a Class extends more than one Traits which have the same method definition.

41. Why Scala doesn’t have a “static” Keyword?

Scala provides support for functional as well as an object-oriented programming language now if we are using a "static" keyword for a class that means we can access the class without creating an object, and this goes against the object-oriented programming language that is why there is no "static" keyword in Scala.

42. What is A Pure Function?

A pure function is a function that returns always the same results irrespective of how many times we call it with the same inputs.

43. What is Range In Scala?

A range is a sequence of integer values and a collection in Scala that is lazy in nature.

44. What are the advantages of functional programming?

The following is a list of functional programming advantages.

It is More Modular.
It is easier to understand Or Easier reason.
It is easier to reuse.
It is less prone to bugs.
It is easier to test.
It is easier to Parallelism and generalizes.

45. Could you share the list of Orm Frameworks Available Use In-Play/Scala Based Applications?

The following is the list of ORM frameworks for Play/Scala-based applications.

Anorm
Slick
SORM
Squeryl

46. Please share the tool name used to persist data in MongoDB NoSQL datastore?

ReactiveMongo driver persists data in MongoDB NoSQL data store and supports fully non-blocking and asynchronous I/O operations.

47. Who all are using Play and Scala to develop their applications?

The following is the list of popular clients who are using Play and Scala actively.

GOV.UK
LuchidChart
Ocado
LinkedIn

48. The tools to develop play and Scala Based Applications?

There are three most popular build tools available to develop Play and Scala Applications.

SBT
Gradle
Maven

49. List out the advantages of using lay/scala Stack for developing web applications?

Below are the major advantages of the Play/Scala stack to develop web applications.

Open-source.
Stateless and easy to develop REST API.
Better error-handling.
High performance and better scalability with reactive.
Highly concurrency and better parallelism.
Better reusability, Easy to test, and more modular
Easy to extend

50. List out the famous Mvc frameworks which support Scala for developing web-based applications?

Below are the most popular MVC frameworks available for Scala Language to develop web applications.

Lift Framework
Spray Framework
Scalatra Framework
Play Framework

Scala Interview Questions Scala - Packages & Imports Scala - Project

Scala - Packages & Imports

Scala - Project