Top Thirty Scala Together With Functional Programming Interview Questions Together With Answers

Scala is a programming linguistic communication which aims to supply best of both object-oriented programming together with functional programming world. It non alone allows y'all to  build elegant course of report hierarchies for maximum code reuse together with extensibility but also allows y'all to implement their conduct using higher-order functions together with other functional programming technique. It is touted every bit i of the languages which tin belike take away hold over Java, though it didn't travel on peculiarly after Java 8 unloose which also provides around functional programming tools to Java e.g. lambda expression together with stream. Nevertheless, Scala is a proficient linguistic communication together with created past times next best practices from several other programming languages including Java. Scala is an acronym for “Scalable Language”. This way it is designed past times keeping scalability inwards mind. Many companies e.g. Twitter, LinkedIn, together with Intel uses it for their mission-critical application.

One of the key forcefulness of Scala is its concise syntax together with less ceremony i.e. it is way less verbose than Java. You tin write less together with do to a greater extent than because the Scala compiler is doing a lot of piece of work for y'all together with that's why many developers also utilisation Scala every bit a scripting language. Though, for some, it way Scala is less readable than Java. You can't fix everyone happy.

Another neat thing well-nigh Scala is that it offers a prissy mix of object-oriented together with functional programming concepts. The linguistic communication back upward course of report together with every value is an object together with every functioning is a method call.  Many mutual object oriented blueprint patterns inwards other languages take away hold built-in back upward for Scala. For example, Singleton pattern is supported through object definitions together with Visitor pattern is supported through pattern matching.


On the other hand, Scala is also a full-blown functional language. It has everything y'all would await from a functional programming linguistic communication similar Haskel or Lisp e.g. excellent functions, a library with efficient immutable information structures, together with a full general preference of immutability over mutation.

One to a greater extent than neat thing well-nigh Scala is that it fix total utilisation of mature Java resources, it allows y'all to utilisation Java libraries inwards Scala project. Scala code is compiled into a bytecode which tin live understood past times JVM together with past times using implicit classes, Scala fifty-fifty allows y'all to add together novel operations to existing classes, no thing whether they come upward from Scala or Java.

With the manufacture adoption of Apache Spark, a leading Scala framework for cloud computing together with Big Data, Scala has apace conk pop with Big Data professionals. If y'all are going for an interview for whatsoever of the Big Data task openings that require Apache Spark sense together with so y'all should fix for Scala interview questions every bit good because Spark is written inwards Scala.

In this article, I am going to portion around key Scala linguistic communication together with Functional Programming questions which are useful for both Java together with Big Data professional, both newcomers together with experienced programmers. There is also a proficient demand for Scala developers on startups every bit Scala programmers are rattling less every bit compared to Java professionals together with they are also considered best programmers, cheers to the hard learning curvature of Scala. They are also fetching rattling proficient salaries, somewhere inwards the attain of $100K to $120K, depending on your science together with experience.

Scala Interview Questions together with Answers

Here is my listing of around xx strange questions from Scala programming together with linguistic communication inwards general. These are collected from diverse sources including friends together with colleagues. It is generally for Java developers who are learning Scala or take away hold around sense working inwards Scala, looking for evolution task inwards Scala. Since the demand of Scala developer is on the rise, with preference to experienced Java programmers, y'all could utilisation this listing to fix for telephonic together with screening circular of interviews.


What is the latest version of Scala?
This is a uncomplicated interrogation to banking enterprise check whether y'all maintain yourself up-to-date with the latest information well-nigh Scala or not. If y'all take away hold non been using Scala actively together with don't know the reply together with so y'all tin say that y'all take away hold used sure Scala version. Though, the electrical current version of Scala is Scala 2.12, which also require Java 8. Older Scala versions are compatible with Java six together with above.


Who is the writer of Scala Programming language?
This is around other basic interrogation well-nigh Scala to banking enterprise check your full general cognition well-nigh Scala. It is designed past times Martin Oderskey, a High German estimator scientist. He also teaches a course, Functional Programming Principles inwards Scala together with Functional Program Design inwards Scala on Coursera.

What is the deviation betwixt val together with var inwards Scala?

The val keyword stands for value together with var stands for variable. You tin utilisation keyword val to shop values, these are immutable, together with cannot alter i time assigned. On the other hand, keyword var is used to create variables, which are values that tin alter after beingness set. If y'all attempt 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 deviation betwixt == inwards Java together with 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 trend comparing to banking enterprise check that 2 objects are genuinely the same reference. By the way, y'all tin all the same banking enterprise check for referential equality past times using eq method. In short, Java == operator compare references spell Scala calls the equals() method. You tin also read the deviation betwixt == together with equals() inwards Java to larn to a greater extent than well-nigh how they acquit inwards Java, here.

How to y'all create Singleton classes inwards Scala?

Scala introduces a novel object keyword, which is used to stand upward for Singleton classes. These are the course of report with just i instance together with their method tin live idea of every bit similar to Java's static methods. Here is a Singleton course of report inwards Scala:

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

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


Which books y'all take away hold read on Scala so far?
This is a full general interrogation to banking enterprise check how did y'all larn Scala, did y'all read mass or documentation or tutorial etc. It's best to mention the mass y'all take away hold read on Scala e.g. I take away hold read Programming inwards Scala by Martin Odersky together with Functional Programming inwards Scala 1st Edition past times Paul Chiusano. If y'all take away hold non read whatsoever mass together with so just say y'all take away hold non read whatsoever mass yet together with similar to read Scala documentation or planning to read a mass etc. The most of import thing is, to live honest, don't mention a mass if y'all take away hold non read it yet. On a dissimilar note, attempt reading a proficient mass on Scala, Martin Odersky's Programming inwards Scala: Updated for Scala 2.12 is a proficient starting point.

Which keyword is used to define a constituent inwards Scala?

H5N1 constituent 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 utilisation of App course of report inwards Scala?

Scala provides a helper class, called App, that provides the main method. Instead of writing your ain top dog method, classes tin extend App course of report to create concise together with 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 top dog method of App trait together with args returns the electrical current command occupation arguments every bit an array, similar to String[] args inwards Java top dog method.


What's the deviation betwixt the next terms together with types inwards Scala: 'Nil', 'Null', 'None', together with 'Nothing' inwards Scala?
Answer: Even though they seem similar, at that spot are around subtle differences betwixt them, let's come across them i past times one:

• Nil represents the halt 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 together with AnyRef. Nothing is commonly used every bit a render type from a method that does non terminate usually together with throws an exception

What is the deviation betwixt an object together with a course of report 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 mention that a class, the object is called a companion object.


What is the deviation betwixt a trait together with an abstract course of report inwards Scala?
Here are around key differences betwixt a trait together with an abstract course of report inwards Scala:

• A course of report tin inherit from multiple traits but alone i abstract class.
• Abstract classes tin take away hold constructor parameters every bit good every bit type parameters. Traits tin take away hold alone type parameters. For example, y'all can’t say trait t(i: Int) {}; the i parameter is illegal.
• Abstract classes are fully interoperable with Java. You tin telephone phone them from Java code without whatsoever wrappers. On the other hand, Traits are fully interoperable alone if they do non incorporate whatsoever implementation code. See hither to larn to a greater extent than well-nigh Abstract class inwards Java together with OOP. 

What is the deviation betwixt a call-by-value together with call-by-name parameter?
The top dog deviation betwixt a call-by-value and a call-by-name parameter is that the one-time is computed earlier calling the function, together with the subsequently is evaluated when accessed.

What is the instance course of report inwards Scala?

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

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

Instantiating a instance course of report is slowly because y'all don’t demand to utilisation the novel keyword

val myCar = Car("BMW")

The constructor parameters of instance classes are treated every bit public values together with tin live accessed direct e.g. myCar.brand volition give y'all "BMW".

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

What is the deviation betwixt a Java method together with a Scala function?

Scala constituent tin live treated every bit a value. It tin live assigned to a val or var, or fifty-fifty returned from around other function, which is non possible inwards Java. Though Java 8 brings lambda seem which also makes constituent every bit a starting fourth dimension course of report object, which way y'all tin travel past times a constituent to a method just similar y'all travel past times an object every bit an argument. See here to larn to a greater extent than well-nigh the deviation betwixt Scala together with Java.


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

What is Companion Object inwards Scala?
If an object has the same mention that a class, the object is called a companion object. H5N1 companion object has access to methods of somebody visibility of the class, together with the course of report also has access to somebody methods of the object. Doing the comparing with Java, companion objects concur the "static methods" of a class. Just recall that the companion object has to live defined inwards the same beginning file that the class. You should also know that Scala classes cannot take away hold static variables or methods. We commonly utilisation Companion Objects for Factories.

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

H5N1 constituent is called tail recursive if the recursive telephone phone is the lastly functioning inwards the function; the method does non rely on the consequence of the recursive telephone phone for whatsoever to a greater extent than computation. The most of import do goodness of the tail recursive constituent is that compiler tin rewrite the method inwards an iterative fashion, similar to a spell loop with mutable state. This allows long, deep recursion without taking also much of stack retentivity that could consequence inwards StackOverFlowError. Unfortunately, Java compiler doesn't back upward tail telephone phone optimization but Scala compiler does. In Scala, y'all tin annotate a constituent with @tailrec to inform the compiler that this detail method is tail recursive. If the compiler cannot fix the constituent tail recursive, it volition throw an error.

What is "traits" inwards Scala?

Traits are basically Scala's workaround for the JVM non supporting multiple course of report 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 fix = "Audi"   val cost = 140000   val milege = 20 }

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

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

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


What is Spark?
Apache Spark is the large information together with cloud computing framework written inwards Scala. The Spark has been engineered from the bottom-up for performance, Spark tin live 100x faster than Hadoop for large scale information processing past times exploiting inwards retentivity computing together with other optimizations. Spark is also fast when information is stored on disk, together with 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, together with Josh Wills. This mass volition also learn y'all how y'all tin utilisation functional programming techniques to solve real-world problems, which is a neat science to have.

What is 'Option' together with 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 y'all default value inwards instance object is null. When y'all call get() from Option it tin render a default value if the value is null. More importantly, Option provides the mightiness to differentiate inside the type arrangement those values that tin live nulled together with those that cannot live nulled.

What is ‘Unit’ together with ‘()’ inwards Scala?
The 'Unit' is a type similar to void inwards Java. You tin say it is a Scala equivalent of the void inwards Java, spell all the same 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 together with run a Scala program?

You tin utilisation Scala compiler scalac to compile Scala programme (similar to javac) and scala command to run them (similar to scala)

How to tell Scala to seem into a course of report file for around Java class?

Similar to Java, y'all tin utilisation -classpath declaration to include a JAR inwards Scala's classpath, every bit shown below

$ scala -classpath jar

Alternatively, y'all tin also utilisation CLASSPATH surroundings variable.


What is the deviation betwixt a normal course of report together with a instance course of report inwards Scala?
Following are around key differences betwixt a instance course of report together with a normal course of report inwards Scala:
- instance course of report allows pattern matching on it.
- y'all tin create instances of instance course of report without using the new keyword
- equals(), hashcode() together with toString() method are automatically generated for instance classes inwards Scala
- Scala automatically generate accessor methods for all constructor argument

What is the deviation inwards betwixt Scala together with Java package?

Unlike Java, Scala also supports relative bundle names.


What is the deviation betwixt 'concurrency' together with 'parallelism'? Name around constructs y'all tin utilisation inwards Scala to leverage both.
Concurrency is when several computations are executing sequentially during overlapping fourth dimension periods, spell parallelism describes processes that are executed simultaneously. The concepts are often confused because actors tin live concurrent together with parallel, sometimes simultaneously. For example, Node.js has concurrency via its lawsuit loop despite beingness a unmarried threaded implementation. Parallel collections are a canonical illustration of parallelism, but Futures together with the Async library tin live every bit well. In short, Concurrency is well-nigh avoiding access to mutable land past times multiple threads at the same time. Parallelism is taking a unmarried task together with breaking it apart to live performed past times multiple threads at the same time.


What are 2 ways to fix an executable Scala program?
There are 2 full general strategies: y'all tin write a script file together with utilisation the interpreter, or y'all tin compile an object that has a top dog 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 together with vice versa. You tin telephone phone the methods of either linguistic communication from methods inwards the other one. You tin extend Java classes inwards Scala, together with vice versa. The top dog limitation is that around 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 around 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 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 constituent 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 constituent that takes multiple arguments into a constituent that takes a unmarried argument. There is around characteristic which is inspired past times other constituent programming languages similar Haskell together with lisp. If y'all desire to larn to a greater extent than well-nigh functional programming techniques inwards Scala, I propose y'all reading Paul Chiusano and Rúnar Bjarnason's Functional Programming inwards Scala 1st edition. It is i of the best books to larn Functional Programming regardless of language. This mass teaches y'all both Scala together with Functional Programming through examples together with exercise where y'all utilisation key features of Scala past times yourself.

That's all well-nigh around of the frequently asked Scala interview questions together with answers. If y'all are going for a Job interview which requires y'all to piece of work on both Java together with Scala together with so these questions tin sure enough assistance y'all to acquire familiar with key concepts. Though, they barely impact the surface of what Scala offers together with what y'all tin do with functional programming. This is best for a junior Scala developer with a duo of years sense inwards Scala but for an experienced Scala programmer, a lot to a greater extent than is expected.

If y'all are novel to Scala or desire to larn 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 y'all volition non just larn how to utilisation a sure characteristic inwards Scala but the motivation together with concept behind it every bit well.

Further Learning
Scala: Getting Started
Learn By Example: Scala
Rock the JVM! Scala together with Functional Programming for Beginners

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