Scala Interview Questions and Answers for 10 years experience

1. What are the key differences between Scala and Java?

   • Answer: Scala is a functional programming language that runs on the JVM, offering conciseness, immutability features, and strong type inference. Java is an object-oriented language, generally more verbose. Scala supports both object-oriented and functional paradigms seamlessly, while Java is primarily object-oriented. Scala's type system is more sophisticated with features like type inference, variance, and higher-kinded types. Java's type system is simpler but less expressive. Scala offers features like pattern matching, case classes, and actors for concurrency, which Java lacks directly.

2. Explain immutability in Scala and its benefits.

   • Answer: Immutability means that once an object is created, its state cannot be changed. In Scala, this is achieved through `val` declarations. Benefits include simplified reasoning about code (no side effects), improved concurrency (no race conditions), and easier debugging (state is predictable).

3. What are case classes in Scala and why are they useful?

   • Answer: Case classes are a special kind of class in Scala that are designed for pattern matching and data structures. They automatically provide useful methods like `equals`, `hashCode`, `toString`, and `copy`. They are immutable by default and are ideal for representing data in a concise and efficient way.

4. Explain pattern matching in Scala. Give an example.

   • Answer: Pattern matching is a powerful feature in Scala that allows you to match values against a series of patterns. It enhances readability and reduces boilerplate code compared to traditional `if-else` statements. Example: ```scala val x = 10 x match { case 10 => println("x is 10") case _ => println("x is not 10") } ```

5. What are higher-order functions in Scala? Provide examples.

   • Answer: Higher-order functions are functions that take other functions as arguments or return functions as results. Examples include `map`, `filter`, `flatMap`, and `reduce`. They enable functional programming paradigms and code reusability. ```scala val numbers = List(1, 2, 3, 4, 5) val doubled = numbers.map(_ * 2) // map takes a function as argument ```

6. Explain the difference between `val` and `var` in Scala.

   • Answer: `val` declares an immutable variable; its value cannot be changed after initialization. `var` declares a mutable variable; its value can be changed after initialization. Prefer `val` whenever possible to promote immutability and code clarity.

7. What are traits in Scala and how are they different from abstract classes?

   • Answer: Traits are similar to interfaces in Java, but they can have implementation details. A class can mix in multiple traits. Abstract classes can also have implementation, but a class can only extend one abstract class. Traits are more flexible for code reuse and composition.

8. Describe how to handle exceptions in Scala.

   • Answer: Scala uses `try-catch-finally` blocks similar to Java. However, Scala also offers more functional approaches using `Option` and `Either` to handle potential failures instead of exceptions. This improves code readability and reduces reliance on exceptions for control flow.

9. Explain the concept of monads in Scala.

   • Answer: Monads are a type class that provides a way to sequence computations in a type-safe manner, especially when dealing with potentially failing computations. `Option` and `Either` are examples of monads in Scala. They provide methods like `flatMap` (often called `bind`) to chain operations while handling potential failures elegantly.

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