Scala Interview FAQs Archives | Page 2 of 5 | 800+ Java & Big Data Interview Q&As

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06: Scala Class Vs. Object and Companion object interview Q&As

Q1. Given the below Person.scala file with Person.calss, what will be the output?

package com.sbthello

//a class - you create instance of a class, which become objects
class Person(name: String, age: Int, salary: BigDecimal) {
   println("This is printed when the object is created " + this)
  
   def calcBonus(bonus: BigDecimal) : BigDecimal = salary + bonus
   
   def getNameLength():Int = name.length() 
 
}

object Test extends App {
  
  val person1 = new Person("John", 25, BigDecimal(250.00))
  
}

package com.sbthello

//a class - you create instance of a class, which become objects

class Person(name: String, age: Int, salary: BigDecimal) {

println("This is printed when the object is created " + this)

def calcBonus(bonus: BigDecimal) : BigDecimal = salary + bonus

def getNameLength():Int = name.length()

}

object Test extends App {

val person1 = new Person("John", 25, BigDecimal(250.00))

}

A1. It prints the below text as when a Scala class is instantiated the statements in the body are executed after the object is constructed via the constructor defined in the class signature itself as “Person(name: String,

…

06: Coding Scala Way – Reduce & Compose functions

Example #14: Reduce operations Given a list of functions as shown below, how will you go about applying all the functions in the list to each input number and sum the result of each function?


object TestFunctions extends App {

  //list of functions
  val sumFive: Int => Int = x => x + 5
  val multiplyTwo: Int => Int = x => x * 2
  val sum2: Int => Int = x => x + 2
  
  //input numbers
  val listOfNumbers = List(1, 2, 3, 4)
}

object TestFunctions extends App {

//list of functions

val sumFive: Int => Int = x => x + 5

val multiplyTwo: Int => Int = x => x * 2

val sum2: Int => Int = x => x + 2

//input numbers

val listOfNumbers = List(1, 2, 3, 4)

}

For example, applying all 3 functions to first number in the list “1” …...

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06C: Q33 – Q40 Scala Futures and Promises Interview Q&As

Q33. What is a “Future” object in Scala? Is it an immutable object? A33. A Future is a holder object that holds a value (i.e. success scenario) or an exception (i.e. failure) which may become available at some point. Future represents the result of an asynchronous computation. … Read more...

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07: Coding Scala Way – Regular Expressions

Example #16: Regular Expression Regular expression (aka regex) to identify numbers in a string. Invoking “findFirstIn” and “findAll” functions of the “Regex” class. “[0-9]+”.r is a short form instead of instantiating it as new Regex(“[0-9]+”).


import scala.util.matching.Regex

object RegexTest extends App {

  val numberPattern: Regex = "[0-9]+".r // .r is same as new Regex("[0-9]+")
  val address = "Suite 121, 79 Belmont Cresent"

  val result = numberPattern.findFirstIn(address)
  
  println(result) //Some(121)
  println(result.getOrElse("")) //121
  
  val result2 = numberPattern.findAllIn(address) //result2 is Regex.MatchIterator
  
  result2.foreach { x => println(s"found a number = $x") }

}

import scala.util.matching.Regex

object RegexTest extends App {

val numberPattern: Regex = "[0-9]+".r // .r is same as new Regex("[0-9]+")

val address = "Suite 121, 79 Belmont Cresent"

val result = numberPattern.findFirstIn(address)

println(result) //Some(121)

println(result.getOrElse("")) //121

val result2 = numberPattern.findAllIn(address) //result2 is Regex.MatchIterator

result2.foreach { x => println(s"found a number = $x") }

}

Output


Some(121)
121
found a number = 121
found a number = 79

Some(121)

121

found a number = 121

found a number = 79

Example #17: Pattern matching with regex Split the given email address into...

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07: Q41 – Q48 Scala Async and Actor System Interview Q&As

Q41. What is the purpose of the “async” macro in Scala? A41. The 2.11 and later versions of Scala include the ability to transform code during compilation by using macros. The “async” macro is one of them, which transforms sequential code that uses “Futures” … Read more ›...

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07: Scala Factory Method Pattern & Trait Vs Abstract classes

This extends the Scala Class Vs. Object and Companion object interview Q&As to implement the factory method.

Q1. What is a factory method pattern?
A1. It is an Object Oriented Programming design pattern to instantiate objects. For example,

…

08: Coding Scala Way – Recursion & Higher Order Function

Example #20: nth Fibonacci number

Q1 What is wrong with the following recursive approach to compute the nth Fibonacci number?
A1 It “hangs” for the larger values of “n” like 50.


object RecursionVsIteration extends App {

  //1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144
  //find nth fibonacci number
  def fibNaive(n: Long): Long = {
    if (n <= 1) n
    else fibNaive(n - 1) + fibNaive(n - 2)
  }

  println(fibNaive(8))   // 8th number is 21
  println(fibNaive(12))  // 12th number is 144

  println(fibNaive(50))  //....hangs

}

object RecursionVsIteration extends App {

//1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144

//find nth fibonacci number

def fibNaive(n: Long): Long = {

if (n <= 1) n

else fibNaive(n - 1) + fibNaive(n - 2)

}

println(fibNaive(8)) // 8th number is 21

println(fibNaive(12)) // 12th number is 144

println(fibNaive(50)) //....hangs

}

Q2 How about using an iterative approach as shown below?

…

08: Q19 – Q26 Scala Data Structures basics interview questions & answers

Q19. What is the use of Tuples in Scala? A19. A Tuple is an immutable collection that can hold objects of different types. In other words, it groups together logical collections of items without using a class. There are 22 Tuple class in Scala from Tuple1, … Read more ›...

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08: Q49 – Q58 Scala Implicits Interview Q&As

Q49A. What are implicits in Scals? A49A. Implicits in Scala has two related features. 1) Implicit Parameters 2) Implicit Conversions. In both cases the Scala compiler implicitly provides extra information to prevent compile errors. 1. Implicit Parameters The code without implicits:


object ImplicitParameters extends App {
  
  def sum(x: Int)(y: Int) = x + y
  
  println(sum(10)(5)) // ok
  println(sum(10))   //compile-error: missing argument
}

object ImplicitParameters extends App {

def sum(x: Int)(y: Int) = x + y

println(sum(10)(5)) // ok

println(sum(10)) //compile-error: missing argument

}

The code with implicit parameters: Implicit parameters are...

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09: Coding Scala Way – Fibonacci Series

Example #22: Fibonacci series in Scala This extends determine the nth fibonacci number using Scala. In this let’s print the Fibonacci series of length n.


import scala.annotation.tailrec

object Fibonacci extends App {
  
   val zero = BigInt(0)
  
   def fibTail(n: Long): BigInt = {
     
    if (n <= 1) return 1 

    @tailrec
    def fibRecursion(a: BigInt, b: BigInt, n: BigInt): BigInt = {
      
      n match  {
        case `zero` => b  //wrap with "`" to match against a variable
        case _ => fibRecursion(b, a + b, n - 1)
      }    
    }
    
    fibRecursion(1, 1, n - 2)  
  }
   
  def fibSeries(n: Long) = (1L to n).map (n => fibTail(n)) 
  
  fibSeries(12).foreach {x => print(x + ", ") }
  
}

import scala.annotation.tailrec

object Fibonacci extends App {

val zero = BigInt(0)

def fibTail(n: Long): BigInt = {

if (n <= 1) return 1

@tailrec

def fibRecursion(a: BigInt, b: BigInt, n: BigInt): BigInt = {

n match {

case `zero` => b //wrap with "`" to match against a variable

case _ => fibRecursion(b, a + b, n - 1)

}

fibRecursion(1, 1, n - 2)

}

def fibSeries(n: Long) = (1L to n).map (n => fibTail(n))

fibSeries(12).foreach {x => print(x + ", ") }

}

Output:


1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144,

1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144,

Q1 Is the above approach to “print the Fibonacci series of length n” … Read more ›...

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09: Q59 – Q65 Higher Order Functions in Scala Interview Q&As

Q59. What is a higher order function, and what is the purpose of higher order functions? A59. Higher-order functions are functions that take functions as parameters. This gives you opportunities to condense and simplify code. The most used methods in the entire Collection API like map, … Read more ›...

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10: Coding Scala Way – groupBy, mapValues & identity

Java developers need to learn Coding Scala Way. Scala way of coding is quite different & you need to unlearn Java way of coding

Question: Given a list of numbers, how will you group the numbers by how many times they occur? for example output for “List(3,

…

10: Q66 – Q70 Pattern matching in Scala Interview Q&As

Q66. What is the purpose of pattern matching in Scala? A66. It is for the “flow control“. Most imperative languages support “if-then-else”, case statements, and loops like while, for, foreach, etc. Scala does support some of these, but the most often used “ … Read more ›...

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« 1 2 3 4 5 »

Blog Archives

06: Scala Class Vs. Object and Companion object interview Q&As

06: Coding Scala Way – Reduce & Compose functions

06C: Q33 – Q40 Scala Futures and Promises Interview Q&As

07: Coding Scala Way – Regular Expressions

07: Q41 – Q48 Scala Async and Actor System Interview Q&As

07: Scala Factory Method Pattern & Trait Vs Abstract classes

08: Coding Scala Way – Recursion & Higher Order Function

08: Q19 – Q26 Scala Data Structures basics interview questions & answers

08: Q49 – Q58 Scala Implicits Interview Q&As

09: Coding Scala Way – Fibonacci Series

09: Q59 – Q65 Higher Order Functions in Scala Interview Q&As

10: Coding Scala Way – groupBy, mapValues & identity

10: Q66 – Q70 Pattern matching in Scala Interview Q&As

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