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Scala Interview Questions

Scala FAQ's

What is Scala?

Scala is a general-purpose programming language that is used for functional and object-oriented programming. It is inspired by the Java programming language and a lot of Java libraries can be used along with Scala. It has high scalability and flexibility. It is statically typed andWhat is meant by Scala Future has the capability to work in a multi-core architecture setting.

How to check Scala version?

To check the version of the Scala the command line has to be used. After navigating to the bin directory where the Scala is installed by using the cd command. Then the version can be seen through the following code:

C:UsersUser>scala -version

Scala code runner version 2.11.6 -- right 2002-2013, LAMP/EPFL

What is the case class in Scala?

A case class in Scala is like a regular class that has a case modifier along with it. This modifier will prevent boilerplate code while programming in Scala. These classes are easy to break down by pattern matching but are not mutable. All the different parameters within the class are immutable. But these classes do not use the new keyword to initialize objects.

What is SBT in Scala?

SBT is a build tool used in Scala to better manage the Scala code. It supports the different Scala test frameworks and helps in the compilation, testing, and deployment of the Scala code. It facilitates the integration of Scala code with the Scala interpreter for better debugging and iteration.

How to implement Sum method in Scala?

A sum method can be implemented in Scala by using a simple function that takes in two parameters and returns their sum. The two parameters can be of int data type and the summation can be stored in a variable that will be returned as a result after the program is executed. The following code has to be used:


What is currying in Scala?

Currying is a technique in Scala that alters the behaviour of a function. It can convert a function that expects two arguments to run, into a function that expects only one argument. This function, in turn, returns another function that will expect the second argument the initial function expected. Therefore, a chain of function calls is generated where each function expects a single argument.

What is a companion object in Scala?

An object that has the same name as that of the class that it belongs to is called a companion object. This object is defined in the same source file where the class is defined. The class of this object is called a companion class. The companion object can have to access to the private fields and private methods of the class.

What is Trait in Scala?

A trait in Scala is used to encapsulate the field and function definitions so they can be reused by combining them with classes. A class can mix with more than one number of traits. They can be considered as collections of abstract methods and can also contain non-abstract methods. Traits are also used for defining object types by mentioning the signature of the methods that support the object.

What is SEQ in Scala?

In Scala, SEQ is a trait that is used to represent sequences that are indexed and non-mutable. It maintains the order of elements as they were inserted. Indexes can be used to access these elements.

Why to choose Scala over Java?

The advantages of Scala over Java are:

  • Scala allows both functional and object-oriented programming whereas Java is the only object-oriented.
  • The code in Scala is more stable and less complicated that can help in the development of applications.
  • It supports asynchronous behaviour that helps in enhancing the functionality of the applications.
  • Scala supports operator overloading but Java does not.
  • Has advanced features for string comparisons, mixins and pattern matching.
  • The code is very scalable which makes it easier to debug and helps in the deployment of applications.

What does => mean in Scala?

The => symbol is used for making instances of functions in Scala, as every function is a class instance.

What is a functor Scala?

A functor in Scala is a type of function that is used to map objects belonging to two categories. If the value is wrapped inside a context, a normal function cannot be applied to it.

How to convert a string to an int in Scala?         

To convert a string to an int in Scala we have to use the toInt method.

How to read a file from HDFS using Scala?      

In bash, an HDFS file can be read through the HDFS API or the following code:

hadoop fs -text /path/to/your/file.gz

How to run Scala jar file?

The SBT in Scala has an SBT package command that allows the creation and execution of an executable jar file. To run that file, the JAR file with a script has to be distributed so that a classpath is built and then it is executed through a Scala command. For this Scala has to be installed in the client system. Another way is to SBT plugin to build a Jar file and execute it using a Java command.

What is Scala future?

Future in Scala plays the role of a placeholder object that holds a value that does not exist yet but will exist in the future. These placeholders help in executing multiple operations in parallel. It can also represent an exception that will be raised if the expected value is not available in the future. Scala combinators such as flatmap, filter and foreach are used to create a Future so that it is non-blocking.

What is Val and Var in Scala?   

Both Var and Val are used for declaring variables in Scala. A var is a mutable variable that is a reference to a value. This variable may be altered. But on the other hand, the val is used to represent a value that is immutable. After assignment of the value, it cannot be changed.

What is Yield in Scala?

Yield in Scala is used for sequence comprehensions that are used along with them for the statement. Using Yields, some data processing and information can be returned after each iteration of the for a loop. For this, the loop body has to be prefixed with the yield keyword.

How to filter the yield result in Scala?     

The yield results in Scala can be filtered through the filter function or the with Filter function.

What is scala try and how to use Scala try?      

Try in Scala is a keyword that is used for exception handling. It represents a code that will either return a value successfully or throw an exception. The instances of Try can be instances of scala.util.Failure or scala.util.Success. For example, if Try is used to perform a division operation on some user inputs, the error handling statements do not have to be put in the code explicitly as try will do it. Try also has the capability to chain or pipeline operations while catching exceptions.

Difference between ‘Null’, ‘Nil’, ‘None’, and ‘Nothing’  in Scala.

Null – It is a trait. null is an instance of the trait Null.

Nil – This is an empty list that has no elements and is of zero length.

None – This represents that no result is obtained after execution of a function. It is used to prevent the null pointer exception.

Nothing – This is a trait that has no instances but is a subtype of everything.        

What is meant by Scala Set?

Scala Set is a collection of paired elements of the same type. There are mutable sets and immutable sets and they do not have duplicate elements.

What is meant by Scala Map?

Scala Maps are collections of Key and Value pairs. Keys are unique, while values are not, and keyes are used to retrieve their corresponding values.

How are values and variables different in Scala?

Values and Variables both hold values in Scala. However, a Value is immutable and once assigned it cannot be changed, while a Variable is mutable and its value can be changed in the program.

What is meant by Recursion Tail in Scala?

Recursion refers to a function that calls itself in the program. When the callback to self is the last performed function, then it is referred to as Recursion Tail.

What is meant by Scala Trait?

Traits in Scala define object types which are specified by the signature of methods that are supported. Traits contain method and field definition and can be reused by mixing these into classes.

What are Case Classes in Scala?

Case Classes are like regular classes except that they can export their constructor parameters. These parameters can be directly accessed as public values.

What is meant by Tupules in Scala?

Tupules group a fixed number of items together to be treated as a single entity. Tupules differ from arrays or lists in that they can contain items of different types and are immutable.

What is the role of the currying in Scala?

Currying is the process of transforming a function taking multiple arguments to a function taking single argument.

What is meant by Monad in Scala?

Class objects are wrapped with a Monad in Scala, giving them two attributes: Identity by ‘unit’ and Binding by ‘flatMap’.

What is meant by Closure in Scala?

Closure is a function whose return value depends on variables declared outside that function.

What is meant by Scala Future?

Scala Future is an object having potential values or future values. It starts a background task and stored values are made available after the task is complete. It also provides different callback functions within itself, making it a complete concurrent class and differing from the Future class of Java which has no inbuilt callback function.

What is the role of Option in Scala?

Option is used to represent the presence or absence of values and may be used to wrap missing values and as replacements to returning null values.

What is meant by Statically Typed Language?

Statically Typed Language is where the Type Checking for errors is done during compilation rather that during runtime. This prevents too many bugs from developing at runtime, keeping the development process easy.

Which is the superclass for all other classes in Scala?

The ‘Any’ class, defined as ‘scala.Any’ is the superclass of all other classes and traits in Scala.

Which is the default Access Modifier of Scala?

The default Access modifier for Scala is public for all class, method, object and trait.

What is meant by Type Inference in Scala?

Type Inference refers to the determination of the type of object, expression, or variable by the compiler during compilation of program.

What is meant by Unit in Scala?

Unit is a final class defined as scala.Unit representing return of No Value or No Useful Value.

What is meant by REPL in Scala?

REPL, pronounced as ‘ripple’ stands for Read Evaluate Print Loop and is an interpreter that executes Scala code from the command prompt.

What is meant by anonymous function in Scala?

Anonymous functions, also called function literals are functions that get instantiated into objects during runtime. These objects are called function values.

What is meant by higher-order function in Scala?

Functions with other functions as parameters and whose results are also functions are called higher-order functions.

What types of identifiers are used in Scala?

Four types of Identifiers used in Scala are Alpha-numeric, Operator, Literal, and Mixed Identifiers.

What is meant by an Implicit Parameter in Scala?

Implicit Parameters defined using the keyword implicit allows functions to run without passing all the parameters.

What is the role of yield keyword in Scala?

The yield keyword when used with an expression, the value from that expression is returned as a collection.

What are the roles of the Apply and Unapply methods?

The Apply method is used to join separate components to create an object. The Unapply method does the opposite and breaks the object apart into its constituents.

How are Array and List different in Scala?

Lists have a recursive covariant mutable data structure, and Arrays have a sequential invariant immutable data structure. In simpler terms, List size can change based on the operations performed on it, while Arrays have a fixed size.