Scala - Interview Questions and Answers

41) What is exception propagation in Scala?

In Scala, you can propagate the exception in calling chain. When an exception occurs in any function, it looks for the handler. If handler not available there, it forwards to caller method and looks for handler there. If handler presents there, handler catch that exception. If the handler does not present, it moves to next caller method in calling chain. This whole process is known as exception propagation.

42) What are throws in Scala?

Scala provides throws keyword for declaring the exception. You can declare an exception with method definition. It provides information to the caller function that this method may throw this exception. It helps to caller function to handle and enclose that code in a try-catch block to avoid abnormal termination of the program. In Scala, you can either use throws keyword or throws annotation to declare the exception.

Example

 class ExceptionExample4{     @throws(classOf[NumberFormatException])     def validate()={         "abc".toInt     } }  object MainObject{     def main(args:Array[String]){         var e = new ExceptionExample4()         try{             e.validate()         }catch{             case ex : NumberFormatException => println("Exception handeled here")         }         println("Rest of the code executing...")     } } 

43) What is a custom exception in Scala?

In Scala, you can create your exception. It is also known as custom exceptions. You must extend Exception class to while declaring custom exception class. You can create your message in custom class.

Example

 class InvalidAgeException(s:String) extends Exception(s){} class ExceptionExample{     @throws(classOf[InvalidAgeException])     def validate(age:Int){         if(age<18){             throw new InvalidAgeException("Not eligible")         }else{             println("You are eligible")         }     } } object MainObject{     def main(args:Array[String]){         var e = new ExceptionExample()         try{             e.validate(5)         }catch{             case e : Exception => println("Exception Occured : "+e)         }     } } 

44) What is a collection in Scala?

Scala provides a rich set of collection library. It contains classes and traits to collect data. These collections can be mutable or immutable. You can use them according to your requirement.

45) What is traversable in Scala collection?

It is a trait and used to traverse collection elements. It is a base trait for all Scala collections. It contains the methods which are common to all collections.

46) What does Set in Scala collection?

It is used to store unique elements in the set. It does not maintain any order for storing elements. You can apply various operations on them. It is defined in the Scala.collection.immutable package.

Example

In this example, we have created a set. You can create an empty set also. Let's see how to create a set.

 import scala.collection.immutable._ object MainObject{     def main(args:Array[String]){         val set1 = Set()    						// An empty set         val games = Set("Cricket","Football","Hocky","Golf") 	// Creating a set with elements         println(set1)         println(games)     } } 

47) What does SortedSet in Scala collection?

In Scala, SortedSet extends Set trait and provides sorted set elements. It is useful when you want sorted elements in the Set collection. You can sort integer values and string as well.

It is a trait, and you can apply all the methods defined in the traversable trait and Set trait.

Example

 import scala.collection.immutable.SortedSet             object MainObject{     def main(args:Array[String]){         var numbers: SortedSet[Int] = SortedSet(5,8,1,2,9,6,4,7,2)         numbers.foreach((element:Int)=> println(element))     }    } 

48) What is HashSet in Scala collection?

HashSet is a sealed class. It extends AbstractSet and immutable Set trait. It uses hash code to store elements. It neither maintains insertion order nor sorts the elements.

Example

 import scala.collection.immutable.HashSet object MainObject{     def main(args:Array[String]){         var hashset = HashSet(4,2,8,0,6,3,45)         hashset.foreach((element:Int) => println(element+" "))       } } 

49) What is BitSet in Scala?

Bitsets are sets of non-negative integers which are represented as variable-size arrays of bits packed into 64-bit words. The largest number stored in it determines the memory footprint of a bitset. It extends Set trait.

Example

 import scala.collection.immutable._ object MainObject{     def main(args:Array[String]){         var numbers = BitSet(1,5,8,6,9,0)         numbers.foreach((element:Int) => println(element))     } } 

50) What is ListSet in Scala collection?

In Scala, ListSet class implements immutable sets using a list-based data structure. In ListSet class elements are stored internally in a reversed insertion order, which means the newest element is at the head of the list. This collection is suitable only for a small number of elements. It maintains insertion order.

Example

 import scala.collection.immutable._ object MainObject{     def main(args:Array[String]){         var listset = ListSet(4,2,8,0,6,3,45)         listset.foreach((element:Int) => println(element+" "))     } } 

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