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Scala Interview Questions

When choosing a programming language for big data applications, Python and R are the most preferred programming languages ​​among data scientists, and Java is the reference language for developing applications on Hadoop. With the introduction of Scala-based big data frameworks like Apache Kafka and Apache Spark, Scala is becoming increasingly popular with big data professionals. Every developer in the big data world should be smart enough to learn a programming language with a certain level of complexity.

Scala, the unrivaled programming language with its phenomenal capabilities to handle petabytes of big data with ease. Scala is mastering deep-rooted languages ​​like Java and Python. This Scala Interview Questions article will cover the crucial questions that can help you get a job. I have lined up the questions as below.

Why is Scala called a scalable language?

Scala is a general purpose language powered by the JVM. It has some unique features that make it very useful for developing programs of various shapes and sizes. Scala provides developers with a lot of design and implementation flexibility, from small script to enterprise-grade multi-module applications. Type inference, implicit conversion, and its brevity help define custom control structures and domain specific languages. On the one hand, its object-oriented features help to design systems with complex objects. On the other hand, functional programming constructs help you develop error-free and reusable code. In short, the language is suitable for all kinds of requirements. This is why it is called a scalable language.

What is a Scala card?

Scala Map is a collection of key-value pairs for which the value in a map can be retrieved using the key. The values ​​in a scala map are not unique, but the keys are unique. Scala supports two types of cards: mutable and immutable. By default, Scala supports immutable mappings, and to use mutable mapping, programmers must explicitly import the scala.collection.mutable.Map class. When programmers want to use a mutable map and an immutable map together in the same program, the mutable map can be accessed as mutable.map and the immutable map can be accessed by the name of the map.

Which Scala library is used for functional programming?

The Scalaz library has purely functional data structures that complement the standard Scala library. It has a predefined set of basic type classes like Monad, Functor, etc.

What is the difference between flatMap() and map() operations?

FlatMap is a transformation operation in Apache Spark to create an RDD from existing RDD. It takes one element from an RDD and can produce 0, 1 or many outputs based on business logic. It is similar to Map operation, but Map produces one to one output. If we perform Map operation on an RDD of length N, output RDD will also be of length N. But for FlatMap operation output RDD can be of different length based on business logic
val array1d = Array(“Hello,World”, “This,is,an,example”)
//array1d is an array of strings
val maped_array = array1d.map(x => x.split(“,”))
//maped_array will be: Array(Array(Hello, World), Array(This, is, an, example))
val flatMap_array = array1d.flatMap(x => x.split(“,”))
//flatMap_array will be: Array(Hello, World, This, is, an, example)

What do you mean by "unit" and "()" in Scala?

Unit is a subtype of scala.anyval and nothing more than the Scala equivalent of Java void, which Scala provides an abstraction of the Java platform. The empty tuple, i.e. H. () in scala is a term that represents the unit value.

What is the difference between parallelism and parallelism?

The terms parallelism and parallelism are often confused. When multiple calculations are performed sequentially for overlapping periods of time, this is called parallelism, while the simultaneous execution of the processes is called parallelism. The parallel collection, futures library, and async are examples of how parallelism can be achieved in Scala.

Why do we need App in Scala?

App is a helper class that holds the main method and its Members together. The App trait can be used to quickly turn Objects into Executable programs. We can have our classes extend App to render the executable code.
object Edureka extends App{
     println("Hello World")
   }

What is a monad in Scala?

The easiest way to define a monad is to associate it with an envelope. Each class object is wrapped in Scala with a monad. Like wrapping gifts or presents in shiny packaging with ribbons to make them look attractive, Monads in Scala are used for wrapping objects and have two important functions:
  • Identity through "unity" in Scala
  • Link with "flatMap" in Scala

Distinguish between Val and Var in Scala.

Val and var are the two keywords used to define variables in Scala. The Var keyword is similar to declaring variables in Java, while Val is slightly different. After a variable has been declared with Val, the reference cannot be changed to refer to a different reference. This functionality of the Val keyword in Scala can be related to the functionality of the last keyword in Java. For simplicity, Val refers to the immutable declaration of a variable, while var refers to the mutable declaration of a variable in Scala.

What is mean t by closure in Scala?

The closure is a function in Scala where the return value of the function depends on the value of one or more variables that were declared outside the function.

What is the option in Scala? Why would you use it?

It is used to represent whether a value is present or not. Option collections can be used to enclose missing values. It can also be seen as a substitute for returning null values, which can be very helpful in reducing the occurrence of NullPointerException. The option type itself is not implemented, but depends on two subtypes: Some and None.

What is the difference between var, val and def in Scala?

A var is a variable. It’s a mutable reference to a value. Since it’s mutable, its value may change through the program lifetime.

On the other hand, val keyword represents a value. It’s an immutable reference, mean ing that its value never changes. Once assigned it will always keep the same value. It’s similar to a final variable in Java or constants in other languages. It’s also worth to remember that the variable type cannot change in Scala. You may say that a var behaves similarly to Java variables.

While the def is a function declaration. It is evaluated on call, similar to Python, where def is also used to declare a function.

What is a Scala trait?

A trait is a special type of class that allows the use of multiple inheritance. A feature can only extend one class, but a class can have multiple features. However, unlike classes, features cannot be instantiated.
trait Printable{
   def print()
}
class A4 extends Printable{
   def print(){
      println("Hello")
  }
}
object MainObject{
   def main(args:Array[String]){
      var a = new A4()
      a.print()
  }
}

When do you use Scala traits?

Traits are mainly used when we need a dependency injection. Unlike Java, dependency injection through the Spring framework is accomplished through annotations. In Scala there are no annotations or any special packages that need to be imported. We just have to initialize the class with the property and voila, the dependency is injected.

What should be considered when using Scala streams?

Streams in Scala are a kind of lazy collection that is created with the start element and then recursively generated with these elements. Streams are like a list, except items are only added when accessed, so they are "lazy." Also, since streams are lazy to add items, they can be unlimited, and once added they are cached. Because streams can be unlimited and all values ​​are computed at access time, programmers should be careful when using non-transformer methods as this can lead to java.lang.OutOfMemoryErrors.

What do you understand by diamond problems and how does Scala solve them?

The multiple inheritance problem is known as the fatal diamond problem or the diamond problem. The inability to decide which implementation of the method to choose is called the Scala diamond problem. For example, suppose classes B and C inherit from class A, while class D inherits from both classes B and C. Now, while multiple inheritance is implemented when B and C override a method of class A, always there is confusion and a dilemma as to which implementation D should inherit. This is known as the diamond problem. Scala solves the diamond problem using the concept of features and class linearization rules.

What is tail recursion in Scala?

There are several situations in which programmers need to write recursive functions. The main problem with recursive functions is that they can consume all the allocated stack space. To overcome this situation, the Scala compiler provides a "tail recursion" mechanism to optimize these recursive functions so that a new stack location is not created, but the current function stack location is used. To qualify for this, the annotation "@ annotation.tailrec" must be used before the function definition and the recursive call must be the last declaration, otherwise only the function will compile, there will be an error.

What do you understand by implicit parameters?

Whenever we need the function to be able to be called without passing all the parameters, we use implicit parameters. We provide the default values ​​for any parameter or parameter that we want to use implicitly. If the function is called without passing the implicit parameters, the local value of this parameter is used. We need to use the implicit keyword to implicitly make a value, function parameter, or variable.

How does the performance work in Scala?

The yield keyword, when given before the expression, the value returned by each expression, is returned as a collection. The yield keyword is very useful when you want to use the return value of the expression. The returned collection can be used as a normal collection and repeated in another loop.

What is Scala Future? How is it different from java.util.concurrent.Future?

Scala Future is a monadic collection that starts a task in the background. It is an object that has the potential or future worth that would be available after the task was completed. It also offers various operations to further concatenate the operations or to extract the value. Future also offers various callback functions such as onComplete, OnFailure, onSuccess, to name a few, which makes Future a complete concurrent task class. The main difference between Scala’s Future class and Java’s Future class is that the latter does not provide promise / callback operations. The only way to get the result is to use Future.get () in Java.

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