High 30 Scala and Practical Programming Interview Questions and Solutions

Whats up guys, in case you are getting ready for Scala Developer interview and searching for ceaselessly requested Scala questions for apply then you’ve gotten come to the correct place. Earlier, I’ve shared finest Scala programs, Scala books, and finest Scala Frameworks and on this article, I’m going to share 30 Scala Questions from previous interviews. Scala is a programming language which goals to supply better of each object-oriented programming and practical programming world. It not solely means that you can  assemble elegant class hierarchies for max code reuse and extensibility but in addition means that you can implement their conduct utilizing higher-order features and different practical programming method. It’s touted as one of many languages which might most likely take over Java, although it did not occur particularly after Java 8 launch which additionally supplies some practical programming instruments to Java e.g. lambda expression and stream. 

However, Scala is an efficient language and created by following finest practices from a number of different programming languages together with Java. Scala is an acronym for “Scalable Language”. This implies it’s designed by holding scalability in thoughts. Many firms e.g. Twitter, LinkedIn, and Intel makes use of it for his or her mission-critical utility.

One of many key energy of Scala is its concise syntax and fewer ceremony i.e. it’s method much less verbose than Java. You possibly can write much less and do extra as a result of the Scala compiler is doing loads of give you the results you want and that is why many builders additionally use Scala as a scripting language. Although, for some, it means Scala is much less readable than Java. You possibly can’t make everybody joyful.

One other beauty of Scala is that it provides a pleasant mixture of object-oriented and practical programming ideas. The language help class and each worth is an object and each operation is a technique name.  Many frequent object oriented design patterns in different languages have built-in help for Scala. For instance, Singleton sample is supported via object definitions and Customer sample is supported via sample matching.

Alternatively, Scala can also be a full-blown practical language. It has every part you’ll count on from a practical programming language like Haskel or Lisp e.g. first-class features, a library with environment friendly immutable information buildings, and a common choice of immutability over mutation.

Yet one more beauty of Scala is that it make full use of mature Java assets, it means that you can use Java libraries in Scala challenge. Scala code is compiled right into a bytecode which might be understood by JVM and by utilizing implicit lessons, Scala even means that you can add new operations to present lessons, regardless of whether or not they come from Scala or Java.

With the trade adoption of Apache Spark, a number one Scala framework for cloud computing and Massive Information, Scala has shortly change into fashionable amongst Massive Information professionals. In case you are going for an interview for any of the Massive Information job openings that require Apache Spark expertise then it’s best to put together for Scala interview questions as properly as a result of Spark is written in Scala.

On this article, I’m going to share some basic Scala language and Practical Programming questions that are helpful for each Java and Massive Information professionals, each newcomers and skilled programmers. 

There may be additionally demand for Scala builders on startups as Scala programmers are only a few as in comparison with Java professionals and they’re additionally thought-about finest programmers, due to the tough studying curve of Scala. They’re additionally fetching superb salaries, someplace within the vary of $100K to $120K, relying in your talent and expertise.

20 Scala Interview Questions and Solutions for Skilled Java Programmers

Right here is my listing of some 20 odd questions from Scala programming and language typically. These are collected from varied sources together with associates and colleagues. It’s largely for Java builders who’re studying Scala or have some expertise working in Scala, searching for a improvement job in Scala. For the reason that demand of Scala builders is on the rise, with a choice for knowledgeable Java programmers, you possibly can use this listing to arrange for telephonic and screening rounds of interviews.

1. What’s the newest model of Scala?
This can be a easy query to examine whether or not you retain your self up-to-date with the most recent details about Scala or not. In case you have not been utilizing Scala actively and do not know the reply then you may say that you’ve got used a sure Scala model. Although, the present model of Scala is Scala 3.2.1, which additionally requires Java 8. Older Scala variations are appropriate with Java 6 and above.

2. Who’s the writer of Scala Programming language?
That is one other primary query about Scala to examine your common information about Scala. It’s designed by Martin Oderskey, a German pc scientist. He additionally teaches a course, Practical Programming Ideas in Scala and Practical Program Design in Scala on Coursera.

3. What’s the distinction between val and var in Scala?

The val key phrase stands for worth and var stands for variable. You should use key phrase val to retailer values, these are immutable, and can’t change as soon as assigned. Alternatively, key phrase var is used to create variables, that are values that may change after being set. Should you attempt to modify a val, the compiler will throw an error. It’s just like the closing variable in Java or const in C++.

4. What’s the distinction between == in Java and Scala?

Scala has extra intuitive notion of equality. The == operator will routinely run the occasion’s equals methodology, somewhat than doing Java type comparability to examine that two objects are literally the identical reference. By the best way, you may nonetheless examine for referential equality by utilizing eq methodology. Briefly, Java == operator examine references whereas Scala calls the equals() methodology. You can even learn the distinction between == and equals() in Java to be taught extra about how they behave in Java, right here.

5. Easy methods to you create Singleton lessons in Scala?

Scala introduces a brand new object key phrase, which is used to characterize Singleton lessons. These are the category with only one occasion and their methodology might be regarded as just like Java’s static strategies. Here’s a Singleton class in Scala:

package deal take a look at

object Singleton{
  def sum(l: Listing[Int]): Int = l.sum
}

This sum methodology is accessible globally, and might be referred to, or imported, because the take a look at.Singleton.sum. A singleton object in Scala also can lengthen lessons and traits.

6. Which books you’ve gotten learn on Scala to date?
This can be a common query to examine how did you be taught Scala, did you learn a e-book or documentation or tutorial and many others. It is best to call the e-book you’ve gotten learn on Scala e.g. I’ve learn Programming in Scala by Martin Odersky and Practical Programming in Scala 1st Version by Paul Chiusano. 

A very powerful factor is, to be sincere, do not identify a e-book you probably have not learn it but. On a special be aware, attempt studying e-book on Scala, Martin Odersky’s Programming in Scala: Up to date for Scala 2.12 is an efficient place to begin.

7. Which key phrase is used to outline a perform in Scala?

A perform is outlined in Scala utilizing the def key phrase. This may occasionally sound acquainted to Python builders as Python additionally makes use of def to outline a perform.

8. What’s using App class in Scala?

Scala supplies a helper class, referred to as App, that gives the primary methodology. As a substitute of writing your personal primary methodology, lessons can lengthen App class to provide concise and executable purposes in Scala as proven within the following instance:

object Primary extends App {
  Console.println("Whats up Scala: " + (args aString ", "))
}

Right here, object Primary inherits the principle methodology of App trait and args returns the present command-line arguments as an array, just like String[] args in Java primary methodology.

9. What is the distinction between the next phrases and kinds in Scala: ‘Nil’, ‘Null’, ‘None’, and ‘Nothing’ in Scala?
Reply: Despite the fact that they give the impression of being comparable, there are some refined variations between them, let’s examine them one after the other:

• Nil represents the top of a Listing.
• Null denotes the absence of worth however in Scala, extra exactly, Null is a kind that represents the absence of kind info for advanced varieties which are inherited from AnyRef. It’s completely different than null in Java. 
• None is the worth of an Possibility if it has no worth in it.
• Nothing is the underside kind of all the Scala kind system, incorporating all sorts below AnyVal and AnyRef. Nothing is often used as a return kind from a way that doesn’t terminate usually and throws an exception

10. What’s the distinction between an object and a category in Scala?
An object is a singleton occasion of a category. It doesn’t must be instantiated by the developer. If an object has the identical identify {that a} class, the item is named a companion object.

11. What’s the distinction between a trait and an summary class in Scala?
Listed here are some key variations between a trait and an summary class in Scala:

• A category can inherit from a number of traits however just one summary class.
• Summary lessons can have constructor parameters in addition to kind parameters. Traits can have solely kind parameters. For instance, you may’t say trait t(i: Int) {}; the i parameter is unlawful.
• Summary lessons are absolutely interoperable with Java. You possibly can name them from Java code with none wrappers. Alternatively, Traits are absolutely interoperable provided that they don’t include any implementation code. See right here to be taught extra about Summary class in Java and OOP. 

12. What’s the distinction between a call-by-value and call-by-name parameter?
The principle distinction between a call-by-value and a call-by-name parameter is that the previous is computed earlier than calling the perform, and the latter is evaluated when accessed.

13. What’s the case class in Scala?

A case class is a particular class definition, which works identical to an everyday Scala class however the compiler creates equals() and toString() strategies, in addition to immutable entry to the sector of the category. You possibly can assemble a case class occasion with out utilizing the new key phrase.

Yet one more advantage of the case lessons is that situations might be decomposed into their constructed fields and can be utilized in sample matching. Right here is an instance of case class hierarchy in Scala, which consists of an summary superclass Car and two concrete case lessons Automobile and Bike

summary class Car
case class Automobile(model: String) extends Car
case class Bike(model: String, value: lengthy) extends Car

Instantiating a case class is straightforward since you don’t want to make use of the brand new key phrase

val myCar = Automobile("BMW")

The constructor parameters of case lessons are handled as public values and might be accessed immediately e.g. myCar.model offers you “BMW”.

Right here is one other instance of traits in Scala utilizing case lessons:

14. What’s the distinction between a Java methodology and a Scala perform?

Scala perform might be handled as a price. It may be assigned to a val or var, and even returned from one other perform, which isn’t attainable in Java. Although Java 8 brings lambda expression which additionally makes perform as a first-class object, which suggests you may cross a perform to a way identical to you cross an object as an argument. See right here to be taught extra concerning the distinction between Scala and Java.

15. What’s the distinction between a Java future and a Scala future?
Despite the fact that each Java and Scala’s Future object supplies asynchronous computation, however there’s a refined distinction between them on the way you retrieve the results of the computation. Java’s Future (java.util.concurrent.Future) requires that you just entry the consequence through a blocking get methodology. 

With scala.concurrent.Future you may connect callbacks for completion (success/failure) or just map it and chain a number of Futures collectively in a monadic vogue with out blocking.
16. What’s Companion Object in Scala?
If an object has the identical identify {that a} class, the item is named a companion object. A companion object has entry to strategies of personal visibility of the category, and the category additionally has entry to personal strategies of the item. Doing the comparability with Java, companion objects maintain the “static strategies” of a category. Simply do not forget that the companion object needs to be outlined in the identical supply file that the category. You must also know that Scala lessons can’t have static variables or strategies. We generally use Companion Objects for Factories.

17. What’s tail recursion in Scala? What’s the profit?

A perform is named tail recursive if the recursive name is the final operation within the perform; the tactic doesn’t depend on the results of the recursive name for any extra computation. A very powerful advantage of the tail recursive perform is that compiler can rewrite the tactic in an iterative vogue, just like some time loop with mutable state. This enables lengthy, deep recursion with out taking an excessive amount of of stack reminiscence that might lead to StackOverFlowError. 

Sadly, Java compiler does not help tail name optimization however Scala compiler does. In Scala, you may annotate a perform with @tailrec to tell the compiler that this specific methodology is tail recursive. If the compiler can’t make the perform tail recursive, it would throw an error.

18. What’s “traits” in Scala?

Traits are principally Scala’s workaround for the JVM not supporting a number of class inheritance.  Right here is an instance of traits in Scala:

trait Automobile {
  val model: String
}

trait Pricey{
  val value: Int 
}

trait Milege{
  val milege: Int
}

class Audi extends Automobile with Shiny with Miles{
  val model = "Audi"
  val value = 140000
  val milege = 20
}

19. What’s Akka, Play, and Glossy in Scala?
Akka is a concurrency framework in Scala which makes use of Actor based mostly mannequin for constructing extremely concurrent, distributed, and resilient message-driven purposes on the JVM. It makes use of high-level abstractions like Actor, Future, and Stream to simplify coding for concurrent purposes. 

It additionally supplies load balancing, routing, partitioning, and adaptive cluster administration. In case you are concerned with studying Akka, I recommend studying Akka in Motion and Akka documentation, each are nice assets to be taught Akka.

Play is one other Scala framework to construct internet purposes in each Java and Scala. The PlayFramework is predicated on a light-weight, stateless, web-friendly structure. It’s constructed on Akka, Play supplies predictable and minimal useful resource consumption (CPU, reminiscence, threads) for highly-scalable purposes.

Slick is a contemporary database question and entry library for Scala. It means that you can work with saved information virtually as for those who had been utilizing Scala collections whereas on the identical time providing you with full management over when a database entry occurs and which information is transferred. 

You possibly can write your database queries in Scala as an alternative of SQL, thus cashing in on the static checking, compile-time security, and compositionality of Scala. Slick options an extensible question compiler which might generate code for various backends. I’ve shared 10 finest Scala frameworks for improvement right here, you too can examine to get extra concepts.

20. What’s Spark?
Apache Spark is the large information and cloud computing framework written in Scala. The Spark has been engineered from the bottom-up for efficiency, Spark might be 100x quicker than Hadoop for large-scale information processing by exploiting in-memory computing and different optimizations. 

I like to recommend becoming a member of these on-line Spark Programs and studying “Superior Analytics with Spark: Patterns for Studying from Information at Scale” by Sandy Ryza,  Uri Laserson, Sean Owen, and Josh Wills. This e-book may even train you ways you need to use practical programming methods to unravel real-world issues, which is a good talent to have.

21. What’s ‘Possibility’ and the way is it utilized in Scala?
The ‘Possibility’ in Scala is just like Non-compulsory of Java 8. It’s a wrapper kind that avoids the incidence of a NullPointerException in your code by providing you with a default worth in case the item is null. While you name get() from Possibility it may return a default worth if the worth is null. Extra importantly, Possibility supplies the flexibility to distinguish inside the kind system these values that may be nulled and people that can’t be nulled.

22. What’s ‘Unit’ and ‘()’ in Scala?
The ‘Unit’ is a kind just like void in Java. You possibly can say it’s a Scala equal of the void in Java, whereas nonetheless offering the language with abstraction over the Java platform. The empty tuple ‘()’ is a time period representing a Unit worth in Scala.

23. Easy methods to compile and run a Scala program?

You should use Scala compiler scalac to compile Scala program (just like javac) and scala command to run them (just like scala)

24. Easy methods to inform Scala to look into a category file for some Java class?

Just like Java, you need to use -classpath argument to incorporate a JAR in Scala’s classpath, as proven under

$ scala -classpath jar

Alternatively, you too can use the CLASSPATH surroundings variable.

25. What’s the distinction between a traditional class and a case class in Scala?
Following are some key variations between a case class and a traditional class in Scala:
– case class permits sample matching on it.
– you may create situations of case class with out utilizing the new key phrase
– equals(), hashcode() and toString() methodology are routinely generated for case lessons in Scala
– Scala routinely generate accessor strategies for all constructor argument

26. What’s the distinction between Scala and Java packages?

Not like Java, Scala additionally helps relative package deal names.

27. What’s the distinction between ‘concurrency’ and ‘parallelism’? Title some constructs you need to use in Scala to leverage each.
Concurrency is when a number of computations are executing sequentially throughout overlapping time intervals, whereas parallelism describes processes which are executed concurrently. The ideas are sometimes confused as a result of actors might be concurrent and parallel, generally concurrently. For instance, Node.js has concurrency through its occasion loop regardless of being a single-threaded implementation. Parallel collections are a canonical instance of parallelism, however Futures and the Async library might be as properly. Briefly, Concurrency is about avoiding entry to mutable states by a number of threads on the identical time. Parallelism is taking a single process and breaking it aside to be carried out by a number of threads on the identical time.

28. What are two methods to make an executable Scala program?
There are two common methods: you may write a script file and use the interpreter, or you may compile an object that has a primary methodology.

29. What does it imply that Scala is appropriate with Java?

The usual Scala backend is a Java Digital Machine. Scala lessons are Java lessons and vice versa. You possibly can name the strategies of both language from strategies within the different one. You possibly can lengthen Java lessons in Scala, and vice versa. The principle limitation is that some Scala options would not have equivalents in Java, for instance, traits.

Scala Practical Programming Interview Questions

30. What’s Monad in Scala?

A monad is an object that wraps one other object in Scala. It helps to carry out the info manipulation of the underlying object, as an alternative of manipulating the item immediately.

31. What are Excessive Order Features in Scala?
Excessive order features are features that may obtain or return different features. Widespread examples in Scala are the filter, map,  and flatMap features, which obtain different features as arguments.

32. What’s a Closure in Scala?

A closure is also called an nameless perform whose return worth relies upon upon the worth of the variables declared outdoors the perform.

33. What’s currying in Scala?

Currying is a way to rework a perform that takes a number of arguments right into a perform that takes a single argument. There may be some characteristic which is impressed by different practical programming languages like Haskell and lisp. 

If you wish to be taught extra about practical programming methods in Scala, I recommend you learn Paul Chiusano and Rúnar Bjarnason’s Practical Programming in Scala 1st version. It is among the finest books to be taught Practical Programming no matter language. This e-book teaches you each Scala and Practical Programming via examples and workouts the place you utilize key options of Scala by your self.

That is all about a few of the ceaselessly requested Scala interview questions and solutions. In case you are going for a Job interview that requires you to work on each Java and Scala then these questions can definitely provide help to to get conversant in key ideas. 

Although, they barely contact the floor of what Scala provides and what you are able to do with practical programming. That is finest for a junior Scala developer with a few years of expertise in Scala however for an skilled Scala programmer, much more is predicted.

In case you are new to Scala or need to be taught Scala from scratch, I like to recommend becoming a member of these on-line Scala Programming programs and studying Martin Odersky’s Programming in Scala third version, which is up to date for Scala 2.12 model. Martin is the writer of Scala language, so you’ll not simply discover ways to use a sure characteristic in Scala however the motivation and idea behind it as properly.

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