If you are looking to attend a Scala interview, you might be busy reviewing the interview questions. Well, you have landed in the right place. In this article, you will gain an understanding of the Scala interview questions. Also, these are the frequently asked interview questions that are curated by the experts. As most organizations are looking for the expertized individuals, you will be the one who can grab the job opportunity. Let’s get started!
Ans: Scala is referred to as a Java-based Hybrid programming language. It is a combination of the features of both object-oriented and functional-oriented programming languages. It is utilized by the integration with the Java Virtual machine and is capable of compiling the written code.
Below is the list of advantages of using Scala:
High testability
High scalability
High maintainability and productivity
Less error-prone functional style
Provides features of concurrent programming
Includes functional and Object-Oriented
It does not include any Boilerplate code
Provides Singleton objects as a cleaner solution than Static
Scala Arrays utilize regular Generics
Scala includes native tuples and concise code
Ans: There are two types of Variables in Scala:
Mutable Variables – The mutable variables are those variables that have values that are capable of supporting changes (new values can be assigned to them once they are created). The mutable variables are declared by using the ‘var’ keyword.
Immutable Variables – Immutable variables are those variables that have values that cannot be changed once they are created. The mutable variables are declared using the ‘val’ keyword.
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Ans: A Scala map is referred to as a collection of key-value pairs. The values will be retrieved by using a key. The keys are unique while the values in the map not unique.
The Scala Map is considered as the set or the collection of the variables. It includes keys and values. The keys are used to retrieve the values. The values will not be unique in the Scala map, while the keys will be unique. Like the variables, a Scala map can be either mutable or immutable.
Ans: Below listed are the different features available in Scala.
Immutability: Scala makes use of the immutability concept. Immutable data will help in managing the concurrency control that requires management of the data.
Type inference: In Scala, there is no need to mention the data type and function return type explicitly.
Rich set of collections: Scala is capable of providing a rich set of collection libraries. It includes the classes and traits in order to collect data. These collections can be either immutable or mutable.
Singleton object: Scala makes use of a singleton object, which will be a class essentially which consists of only one object in the source file.
Case classes and Pattern matching: In Scala, case classes provide their extensible support to pattern matching. Hence, you are allowed to write a lot of logical coding.
String interpolation: String interpolation in Scala is responsible for allowing the users to embed the variable references directly in the processed string literals.
Concurrency control: Scala has come up with a standard library that consists of the actor model. You are allowed to write the concurrency code by using the actor.
Lazy computation: In Scala, computation is said to be lazy by default. You are allowed to declare a lazy variable by using the lazy keyword. The lazy computation is used to improve the performance.
Higher-order function: The higher-order function in Scala will allow you to create the lambda function, function composition, or an anonymous function, etc.
Traits: A trait is considered to be like an interface with a partial implementation. In Scala, the trait is referred to as the collection of abstract and non-abstract methods.
Rich set of collections: Scala is capable of providing a rich set of collection libraries. It includes the classes and traits in order to collect data. These collections can be either immutable or mutable.
Ans: There is no break statement in Scala, however, you can perform it by using the brake method and also importing Scala.util.control.Breaks._ package. This importing package can break your code.
import scala.util.control.Breaks._ // Importing package
object MainObject {
def main(args: Array[String]) {
breakable { // Usage Of the breakable method to avoid exception
for(i<-2 to 10 by 2){
if(i==9)
break // Usage of break
else
println(i)
}
}
}
} Ans: A Tuple in Scala is specifically used to combine a fixed and finite number of items together which is capable of allowing the programmer/coder to pass a tuple as a whole. Tuples are capable of holding the objects that include the data types that are varying and also immutable.
Tuples are used to represent the combination of finite inputs. Tuples are used to combine a fixed number of items together. This provides flexibility to the programmer in order to integrate the discrete items into a whole. Tuples are considered as immutable but can combine items of different types together.
Ans: There are three different types of scopes that are based on their use namely:
Fields: Fields are those variables that are declared inside an object and they are allowed to be accessed from anywhere inside the program based upon the access modifiers. Fields can be declared either by using var as well as val.
Method Parameters: Method parameters are considered to be strictly Immutable. Method parameters are those parameters that are mainly used to pass the values to the methods. The method parameters can be accessed inside a method, but it is also possible to access them from outside the method that will be provided by a Reference.
Local Variables: Local variables are those variables that are declared inside a method and they are allowed to be accessed only inside the method. They can be accessed if you return them from the method.
Ans: You will need to extend a base Scala class and you can also design an Inherited class in the same way you do it in Java by using extends keyword. However, there are two restrictions: method Overriding will require the override keyword, and only the Primary constructor can pass parameters to the base Constructor. Let us get a clear understanding with the following example
println("How do you extend the abstract class Parent and define a subclass of parent called child")
class Child=(name:String)extends Parent(name){
override def printName:Unit= println(name)
}
object Child {
def apply(name:String):Parent={
new Child(name)
}
}Ans: Monad is one of the other fascinating features of Scala which provides the ability of one object to wrap with another object. This feature is only possible using a Monad. A monad is referred to as an object which consists of the functions that can be directed for the manipulation of the underlying objects. Monad does not apply the program to the objects directly.
Ans: A Trait is referred to as a particular unit of Class that provides the flexibility to use multiple inheritances. It also allows the encapsulation of a method along with its variables and fields. A class can include multiple traits while a trait is capable of extending only one class.
Ans: Throw Exception: Throwing an exception is similar to the way it looks in Java. It is possible to create an exception object and then you need to throw the same using the throw keyword which can be represented as follows.
Throw new IllegalArgumentException
Catching an Exception:
Scala provides the flexibility to either use try/catch any exception in a single block and then it is needed to perform the pattern matching against it using case blocks. Below is an example of the program to handle the exception.
import java.io.FileReader
import java.io.FileNotFoundException
import java.io.IOException
object Demo {
def main(args: Array[String]) {
try {
val f = new FileReader("input.txt")
} catch {
case ex: FileNotFoundException ={
println("Missing file exception")
}
case ex: IOException = {
println("IO Exception")
}
}
}
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Ans: Below is the methods that can be used to create the arrays in Scala:
ofDim can be used to declare the multidimensional arrays.
var myMatrix = ofDim[Int](4,4)
The Range() method can be used for the generation of an array that contains a sequence of increasing integers in a given range.
def range( start: Int, end: Int, step: Int ): Array[Int]
range (10, 20, 2)
Ans: The Syntax for function declaration can be represented as follows:
def functionName ([list of parameters]) : [return type] = {
function body
return [expression]
}In the above syntax, the return type will be any valid Scala data type and we can separate the list of parameters by using a comma and list of parameters and return type is optional. We use a return statement along with an expression in case the function returns a value and it works similarly, like in Java.
Ans: Below represented are a few String Methods that are available in Scala.
String[] split(String regex): This string method will help in splitting the string around matches of the given regular expression.
String toUpperCase: This method will be converting all of the characters in this String to uppercase by considering the rules of the given Locale.
Int length(): This method will return the length of this string.
tring trim(): This method will return a copy of the string, with leading and trailing whitespace omitted.
Char[] to CharArray(): This method helps in Converting the string to a new character array.
Ans: There are three types of loops that are available in Scala.
Do-While: It is similar to the while statement except that it will be testing the condition at the end of the loop body.
For: The for will be executing a sequence of statements multiple times and abbreviated the code that manages the loop variable.
While Loop: The while loop will be repeating the set of statements or group of statements while a given condition is true. It tests the condition before performing the execution of the loop body..
Break: Break is a loop control statement that is responsible for terminating the loop statement and transferring the execution to the statement immediately following the loop.
Ans: The three important and default Packages that are available in Scala are as follows:
Java.io._ : Java.io._ Package is used to import every class in Scala for input-output resources.
Java.lang._ : Java.lang._ package in Java is flexible to provide the classes that are fundamental to the design of the Java programming language.
PreDef: Predef provides type aliases for types that are frequently used such as the immutable collection types Map, Set, and the List constructors
Ans: The Anonymous functions are called ‘Function literals’ in the Source code, and at run time, function literals are instantiated into objects called as the Function values. Scala provides an easy syntax to define the anonymous functions.
//Syntax
(a:Int, b:Int)=> a*b
Or
(_:Int)*(_Int)Ans: These terms generally sound to be similar, however, there is a difference between them.
Nil refers to the end of a List.
Null states the value is not present. It is more particularly the absence of type information for the complex types that are inherited from AnyRef.
None denotes the value of an option that does not have any value inside it.
Nothing represents the lowest type – all values under AnyRef and AnyVal will fall under this umbrella.
Ans: Whenever we take a particular task and break it into subtasks to perform the execution at one time by using the multiple threads, we call it parallelism. Concurrency is different from parallelism. Concurrency comes into the picture when multiple computations are executed sequentially; this happens during the overlapping time periods. When we avoid access to a particular mutable state by multiple threads at a time, it is concurrency. Sometimes, actors can concurrent as well as parallel. Node.js follows a single-threaded implementation yet is concurrent because of its event loop. A simple example of parallelism is the parallel collections.
Ans: The compiler is not capable of randomly looking for simplicity in your code; it follows the following precedence:
Locally declared implicit
Imported implicits
Outer scope (ex- a class for a method)
Inheritance
Package object
An implicit scope like companion objects
Ans: Scala stands for SCAlable LAnguage. The father of Scala is Martin Odersky.
Scala is referred to as a Multi-Paradigm Programming Language, which provides its extensible support for both Object-Oriented and Functional Programming concepts. Scala is also called a Type-Safe Object-Functional Programming JVM Language. Scala is flexible and compatible to run on JVM(Java Virtual Machine).
Scala is also called a Hybrid Functional (Object-Oriented and Functional) Programming JVM Language. Scala has a strong and statically type System. In Scala, all types will be checked during the compile-time
Ans: We have seen the multiple advantages and benefits of scala, however, it also has one major Drawback which is the Backward Compatibility Issue. If we want to upgrade to the latest version of Scala, then you need to be particular and ensure to take care of changing some package names, class names, method or function names, etc.
For example, If you are using the old Scala version and your project is using BeanProperty annotation. It was available in “scala.reflect” like “scala.reflect.BeanProperty” in old versions. If you want to upgrade to a new Scala version, then you need to change this package from “scala.reflect” to “scala.beans”.
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Ans: Type inference is referred to as the process in which the types can be inferred by the Scala Compiler at compile-time. Types here refer to the data type or result type. We make use of the Types at different places in Scala programs like Method/Function Parameter types, Object types, Method/Function return types, Variable types, etc.
In simple words, identifying or determining the type of a variable or expression or object,etc during the compile-time by the compiler is known as “Type Inference”.
Ans: Both val and var are used to define variables in scala. However, they have some significant differences.
var stands for the variable.
val stands for value.
The variable can be changeable while the value remains constant.
var is used for defining the mutable variables which means that we can reassign values once it is created.
val is used for defining the immutable variables which means we cannot reassign values once it is created.
In simple Java terminology, var refers to the ‘variable’ and val refers to the ‘final variable’.
Ans: Java is not capable of providing its support to Operator Overloading. Scala provides its extensible support to Operator Overloading.
The main reason is that Java does would not like to support some misleading method names like “+*/”. Scala has come up with this flexibility to developers to decide which methods/function names should be used.
When we call 3 + 5 that means ‘+’ is not an operator, it is a method that is available in Int class (or it’s implicit type). Internally, this call is converted into “3.+(5)“.
Ans: There are various frameworks supported by Scala that include the following.
Ans: A stream is referred to as a Lazy list, that helps in the evaluation of the elements only when they are required.
Ans: The different operators in Scala include the following.
Ans: A Set is referred to as a collection that contains unique elements (no duplicates). There are two different types of sets. They are: mutable and immutable (its value cannot be changed). By default, Scala makes use of immutable sets. Few methods for set operations are:
head: head will return the head (first element) of the set
isEmpty: will check if the set is empty, returns Boolean
tail: tail will be returning the entire set except for the head element
Ans: A bitSet is referred to as a collection of smaller integers that are represented as bits of the larger integer. We are allowed to add the multiple items in a bitset using the ‘++’ operator that is similar to the list. Bitsets can either be mutable and immutable and considered to be the sets of non-negative integers.
With this, we are at the end of the Scala interview questions article. By this time, you might have got an idea of the most frequently asked questions in scala which would definitely help you in achieving the job roles and career you desire. All the best!
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