⚡ Scala Handbook

Overview

Scala is a strong statically typed JVM language that combines object-oriented and functional programming. It is widely used in big data (Apache Spark), distributed systems, and enterprise backends.

Platform JVM  Paradigm OOP + Functional  Typing Static, Inferred

Core Concepts

Variables

• val — immutable binding
• var — mutable binding
• Strong type inference — types usually omitted
• lazy val — evaluated on first access

Collections

• Immutable by default: List, Map, Set, Vector
• Mutable: ArrayBuffer, HashMap
• Rich higher-order: map, filter, flatMap, reduce, fold
• For-comprehensions as syntactic sugar

Functions & Higher-Order

• Functions are first-class values
• Currying: def add(x: Int)(y: Int) = x + y
• Partial application
• Pattern matching with match / case

Case Classes & Pattern Matching

• case class — immutable data with equals/hashCode/copy
• sealed trait for algebraic data types
• Option[T] — Some(x) | None
• Either[L, R] — Left | Right for error handling
• Try[T] — Success | Failure

Key Frameworks & Tools

Category	Framework / Tool
Big Data	Apache Spark
Streaming	Akka Streams, Apache Kafka + Akka
Web	Play Framework, http4s, ZIO HTTP
Concurrency	Akka Actors, ZIO, Cats Effect
Testing	ScalaTest, Specs2, MUnit
Build	sbt, Mill

Common Interview Topics

• val vs var vs lazy val
• Case class vs regular class
• Traits vs abstract classes
• Implicits and type classes
• Futures and async programming
• Scala with Apache Spark RDD/DataFrame/Dataset
• Functional error handling with Option/Either/Try