Explore topic-wise InterviewSolutions in .

A simple program in Scala using Eclipse IDE 

• Step 1: Setup your Eclipse IDE for Scala development
• Step 2: In Eclipse, create a NEW Scala project
  From the File menu, select New -> Scala project and provide the project with a name.
• Step 3: Create a Scala object
  Create a new Scala Object using File -> New -> Scala Object and provide a name for your Scala application - > CLICK Finish to create the file.
• Step 4: Write your program code.

Example:  

• Step 5: Run the Scala program
  Click on the Run button or select Run from the menu to run the Scala application. If necessary, set the Run configuration.   
  Output:

With Scala, you can both develop functional PROGRAMS and Object-Oriented applications! Not so difficult, was it? As a result, the need for Scala specialists is growing worldwide. To gain access to the growing pool of job opportunities for Scala experts, you must first get a good score on the Scala Interview. To help you out, we have compiled a list of 35+ of the most commonly asked Scala interview questions and answers to provide some insight into what Scala interviewers are really interested in. For the freshers and experienced developers, these questions will be a great help in preparing for a software development job. For the pros, it will be a helpful tool for implementing improvements in their everyday coding practices. It should be noted that this list isn't exhaustive; Scala has several nuanced aspects that are better mastered with practice. 

Useful Resources:

Scala Documentation

Spark Interview

A Scala list is a collection of data stored as a linked list. In Scala, a list is IMMUTABLE, meaning it cannot be changed. To remedy this, Scala OFFERS List-Buffer. There are multiple ways to update a list and add new elements such as using the ":+" method: It adds new elements at the end of a list.  

Syntax:

Example: 

Output:  

var i = 0 while (j < ARGS.length) { println(args(i)) j++ }

Scala does not support the expression "j++" and should EITHER be REPLACED with “j+=1” or “j=j+1”.   

There are various types of inheritance supported by Scala, including single, multilevel, multiple, and hybrid. Single, multilevel, and hierarchy can all be applied to your class. Due to the fact that Scala doesn't allow multiple inheritances, Scala's trait comes into play to DEAL with the problem. TRAITS are defined in a SIMILAR manner to classes, except that they use the keyword trait RATHER than the class as shown below: 

The Scala team has not decided to use a "static" keyword as part of their DESIGN. This decision was taken primarily to make Scala a Pure Object-Oriented Language. USING the "static" keyword, we can even access class members without CREATING or using an object. This is totally against the OOP principles. For INSTANCE, Java does not qualify as a pure OO language since it supports the "static" keyword. 

Functions are first-class values in Scala and can be CREATED using the def keyword. When defining a function, the return type of the parameter must be SPECIFIED. A function's return type is optional. The default return type of a function is Unit if it is not specified. Function declarations in Scala have the following FORM: − 

When you don't use the EQUALS sign and the method body, methods are implicitly declared abstract. 

Example: 

Output: 

Using access modifiers, you can limit the scope to particular regions of code. Scala has three access modifiers: public, private, and protected. If you wish to use an access modifier, you must INCLUDE its keywords private/protected/public in the definition of a member of the package, class, or object. By default, the access modifier is public if neither of these keywords is USED. 

• Private: A private member can only be ACCESSED within a class that defines it or through one of its objects.
• Protected: Protected members are accessible from sub-classes of the class in which they are defined. This also applies to methods and variables.
• Public member: By default, the access modifier is public. In the ABSENCE of the private or protected KEYWORD, the compiler will treat the members as public, and it is not necessary to specify "public".

The default Scala packages are JAVA.lang, Java.io, and PreDef, each of which has varying FUNCTIONALITIES.  

• Java.lang: Fundamentally, Java.lang is a package containing classes compatible with the Java programming language.
• Java.io: You can import Scala classes for input-output resources with Java.io.
• PreDef: The PreDef package IMPLEMENTS type ALIASES for collections such as Map, Set, and LIST that are specifically immutable.

The implicit parameter, as OPPOSED to the regular parameter, can be passed silently to a method without going through the regular parameter list. The implicit keyword indicates these parameters and any parameters following the implicit keyword are implicit. Essentially, when we don't pass anything to methods or functions, the compiler will LOOK for an implicit value and use that as a parameter. Whenever implicit keywords appear in a function's parameter scope, this marks all parameters as implicit. Each method can simply have a single implicit keyword. 

Syntax:

Example: 

Output: 

SCALA USES the yield keyword in conjunction with the for LOOP. Following the completion of loop iterations, the yield keyword returns the result. For loops INTERNALLY store the iterated result in a buffer, and upon finishing all iterations, it yields the final result from that buffer. Maps, FlatMaps, Filters, and Nomads are all supported by Yield. 

Syntax:

Null, null, Nil, Nothing, None, and Unit are all used to represent empty values in Scala.   

• Null refers to the absence of data, and its type is Null with a capital N.  
• Null is considered to be a list that contains zero ITEMS. Essentially, it indicates the END of the list.  
• Nothing is also a trait WITHOUT instances.   
• None represents a sensible return VALUE. 
• Unit is the return type for functions that return no value. 

The constructors are responsible for initializing the state of the object. In the same way as methods, constructors also consist of statements/instructions that are executed when an object is created. Constructors are used in Scala to create INSTANCES of CLASSES. Scala has two types of constructors:  

• Primary Constructor: Scala programs often contain only one constructor, known as the primary constructor. It is not necessary to create a constructor explicitly SINCE the primary constructor and the class shares the same body.

Syntax:   

• Auxiliary Constructor: Auxiliary constructors are the constructors in a Scala PROGRAM other than a primary constructor. A program may contain any NUMBER of auxiliary constructors, but only one primary constructor.

Syntax: 

Scala supports tail recursion, which sets it apart from other languages. Recursion involves breaking a problem down into smaller sub-problems and calling itself to RESOLVE each of them. Simply put, recursion can be thought of as a function calling itself. Tail recursion REFERS to executing the last statement recursively.  As a result, these functions are more performant since they utilize tail call optimization. They do not add another stack frame to memory, but rather keep calling functions. If you are experiencing a stack OVERFLOW with your recursive functions, a tail-recursive function is your remedy. In addition, tail recursion makes your code faster and memory-constant.  

SYNTAX:

Example:

Output: 

In Scala, currying refers to the technique of transforming a function. There are multiple arguments passed into this function, which then forms a chain of functions that take one argument each. This type of function is widely used in multiple functional languages. 

 Syntax:

Example: 

Output: 

In this case, we've DEFINED an add function that TAKES two arguments (a and b), and it gives US the result of adding a and b, by calling it in the main function. 

Identification is done with the help of identifiers in programming languages. The identifiers in Scala are case-sensitive and can be class, method, variable, or object name. 

Example:  

As you can see from the above example, we have six identifiers:  

• InterviewBit: Class name
• x: Variable name
• Scaler: Object name
• main: Method name
• args: Variable name
• y: Object name

Types of Identifiers 

• Alphanumeric Identifiers: These identifiers start with a letter (capital/small) or underscore, followed by a DIGIT, letter, or underscore.
  Example: myVal , _Scaler , etc.
• Operator Identifiers: These identifiers contain ONE or more operator characters (such as +, :, ?, ~, or #, etc.).
  Example: +, ++ , etc.
• Mixed Identifiers: This type of IDENTIFIER consists of an alphanumeric identifier followed by an underscore and the operator identifier.
  Example: scaler_+ , myVal_= , etc.
• Literal Identifiers: In these identifiers, an ARBITRARY string is enclosed with backticks (`….`).
  Example: `Scaler` , etc.

SCALA TAKES the OPPOSITE approach; with functions, the arguments are val - i.e., immutable by default. This eliminates the need to type extra arguments. Scala is known for its use of immutability in design and in many cases, this is the default BEHAVIOR. Immutability's benefits include addressing equality issues and concurrency.

Standard functions generally include a name, a list of PARAMETERS, a RETURN type, and a body. An anonymous function is one for which a name is not given. In Scala, anonymous functions are defined by a lightweight syntax. In the SOURCE, anonymous functions are referred to as function literals, and at run TIME, these function literals become objects called function values. We can use it to create inline functions. 

Syntax: 

Despite being a simple topic, the MONAD belongs in the advanced SECTION of the Scala language. It is important to UNDERSTAND that a monad is not a class or a trait; it is a concept. Thus, a monad represents an object that wraps another object in Scala. Each step in Monads has an output that serves as input for SUBSEQUENT steps. Although Scala's maximum collections are Monads, yet not all Monads are collections. Some Monads, for example, can be used as containers like Options. To put it succinctly, the data TYPES that implement map and flatMap() (such as options, lists) in Scala are called monads.

Scala and Java are two of the world's most popular programming languages. Comparing Scala to Java, Scala is still a relatively new language. So, let us compare some of the differences between both of them. 

The concept of traits is similar to an interface in Java, but they are even more POWERFUL since they let you implement members. It is composed of both abstract and non-abstract methods, and it features a WIDE range of FIELDS as its members. Traits can either contain all abstract methods or a mixture of abstract and non-abstract methods. In computing, a trait is defined as a unit that encapsulates the method and its variables or fields. Furthermore, Scala allows partial implementation of traits, but no constructor parameters may be included in traits. To create traits, use the trait keyword. 

Syntax:

Example:  

Output:  

Scala closures are functions whose return value is dependent on one or more free variables declared outside the closure function. Neither of these free variables is defined in the function nor is it USED as a parameter, nor is it bound to a function with valid values. BASED on the values of the most RECENT free variables, the closing function is evaluated. 

Syntax: 

Example: 

Output: 

In the above program, the sum is a closure function. var x = 20 is an impure closure. As can be seen, x is the same, and y is different. 

Higher-order functions are functions in Scala that either take or return another function as an ARGUMENT or parameter. Another way to say it is a function that works with a function. You can create higher-order functions, lambda functions, or anonymous functions using a higher-order function.  

Example: In this case, the apply function contains another function a that is APPLIED to B. 

Output: