Scala interview questions are set to evaluate your proficiency in the programming language. You must thoroughly practice basic and advanced Scala concepts, including Spark Scala coding interview questions. If you are preparing for a web developer or software engineering interview, these Scala interview questions will provide you with an insight into the types of questions that will be asked.

Scala originated as a general-purpose programming language and continues to rise to prominence in today's big data industry with its phenomenal capabilities. Top FAANG+ companies, including Netflix, Twitter, LinkedIn, have deeply integrated Scala into their architecture and design, considering its high-level scalability and ability to handle petabytes of data. 

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Here's what we'll cover in the article:

• Basic Scala Interview Questions 
• Scala Interview Questions for Experienced Developers
• Scala Coding Interview Questions for Practice
• FAQs on Scala Interview Questions

Basic Scala Interview Questions

Scala can be your language of choice when there is a need to navigate a complex domain. Here are some Scala interview questions that will help you brush up on some vital Scala topics. 

1. What are some of the frameworks that Scala supports? 

Scala supports the following frameworks:  

• Spark Framework
• Play Framework
• Akka Framework
• Scalding Framework
• Neo4j Framework

2. What are the benefits of using Scala?

You must know that this is one of the most asked Scala interview questions. Scala offers attractive features and many positive attributes. Some key features are: 

• Its functions, macros, and tuples enhance the performance and make coding easier. 
• It is comparatively easier to learn. 
• It is a more concise, readable, and error-free programming language.  
• Scala ensures security and consistency in statistical abstraction by using an expressive typing system. 
• It allows you to build fault-tolerant and highly concurrent systems.
• Scala gels well with Apache Spark Ecosystem and proves ideal for data analytics.
• Scala supports concurrency and thus enables parallel processing.

3. What do you understand about the Scala set and Scala map? 

A collection of the same type of pairwise elements is called a Scala set. This set does not contain any duplicate elements. Scala sets are of two kinds: mutable and immutable.

A collection of key or value pairs is called a Scala map. Any value can be retrieved based on its key as keys are unique in the map while values are not.

4. What is the recursion tail in Scala?

The recursion function calls itself. In Scala, a recursive function is tail-recursive if the recursive call is the last operation performed by the function. So, you do not have to keep a record of the previous state. You can use @tailrec and check if the recursion is tail-recursive or not. 

5. What are tuples used for in Scala?

The tuples in Scala combine a fixed number of items to be passed around as a whole. It is immutable. You must know unlike an array or list, a tuple can hold objects of different types. 

6. What is function currying in Scala?

Currying in Scala is a simple technique of transforming a function. It takes multiple arguments into a function that takes a single argument. The main advantage of using the currying function is that it makes the code easier to refactor. However, this function is not much used by programmers.

7. What are the different types of Scala identifiers?

This is also one of the frequently asked Scala interview questions. The main Scala identifiers are:

• Operator identifiers
• Alphanumeric identifiers
• Mixed identifiers
• Literal identifiers

What are the different types of Scala literals?

The various types of Scala literals are:

• Boolean literals
• Symbol literals
• Integer literals
• Character literals
• Floating-point literals
• Multi-line strings 
• String literals

Scala Interview Questions For Experienced Developers

You must practice Scala developer interview questions if you are preparing for web applications developer positions or other related job roles. Top companies look for Scala specialists as this programming language is gaining wide popularity in functional program development as well as object-oriented applications. 

Here are some most commonly asked Scala interview questions and answers to help you in Scala interview prep:  

1. What is an auxiliary constructor?

All constructors other than the primary constructor are called auxiliary constructors in Scala. They are used for constructor overloading. It must call either previously defined auxiliary constructors or primary constructors present in the first line of its body.

2. How are 'apply' and 'unapply' methods used in Scala?

In Scala, an extractor object defines an unapply() method and apply() method. These two methods are used for mapping and unmapping data between form and model data. 

• Apply() method is used for assembling an object from its components. 
• Unapply() method follows the reverse order of apply order. So, this method decomposes an object into components. 

3. What do you mean by ofDim()?

The ofDim function in Scala declares multidimensional arrays using the matrix format. An Array.ofDim is used to declare multidimensional arrays, and there is no limit to the number of dimensional arrays you can create. 

4. What do you understand about map() and flatMap()?

map() and flatMap() are high-order functions used while dealig with data structures in Scala.   

• map() method: It is similar to mapping operations in other programming languages. The map() method enables you to iterate over a collection and translate it into another collection. This is an exceptionally powerful method in Scala, where every element of the collection is transformed by applying a function to it.
• flatMap() method: It is similar to map(), except flatMap() removes the inner grouping of items to create a sequence. This method is a combination of the flatten and the map method. The result that you would obtain from the map method followed by the flatten method can be produced by flatMap(). 

5. What is Closure in Scala?

Scala closures are functions whose return values depend on the values of one or more free variables declared outside the closure function. The free variables are neither defined in the function nor used as a parameter. They are not even bound to a function with valid values.  

6. Why is the 'Static' keyword not used in Scala?

The 'static' keyword is not a part of Scala design because Scala is a pure object-oriented language. Usually, we can assess class members without creating an object by employing the 'static' keyword. However, this goes against the OOP principles. So, to make it purely object-oriented, Scala does not include this keyword.

6. What are Monads in Scala?

This is one of the most popular Scala interview questions. You must understand that a Monad is not a class or a trait in Scala; it is a concept. 

In Scala, a Monad represents an object that wraps another object. You pass the Monad programs to perform the data manipulation of an underlying object. So, you do not directly manipulate the object. 

Every step has an output that serves as input for subsequent steps in Monads. All Monads are not collections as some are used as containers too. The data types that implement map and flatMap() such as options and lists are Monads in Scala.

7. What is Scala Anonymous Function?

The standard Scala functions include a name, a return type, a list of parameters, and a body. Contrastingly, an anonymous function does not have a name. These are defined by a lightweight syntax and are referred to as function literals in the source. These function literals become objects called function values at run time. You can use anonymous functions in Scala to create inline functions.

8. What are some string methods in Scala?

This is also one of the Scala interview questions often asked in various technical interviews. A few string methods in Scala are as follows:

• String trim(): It returns a copy of the string while omitting the leading and trailing spaces in the string. 
• String toUpperCase(): This method converts all of the characters to uppercase in the string.
• Char[] toCharArray(): It converts string to a new character array.
• String[] split(String regex): It splits the string around matches of the given regular expression.
• Int length(): This method returns the length of the string.

9. Why is Scala preferred for Spark?

This is also one of the frequently asked Scala interview questions that tests your in-depth knowledge about Scala and Spark. Scala is preferred by developers for Spark as it makes it easy to go deeper into Spark's source code and get access to and implement all the latest features of the framework. 

A single complex line of Scala code can easily replace between 20 to 25 lines of Java code. It is portable. The robust interoperability between Scala and Java code makes it possible for developers to use their Scala code to access Java libraries directly. Also, Scala is a static-typed language and thus ideal for Spark. 

Scala Spark Interview Questions

Apache Spark is an open-source, fast computation technology that is based on Hadoop and MapReduce. Its fast and efficient processing in-memory cluster computation are the main contributing features for its popularity. You must practice these commonly asked interview questions in Spark technology to equip yourself well for the interview: 

1. What are the best features of Apache Spark?
2. What does DAG refer to in Apache Spark?
3. What is YARN in Spark?
4. How is Apache Spark different from MapReduce?
5. What do you understand about Spark Datasets?
6. What is Spark DataFrames?
7. What is executor memory in Spark?
8. What is the worker node used for in Spark?
9. What are the disadvantages of using Spark in applications?
10. How can you minimize data transfers while working with Spark?

Scala Coding Interview Questions for Practice

You must practice Scala coding questions for your technical interview if you are applying to companies that prefer this programming language:

1. For a given number list and a number k, return whether any two numbers from the list add up to give k.
2. For a given array of integers, write a program in Scala to return a new array. Here, each element at index i of the new array is the product of all the numbers present in the original array except the one at i.
3. For a given root to a binary tree, write a program in Scala to implement 'serialize(root).' This root must serialize the tree into a string and deserialize(s) the string back into the tree.
4. For a given array of integers, how would you find the first missing positive integer in constant space and linear time? You have to find the lowest positive integer that does not exist in the array. (Note: The array can contain duplicates and negative numbers.)
5. For a given string, write a function to reduce it to its shortest length by implementing several operations, wherein you select a pair of matching adjacent lowercase and then delete them.

This completes our list of Scala interview questions. You must practice these well and learn how to answer them confidently in mock interviews.

FAQs on Scala Interview Questions

1. Are Scala Interview questions important for data engineers?

If you are applying for data engineering positions, you must practice Scala interview questions. Scala allows you to adopt a software engineering mindset, which is beneficial for your data engineering career. Scala is a type-safe language, and many big tech companies write a lot of pipelines in it. So, your knowledge of Scala gives you an upper edge in the interview.

1. What Scala interview questions should I prepare for front-end developer interviews?

Scala is mostly backend, but its Scala.js framework compiles to JS, and you can use it in the browser and other environments. You must prepare questions based on the Scala.js framework in addition to some basic Scala interview questions for front-end developer interviews.

1. Which companies prefer Scala software developers?

If you are a Scala developer, you can apply to top tech companies such as LinkedIn, Twitter, Foursquare, Netflix, Tumblr, The Guardian, AirBnB, Sony, and other tech giants. You must prepare well by practicing the most anticipated Scala interview questions as well as behavioral interview questions to ace the interview. 

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