Top Thirty Scala As Well As Functional Programming Interview Questions As Well As Answers

Scala is a programming linguistic communication which aims to render best of both object-oriented programming in addition to functional programming world. It non exclusively allows you lot to  build elegant shape hierarchies for maximum code reuse in addition to extensibility but also allows you lot to implement their demeanor using higher-order functions in addition to other functional programming technique. It is touted every bit 1 of the languages which tin sack in all probability take away hold over Java, though it didn't tumble out particularly after Java 8 unloose which also provides about functional programming tools to Java e.g. lambda expression in addition to stream. Nevertheless, Scala is a skilful linguistic communication in addition to created past times next best practices from several other programming languages including Java. Scala is an acronym for “Scalable Language”. This agency it is designed past times keeping scalability inwards mind. Many companies e.g. Twitter, LinkedIn, in addition to Intel uses it for their mission-critical application.

One of the key trace of Scala is its concise syntax in addition to less ceremony i.e. it is way less verbose than Java. You tin sack write less in addition to do to a greater extent than because the Scala compiler is doing a lot of piece of work for you lot in addition to that's why many developers also exercise Scala every bit a scripting language. Though, for some, it agency Scala is less readable than Java. You can't laid everyone happy.

Another dandy thing close Scala is that it offers a overnice mix of object-oriented in addition to functional programming concepts. The linguistic communication back upwards shape in addition to every value is an object in addition to every functioning is a method call.  Many mutual object oriented blueprint patterns inwards other languages take away hold built-in back upwards for Scala. For example, Singleton pattern is supported through object definitions in addition to Visitor pattern is supported through pattern matching.


On the other hand, Scala is also a full-blown functional language. It has everything you lot would appear from a functional programming linguistic communication similar Haskel or Lisp e.g. fantabulous functions, a library with efficient immutable information structures, in addition to a full general preference of immutability over mutation.

One to a greater extent than dandy thing close Scala is that it laid total exercise of mature Java resources, it allows you lot to exercise Java libraries inwards Scala project. Scala code is compiled into a bytecode which tin sack live understood past times JVM in addition to past times using implicit classes, Scala fifty-fifty allows you lot to add together novel operations to existing classes, no thing whether they come upwards from Scala or Java.

With the manufacture adoption of Apache Spark, a leading Scala framework for cloud computing in addition to Big Data, Scala has rapidly expire pop alongside Big Data professionals. If you lot are going for an interview for whatsoever of the Big Data chore openings that require Apache Spark sense so you lot should prepare for Scala interview questions every bit good because Spark is written inwards Scala.

In this article, I am going to portion about primal Scala linguistic communication in addition to Functional Programming questions which are useful for both Java in addition to Big Data professional, both newcomers in addition to experienced programmers. There is also a skilful demand for Scala developers on startups every bit Scala programmers are rattling less every bit compared to Java professionals in addition to they are also considered best programmers, thank you lot to the hard learning curvature of Scala. They are also fetching rattling skilful salaries, somewhere inwards the gain of $100K to $120K, depending on your science in addition to experience.

Scala Interview Questions in addition to Answers

Here is my listing of about xx strange questions from Scala programming in addition to linguistic communication inwards general. These are collected from diverse sources including friends in addition to colleagues. It is to a greater extent than often than non for Java developers who are learning Scala or take away hold about sense working inwards Scala, looking for evolution chore inwards Scala. Since the demand of Scala developer is on the rise, with preference to experienced Java programmers, you lot could exercise this listing to prepare for telephonic in addition to screening circular of interviews.


What is the latest version of Scala?
This is a uncomplicated inquiry to banking concern check whether you lot maintain yourself up-to-date with the latest information close Scala or not. If you lot take away hold non been using Scala actively in addition to don't know the reply so you lot tin sack say that you lot take away hold used sure Scala version. Though, the electrical flow version of Scala is Scala 2.12, which also require Java 8. Older Scala versions are compatible with Java vi in addition to above.


Who is the writer of Scala Programming language?
This is about other basic inquiry close Scala to banking concern check your full general cognition close Scala. It is designed past times Martin Oderskey, a German linguistic communication reckoner scientist. He also teaches a course, Functional Programming Principles inwards Scala in addition to Functional Program Design inwards Scala on Coursera.

What is the departure betwixt val in addition to var inwards Scala?

The val keyword stands for value in addition to var stands for variable. You tin sack exercise keyword val to shop values, these are immutable, in addition to cannot alter 1 time assigned. On the other hand, keyword var is used to create variables, which are values that tin sack alter after beingness set. If you lot endeavour to modify a val, the compiler volition throw an error. It is similar to the final variable inwards Java or const inwards C++.

What is the departure betwixt == inwards Java in addition to Scala?

Scala has to a greater extent than intuitive notion of equality. The == operator volition automatically run the instance's equals method, rather than doing Java vogue comparing to banking concern check that 2 objects are genuinely the same reference. By the way, you lot tin sack yet banking concern check for referential equality past times using eq method. In short, Java == operator compare references patch Scala calls the equals() method. You tin sack also read the departure betwixt == in addition to equals() inwards Java to acquire to a greater extent than close how they acquit inwards Java, here.

How to you lot create Singleton classes inwards Scala?

Scala introduces a novel object keyword, which is used to stand upwards for Singleton classes. These are the shape with just 1 instance in addition to their method tin sack live idea of every bit similar to Java's static methods. Here is a Singleton shape inwards Scala:

package assay  object Singleton{   def sum(l: List[Int]): Int = l.sum }

This total method is available globally, in addition to tin sack live referred to, or imported, every bit the test.Singleton.sum. A singleton object inwards Scala tin sack also extend classes in addition to traits.


Which books you lot take away hold read on Scala so far?
This is a full general inquiry to banking concern check how did you lot acquire Scala, did you lot read mass or documentation or tutorial etc. It's best to advert the mass you lot take away hold read on Scala e.g. I take away hold read Programming inwards Scala by Martin Odersky in addition to Functional Programming inwards Scala 1st Edition past times Paul Chiusano. If you lot take away hold non read whatsoever mass so just say you lot take away hold non read whatsoever mass yet in addition to similar to read Scala documentation or planning to read a mass etc. The most of import thing is, to live honest, don't advert a mass if you lot take away hold non read it yet. On a dissimilar note, endeavour reading a skilful mass on Scala, Martin Odersky's Programming inwards Scala: Updated for Scala 2.12 is a skilful starting point.

Which keyword is used to define a business office inwards Scala?

H5N1 business office is defined inwards Scala using the def keyword. This may audio familiar to Python developers every bit Python also uses def to define a function.

What is the exercise of App shape inwards Scala?

Scala provides a helper class, called App, that provides the main method. Instead of writing your ain principal method, classes tin sack extend App shape to make concise in addition to executable applications inwards Scala every bit shown inwards the next example:

object Main extends App {   Console.println("Hello Scala: " + (args aString ", ")) }

Here, object Main inherits the principal method of App trait in addition to args returns the electrical flow command work arguments every bit an array, similar to String[] args inwards Java principal method.


What's the departure betwixt the next terms in addition to types inwards Scala: 'Nil', 'Null', 'None', in addition to 'Nothing' inwards Scala?
Answer: Even though they appear similar, at that spot are about subtle differences betwixt them, let's run into them 1 past times one:

• Nil represents the destination of a List.
• Null denotes the absence of value but inwards Scala, to a greater extent than precisely, Null is a type that represents the absence of type information for complex types that are inherited from AnyRef. It is dissimilar than null inwards Java. 
• None is the value of an Option if it has no value inwards it.
• Nothing is the bottom type of the entire Scala type system, incorporating all types nether AnyVal in addition to AnyRef. Nothing is commonly used every bit a render type from a method that does non terminate unremarkably in addition to throws an exception

What is the departure betwixt an object in addition to a shape inwards Scala?
An object is a singleton instance of a class. It does non demand to live instantiated past times the developer. If an object has the same advert that a class, the object is called a companion object.


What is the departure betwixt a trait in addition to an abstract shape inwards Scala?
Here are about key differences betwixt a trait in addition to an abstract shape inwards Scala:

• A shape tin sack inherit from multiple traits but exclusively 1 abstract class.
• Abstract classes tin sack take away hold constructor parameters every bit good every bit type parameters. Traits tin sack take away hold exclusively type parameters. For example, you lot can’t say trait t(i: Int) {}; the i parameter is illegal.
• Abstract classes are fully interoperable with Java. You tin sack telephone telephone them from Java code without whatsoever wrappers. On the other hand, Traits are fully interoperable exclusively if they do non comprise whatsoever implementation code. See hither to acquire to a greater extent than close Abstract class inwards Java in addition to OOP. 

What is the departure betwixt a call-by-value in addition to call-by-name parameter?
The principal departure betwixt a call-by-value and a call-by-name parameter is that the onetime is computed earlier calling the function, in addition to the after is evaluated when accessed.

What is the instance shape inwards Scala?

H5N1 instance shape is a special shape definition, which plant just similar a regular Scala shape but compiler creates equals() in addition to toString() methods, every bit good every bit immutable access to the plain of the class. You tin sack build instance shape instance without using the new keyword. One to a greater extent than do goodness of the instance classes is that instances tin sack live decomposed into their constructed fields in addition to tin sack live used inwards pattern matching. Here is an illustration of instance shape hierarchy inwards Scala, which consists of an abstract super shape Vehicle in addition to 2 concrete instance classes Car in addition to Bike

abstract class Vehicle case class Car(brand: String) extends Vehicle case class Bike(brand: String, price: long) extends Vehicle

Instantiating a instance shape is slow because you lot don’t demand to exercise the novel keyword

val myCar = Car("BMW")

The constructor parameters of instance classes are treated every bit public values in addition to tin sack live accessed straight e.g. myCar.brand volition give you lot "BMW".

Here is about other illustration of traits inwards Scala using instance classes:

What is the departure betwixt a Java method in addition to a Scala function?

Scala business office tin sack live treated every bit a value. It tin sack live assigned to a val or var, or fifty-fifty returned from about other function, which is non possible inwards Java. Though Java 8 brings lambda appear which also makes business office every bit a start shape object, which agency you lot tin sack transcend a business office to a method just similar you lot transcend an object every bit an argument. See here to acquire to a greater extent than close the departure betwixt Scala in addition to Java.


What is the departure betwixt a Java hereafter in addition to a Scala future?
Even though both Java in addition to Scala's Future object provides asynchronous computation, but at that spot is a subtle departure betwixt them on how you lot retrieve the effect of the computation. Java's Future (java.util.concurrent.Future) requires that you lot access the effect via a blocking acquire method.Although you lot tin sack telephone telephone isDone() method to detect out if a Java Future has completed earlier calling get, thereby avoiding whatsoever blocking, you lot must hold off until the Java Future has completed earlier proceeding with whatsoever computation that uses the result. With scala.concurrent.Future you lot tin sack attach callbacks for completion (success/failure) or but map it in addition to chain multiple Futures together inwards a monadic fashion without blocking.

What is Companion Object inwards Scala?
If an object has the same advert that a class, the object is called a companion object. H5N1 companion object has access to methods of somebody visibility of the class, in addition to the shape also has access to somebody methods of the object. Doing the comparing with Java, companion objects agree the "static methods" of a class. Just recall that the companion object has to live defined inwards the same origin file that the class. You should also know that Scala classes cannot take away hold static variables or methods. We commonly exercise Companion Objects for Factories.

What is tail recursion inwards Scala? What is the benefit?

H5N1 business office is called tail recursive if the recursive telephone telephone is the lastly functioning inwards the function; the method does non rely on the effect of the recursive telephone telephone for whatsoever to a greater extent than computation. The most of import do goodness of the tail recursive business office is that compiler tin sack rewrite the method inwards an iterative fashion, similar to a patch loop with mutable state. This allows long, deep recursion without taking likewise much of stack retentiveness that could effect inwards StackOverFlowError. Unfortunately, Java compiler doesn't back upwards tail telephone telephone optimization but Scala compiler does. In Scala, you lot tin sack annotate a business office with @tailrec to inform the compiler that this item method is tail recursive. If the compiler cannot laid the business office tail recursive, it volition throw an error.

What is "traits" inwards Scala?

Traits are basically Scala's workaround for the JVM non supporting multiple shape inheritance.  Here is an illustration of traits inwards Scala:

trait Car {   val brand: String }  trait Costly{   val cost: Int  }  trait Milege{   val milege: Int }  class Audi extends Car with Shiny with Miles{   val laid = "Audi"   val cost = 140000   val milege = 20 }

What is Akka, Play, in addition to Sleek inwards Scala?
Akka is a concurrency framework inwards Scala which uses Actor based model for edifice highly concurrent, distributed, in addition to resilient message-driven applications on the JVM. It uses high-level abstractions similar Actor, Future, in addition to Stream to simplify coding for concurrent applications. It also provides charge balancing, routing, partitioning, in addition to adaptive cluster management. If you lot are interested inwards learning Akka, I propose reading Akka inwards Action in addition to Akka documentation, both are dandy resources to acquire Akka.

Play is about other Scala framework to build spider web applications inwards both Java in addition to Scala. The PlayFramework is based on a lightweight, stateless, web-friendly architecture. It is built on Akka, Play provides predictable in addition to minimal resources consumption (CPU, memory, threads) for highly-scalable applications.

Slick is a modern database query in addition to access library for Scala. It allows you lot to piece of work with stored information almost every bit if you lot were using Scala collections patch at the same fourth dimension giving you lot total command over when a database access happens in addition to which information is transferred. You tin sack write your database queries inwards Scala instead of SQL, thence profiting from the static checking, compile-time safety, in addition to compositionality of Scala. Slick features an extensible query compiler which tin sack generate code for dissimilar backends.


What is Spark?
Apache Spark is the large information in addition to cloud computing framework written inwards Scala. The Spark has been engineered from the bottom-up for performance, Spark tin sack live 100x faster than Hadoop for large scale information processing past times exploiting inwards retentiveness computing in addition to other optimizations. Spark is also fast when information is stored on disk, in addition to currently, holds the globe tape for large-scale on-disk sorting. Many developers are at nowadays learning Scala for Spark to acquire into lucrative Big Data Job Market.  I recommend reading "Advanced Analytics with Spark: Patterns for Learning from Data at Scale" past times Sandy Ryza,  Uri Laserson, Sean Owen, in addition to Josh Wills. This mass volition also learn you lot how you lot tin sack exercise functional programming techniques to solve real-world problems, which is a dandy science to have.

What is 'Option' in addition to how is it used inwards Scala?
The 'Option' inwards Scala is similar to Optional of Java 8. It is a wrapper type that avoids the occurrence of a NullPointerException inwards your code past times giving you lot default value inwards instance object is null. When you lot call get() from Option it tin sack render a default value if the value is null. More importantly, Option provides the mightiness to differentiate inside the type organization those values that tin sack live nulled in addition to those that cannot live nulled.

What is ‘Unit’ in addition to ‘()’ inwards Scala?
The 'Unit' is a type similar to void inwards Java. You tin sack say it is a Scala equivalent of the void inwards Java, patch yet providing the linguistic communication with an abstraction over the Java platform. The empty tuple '()' is a term representing a Unit value inwards Scala.

How to compile in addition to run a Scala program?

You tin sack exercise Scala compiler scalac to compile Scala computer program (similar to javac) and scala command to run them (similar to scala)

How to tell Scala to appear into a shape file for about Java class?

Similar to Java, you lot tin sack exercise -classpath declaration to include a JAR inwards Scala's classpath, every bit shown below

$ scala -classpath jar

Alternatively, you lot tin sack also exercise CLASSPATH surroundings variable.


What is the departure betwixt a normal shape in addition to a instance shape inwards Scala?
Following are about key differences betwixt a instance shape in addition to a normal shape inwards Scala:
- instance shape allows pattern matching on it.
- you lot tin sack create instances of instance shape without using the new keyword
- equals(), hashcode() in addition to toString() method are automatically generated for instance classes inwards Scala
- Scala automatically generate accessor methods for all constructor argument

What is the departure inwards betwixt Scala in addition to Java package?

Unlike Java, Scala also supports relative bundle names.


What is the departure betwixt 'concurrency' in addition to 'parallelism'? Name about constructs you lot tin sack exercise inwards Scala to leverage both.
Concurrency is when several computations are executing sequentially during overlapping fourth dimension periods, patch parallelism describes processes that are executed simultaneously. The concepts are often confused because actors tin sack live concurrent in addition to parallel, sometimes simultaneously. For example, Node.js has concurrency via its trial loop despite beingness a unmarried threaded implementation. Parallel collections are a canonical illustration of parallelism, but Futures in addition to the Async library tin sack live every bit well. In short, Concurrency is close avoiding access to mutable the world past times multiple threads at the same time. Parallelism is taking a unmarried task in addition to breaking it apart to live performed past times multiple threads at the same time.


What are 2 ways to laid an executable Scala program?
There are 2 full general strategies: you lot tin sack write a script file in addition to exercise the interpreter, or you lot tin sack compile an object that has a principal method.

What does it hateful that Scala is compatible with Java?

The criterion Scala backend is a Java Virtual Machine. Scala classes are Java classes in addition to vice versa. You tin sack telephone telephone the methods of either linguistic communication from methods inwards the other one. You tin sack extend Java classes inwards Scala, in addition to vice versa. The principal limitation is that about Scala features do non take away hold equivalents inwards Java, for example, traits.

Scala Functional Programming Interview Questions

What is Monad inwards Scala?

H5N1 monad is an object that wraps about other object inwards Scala. It helps to perform the information manipulation of the underlying object, instead of manipulating the object directly.


What are High Order Functions inwards Scala?
High gild functions are functions that tin sack have or render other functions. Common examples inwards Scala are the filter, map,  and flatMap functions, which have other functions every bit arguments.

What is a Closure inwards Scala?

H5N1 closure is also known every bit an anonymous business office whose render value depends upon the value of the variables declared exterior the function.

What is currying inwards Scala?

Currying is a technique to transform a business office that takes multiple arguments into a business office that takes a unmarried argument. There is about characteristic which is inspired past times other business office programming languages similar Haskell in addition to lisp. If you lot desire to acquire to a greater extent than close functional programming techniques inwards Scala, I propose you lot reading Paul Chiusano and Rúnar Bjarnason's Functional Programming inwards Scala 1st edition. It is 1 of the best books to acquire Functional Programming regardless of language. This mass teaches you lot both Scala in addition to Functional Programming through examples in addition to exercise where you lot exercise key features of Scala past times yourself.

That's all close about of the frequently asked Scala interview questions in addition to answers. If you lot are going for a Job interview which requires you lot to piece of work on both Java in addition to Scala so these questions tin sack for sure attention you lot to acquire familiar with key concepts. Though, they barely impact the surface of what Scala offers in addition to what you lot tin sack do with functional programming. This is best for a junior Scala developer with a brace of years sense inwards Scala but for an experienced Scala programmer, a lot to a greater extent than is expected.

If you lot are novel to Scala or desire to acquire Scala from scratch, I recommend reading Martin Odersky's Programming inwards Scala tertiary edition, which is updated for Scala 2.12 version. Martin is the writer of Scala language, so you lot volition non just acquire how to exercise a sure characteristic inwards Scala but the motivation in addition to concept behind it every bit well.

Further Learning
Scala: Getting Started
Learn By Example: Scala
Rock the JVM! Scala in addition to Functional Programming for Beginners

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