Scala Interview FAQs Archives | Page 3 of 5 | 800+ Java & Big Data Interview Q&As

Blog Archives

« 1 2 3 4 5 »

11: Coding Scala Way – Actors with Akka – part 1

We already saw in Java: Producer and Consumer Java Multi-threading code. This extends the tutorial “Simple Akka tutorial in Scala step by step” for setting up the environment with right plugins and libraries with Eclipse & Maven.

The Akka Actors sending &…

11A: Scala values, proper types, first order types & higher kinded types

Q1. What is a proper type in Scala? A1. String, List[Int], List[String], Person, etc are proper types in Scala. The below diagram will become clearer at the end.


package com.sbthello

object ProperType {
  
  val a: Int = 5
  
  val b: String = "5"
  
  val list1: List[String] = List("1","2","3")
  
  val  list2: List[Int] = List(1 ,2, 3)

  case class Person(name: String, age: Int)
  
  val p: Person = Person("John", 5)
  
  val map: Map[String, Int] = Map("Key1" -> 5, "Key2" -> 8)
  
}

package com.sbthello

object ProperType {

val a: Int = 5

val b: String = "5"

val list1: List[String] = List("1","2","3")

val list2: List[Int] = List(1 ,2, 3)

case class Person(name: String, age: Int)

val p: Person = Person("John", 5)

val map: Map[String, Int] = Map("Key1" -> 5, "Key2" -> 8)

}

Proper types are a higher level concept than values (E.g. … Read more ›...

This content is for 30-Day-Full-Access, 100-Day-Full-Access, 200-Day-Full-Access, and 365-Day-Full-Access members only. Register 80+ Free Java FAQs 80+ Free Big Data FAQs

Already a member? Log in here

11B: Q71 – Q72 – Scala type parameterization & variance interview Q&As

Q71. Does Scala have type erasure as in Java?
A71. Yes. Scala parametrized types loose the type information after compilation in the same way as Java does.

Q72a. What are different type parameter modifiers in Scala?
A72a.

Cage[T]
T is of any type
Invariance

Cage[T <: Animal]
T is sub type of an Animal
upper bound,

…

11C: Q73 – Q77 – Scala type parameterization & variance interview Q&As

This extends the type parameters basics at 11B: Q71 – Q72 – Scala type parameterization & variance interview Q&As. Cage[T] T is of any type Invariance Cage[T <: Animal] T is sub type of an Animal upper bound, … Read more ›...

This content is for 30-Day-Full-Access, 100-Day-Full-Access, 200-Day-Full-Access, and 365-Day-Full-Access members only. Register 80+ Free Java FAQs 80+ Free Big Data FAQs

Already a member? Log in here

11D: Scala existential type interview Q&As

Q01. What are existential types? A01. Existential types are a way of abstracting over types. They let you assert that some type “exists” without specifying exactly what it is as you don’t care what it is in the current context. For example, counting the number of elements in a list....

This content is for 30-Day-Full-Access, 100-Day-Full-Access, 200-Day-Full-Access, and 365-Day-Full-Access members only. Register 80+ Free Java FAQs 80+ Free Big Data FAQs

Already a member? Log in here

12: Coding Scala Way – Actors with Akka “Ask Pattern” – Part 2

Actors with Akka “Ask Pattern” is for getting a reply or a response to a message that was sent by a sender. Use ? or ask method. We saw earlier how to send or tell a message to an actor. The Akka Actor Asking for a reply or response The...

This content is for 30-Day-Full-Access, 100-Day-Full-Access, 200-Day-Full-Access, and 365-Day-Full-Access members only. Register 80+ Free Java FAQs 80+ Free Big Data FAQs

Already a member? Log in here

12: Q78 – Q80 Recursion in Scala Q&As explained with diagrams

Q. Do functional languages handle recursion better than non-functional ones?

A. Yes because they have to. A pure function is a function with no side effects and no state. Not having side effects means you can’t have loop counters as they mutate state,

…

13: Coding Scala Way – 2 Actors with Akka – part 3

This extends Actors with Akka – part 1. This “Akka with actors” shows how messages passed among actors in the system. This is known as the reactor pattern based on the event-driven architecture. Orderplacement.scala with Actors


import akka.actor._;

case class OrderMessage(orderId: String)
case class InvoiceMessage(orderId: String, invoiceId: String)

class OrderingSystem(dispatcher: ActorRef) extends Actor {
  var orderCount = 0;

  def receive = {
    case InvoiceMessage(ordeId, invoiceId) =>
      println("<- Receved invoice " + invoiceId + " for the order " + ordeId)
    case OrderMessage =>
      println("== Placing order")
      orderCount += 1
      dispatcher ! OrderMessage("ORDER-" + orderCount)
  }
}

class DispatchSystem extends Actor {
  var invoiceCount = 0;

  def receive = {
    case OrderMessage(ordeId) =>
      println("-> Receved order " + ordeId)
      println("==> Dispatching the order " + ordeId)
      Thread.sleep(3000)
      invoiceCount += 1
      sender ! InvoiceMessage(ordeId, "INV-" + invoiceCount)
    case _ =>
  }
}

object OrderPlacementSystem extends App {

  val system = ActorSystem("OrderPlacement")
  val dispatcher = system.actorOf(Props[DispatchSystem], name = "dispatcher")
  val ordering = system.actorOf(Props(new OrderingSystem(dispatcher)), name = "order-placer")

  (1 to 5).map(x => ordering ! OrderMessage) //place 5 orders
}

import akka.actor._;

case class OrderMessage(orderId: String)

case class InvoiceMessage(orderId: String, invoiceId: String)

class OrderingSystem(dispatcher: ActorRef) extends Actor {

var orderCount = 0;

def receive = {

case InvoiceMessage(ordeId, invoiceId) =>

println("<- Receved invoice " + invoiceId + " for the order " + ordeId)

case OrderMessage =>

println("== Placing order")

orderCount += 1

dispatcher ! OrderMessage("ORDER-" + orderCount)

}

class DispatchSystem extends Actor {

var invoiceCount = 0;

def receive = {

case OrderMessage(ordeId) =>

println("-> Receved order " + ordeId)

println("==> Dispatching the order " + ordeId)

Thread.sleep(3000)

invoiceCount += 1

sender ! InvoiceMessage(ordeId, "INV-" + invoiceCount)

case _ =>

}

object OrderPlacementSystem extends App {

val system = ActorSystem("OrderPlacement")

val dispatcher = system.actorOf(Props[DispatchSystem], name = "dispatcher")

val ordering = system.actorOf(Props(new OrderingSystem(dispatcher)), name = "order-placer")

(1 to 5).map(x => ordering ! OrderMessage) //place 5 orders

}

Output:


== Placing order
== Placing order
== Placing order
-> Receved order ORDER-1
==> Dispatching the order ORDER-1
== Placing order
== Placing order
-> Receved order ORDER-2
==> Dispatching the order ORDER-2
<- Receved invoice INV-1 for the order ORDER-1
-> Receved order ORDER-3
<- Receved invoice INV-2 for the order ORDER-2
==> Dispatching the order ORDER-3
-> Receved order ORDER-4
<- Receved invoice INV-3 for the order ORDER-3
==> Dispatching the order ORDER-4
-> Receved order ORDER-5
==> Dispatching the order ORDER-5
<- Receved invoice INV-4 for the order ORDER-4
<- Receved invoice INV-5 for the order ORDER-5

== Placing order

-> Receved order ORDER-1

==> Dispatching the order ORDER-1

== Placing order

-> Receved order ORDER-2

==> Dispatching the order ORDER-2

<- Receved invoice INV-1 for the order ORDER-1

-> Receved order ORDER-3

<- Receved invoice INV-2 for the order ORDER-2

==> Dispatching the order ORDER-3

-> Receved order ORDER-4

<- Receved invoice INV-3 for the order ORDER-3

==> Dispatching the order ORDER-4

-> Receved order ORDER-5

==> Dispatching the order ORDER-5

<- Receved invoice INV-4 for the order ORDER-4

<- Receved invoice INV-5 for the order ORDER-5

The system keeps running until you stop the JVM process. …...

This content is for 30-Day-Full-Access, 100-Day-Full-Access, 200-Day-Full-Access, and 365-Day-Full-Access members only. Register 80+ Free Java FAQs 80+ Free Big Data FAQs

Already a member? Log in here

13A: Scala Semigroup interview Q&As

Semigroups, Monoids, Functors, Monads, Applicatives, etc are concepts or patterns that abstract complexities in computations, and NOT traits or classes. You can think of them as type classes like List[T], Option[T], Futures[T], MyContainer[T], etc that fulfil requirements of functors, monads, etc. Let’s start with monoids first. … Read more ›...

This content is for 30-Day-Full-Access, 100-Day-Full-Access, 200-Day-Full-Access, and 365-Day-Full-Access members only. Register 80+ Free Java FAQs 80+ Free Big Data FAQs

Already a member? Log in here

13B: Q81 – Q83 Scala monoids interview Q&As

Monoids, Functors, Monads, Applicatives, etc are concepts or patterns that abstract complexities in computations, and NOT traits or classes. You can think of them as container type classes like List[T], Option[T], Futures[T], MyContainer[T], etc that fulfil requirements of functors, monads, etc. Let’s start with monoids first. … Read more ›...

This content is for 30-Day-Full-Access, 100-Day-Full-Access, 200-Day-Full-Access, and 365-Day-Full-Access members only. Register 80+ Free Java FAQs 80+ Free Big Data FAQs

Already a member? Log in here

13B: Scala foldLeft, foldRight, scanLeft, scanRight, reduceLeft, reduceRight, etc are Monoids

This extends 13: Q81 – Q83 Scala monoids interview Q&As. Given the below code

package com.myapp

object FoldIsAMonoid extends App {

  val xs: List[Double] = List(1.0,2.0,3.0, 4.0)
  val ys: List[Int] = List(11,22, 33)

  val map1 = Map ("John" -> 22,
    "Peter" -> 33,
    "Sam"-> 97
  )

  val map2 = Map ( "John" -> 7,
    "Peter" -> 9
  )
}

package com.myapp

object FoldIsAMonoid extends App {

val xs: List[Double] = List(1.0,2.0,3.0, 4.0)

val ys: List[Int] = List(11,22, 33)

val map1 = Map ("John" -> 22,

"Peter" -> 33,

"Sam"-> 97

)

val map2 = Map ( "John" -> 7,

"Peter" -> 9

)

}

Q01. How will you combine the two lists xs & xy? A01. The foldLeft(.)(..) to the rescue as shown below:

 override def foldLeft[B](z: B)(op: (B, A) => B): B

1	override def foldLeft[B](z: B)(op: (B, A) => B): B

 val result = ys.foldLeft(xs)((xs_acc,y) => xs_acc.:+(y.asInstanceOf[Double]))
  println(result);

val result = ys.foldLeft(xs)((xs_acc,y) => xs_acc.:+(y.asInstanceOf[Double]))

println(result);

:+ is a method name alias for the append:


final def:+[B >: A](elem: B): List[B]

final def:+[B >: A](elem: B): List[B]

Output:

List(1.0, 2.0, 3.0, 4.0, 11.0, 22.0, 33.0)

1 2	List(1.0, 2.0, 3.0, 4.0, 11.0, 22.0, 33.0)

Q02....

This content is for 30-Day-Full-Access, 100-Day-Full-Access, 200-Day-Full-Access, and 365-Day-Full-Access members only. Register 80+ Free Java FAQs 80+ Free Big Data FAQs

Already a member? Log in here

14: Coding Scala Way – Scala concurrency with Future

Scala concurrency with Future explains step by step blocking vs unblocking calls and how implicit and apply concepts work under the covers. Scala extends the Java programming language and runtime in many ways, including concurrency where Scala version of Future<T> is more flexible than the Java version as you can create futures directly from blocks of code,

…

14: Q84 – Q87 Category Theory With Scala Interview Q&As

Q84. What is a category theory from a functional programming language perspective? A84. The category theory is all about abstractions. Composition “f” and “g” are functions, and “A” and “B” are types. f: A => … Read more ›...

This content is for 30-Day-Full-Access, 100-Day-Full-Access, 200-Day-Full-Access, and 365-Day-Full-Access members only. Register 80+ Free Java FAQs 80+ Free Big Data FAQs

Already a member? Log in here

« 1 2 3 4 5 »

Blog Archives

11: Coding Scala Way – Actors with Akka – part 1

11A: Scala values, proper types, first order types & higher kinded types

11B: Q71 – Q72 – Scala type parameterization & variance interview Q&As

11C: Q73 – Q77 – Scala type parameterization & variance interview Q&As

11D: Scala existential type interview Q&As

12: Coding Scala Way – Actors with Akka “Ask Pattern” – Part 2

12: Q78 – Q80 Recursion in Scala Q&As explained with diagrams

13: Coding Scala Way – 2 Actors with Akka – part 3

13A: Scala Semigroup interview Q&As

13B: Q81 – Q83 Scala monoids interview Q&As

13B: Scala foldLeft, foldRight, scanLeft, scanRight, reduceLeft, reduceRight, etc are Monoids

14: Coding Scala Way – Scala concurrency with Future

14: Q84 – Q87 Category Theory With Scala Interview Q&As

300+ Java Interview Questions - FAQs

10+ Companion Techs Interview Q&As

300+ Big Data Interview Questions - FAQs

16+ Java Tech Key Areas Interview Q&As

Your Career Tips to go places

Tutorials on Java & Big Data

300+ Java Interview Questions Answered

Disclaimer