Scala Interview Questions and Answers
Intermediate / 1 to 5 years experienced level questions & answers
Ques 1. Explain pattern matching in Scala.
Pattern matching is a powerful feature in Scala that allows you to match complex data structures, making code more concise and readable.
Ques 2. What is the purpose of the 'apply' method in Scala?
The 'apply' method is a special method in Scala that is invoked when an object is called like a function. It is often used to create objects without using the 'new' keyword.
Ques 3. What is the difference between 'map' and 'flatMap' in Scala?
'map' applies a function to each element of a collection and returns a new collection of the results, while 'flatMap' applies a function that returns a collection to each element and flattens the results into a single collection.
Ques 4. Explain the concept of immutability in Scala.
Immutability means that once an object is created, its state cannot be changed. In Scala, 'val' and immutable collections are used to create immutable data structures.
Ques 5. What is a companion object in Scala?
A companion object is an object with the same name as a class and is defined in the same file. It is used to contain static methods and properties related to the class.
Ques 6. What is a trait in Scala?
A trait is a collection of abstract and concrete methods that can be mixed into classes to provide additional functionality. Unlike classes, a class can extend multiple traits.
Ques 7. Explain lazy evaluation in Scala.
Lazy evaluation is a strategy where the evaluation of an expression is delayed until its value is actually needed. It can improve performance by avoiding unnecessary computations.
Ques 8. What are case classes in Scala?
Case classes are regular classes with some additional features. They are often used for immutable data modeling and come with built-in support for pattern matching.
Ques 9. What is a partial function in Scala?
A partial function is a function that is not defined for every input value. It is defined only for a subset of possible input values using the 'isDefinedAt' method.
Ques 10. What is the 'implicit' keyword used for in Scala?
The 'implicit' keyword is used to declare that a value can be automatically passed to a method or function parameter. It is often used in combination with implicits.
Ques 11. Explain the concept of type bounds in Scala.
Type bounds restrict the possible types that can be used as type parameters. They include 'Upper bounds' denoted by <: and 'Lower bounds' denoted by >:.
Ques 12. Explain the concept of implicit conversions in Scala.
Implicit conversions allow the compiler to automatically convert one type to another if needed. They are defined using the 'implicit' keyword and are commonly used for enhancing existing types with new functionality.
Ques 13. What is the 'sealed' keyword used for in Scala?
The 'sealed' keyword is used to restrict the inheritance of a class to the same file. It helps the compiler exhaustively check pattern matches, ensuring that all possible subclasses are covered.
Ques 14. What is the 'View' in Scala collections?
The 'View' in Scala collections provides a lazy and non-strict version of a collection. It allows you to create a lightweight view on a collection without creating a new data structure.
Ques 15. How does Scala support multiple inheritance?
Scala supports multiple inheritance through the use of traits. A class can extend multiple traits, allowing it to inherit behavior from each of them.
Ques 16. What is the purpose of the 'withFilter' method in Scala?
The 'withFilter' method is used in conjunction with 'for' comprehensions to enable lazy filtering of elements in a collection. It is similar to 'filter' but is evaluated lazily.
Ques 17. What is the purpose of 'scalatest' in Scala?
'scalatest' is a popular testing framework for Scala. It provides a rich set of features for writing and executing tests, including support for behavior-driven development (BDD) and various testing styles.
Ques 18. What is the purpose of the 'unapply' method in Scala?
The 'unapply' method is used in the context of pattern matching. It allows you to extract values from objects, making it a key component in creating custom extractors for pattern matching.
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