Introduction

Before you build classes, objects, or APIs, you need to understand the most basic building block: variables.

Scala makes a big deal about immutability, and this starts with how you declare data.

Let’s walk through the difference between val and var — and when to use them.

val – Immutable Value

val name = "Alice"
val age = 30

• ✅ Think of val like a final variable in Java or a const in JavaScript.
• ❌ You cannot reassign a val.

// This will cause a compilation error:
name = "Bob" // ❌ reassignment to val

• ✅ Use val by default — it makes your code safer and easier to reason about.

var – Mutable Variable

var count = 1
count = count + 1

• You can reassign var as needed.

Type Inference (and Explicit Types)

Scala can often infer the type of a value based on the assigned data:

val city = "Mumbai"   // Inferred as String
val score = 4.5       // Inferred as Double

But you can also write the type explicitly when you want to be more specific or improve readability:

val city: String = "Mumbai"
val score: Double = 4.5

This is especially useful in function signatures, public APIs, or when collaborating in a team.

Summary

Ready to go beyond online editors? Let’s set up Scala on your machine using IntelliJ IDEA.

🚀 Why IntelliJ IDEA?

JetBrains IntelliJ IDEA is one of the most powerful and developer-friendly IDEs out there, especially for JVM-based languages like Java and Scala.

It offers:

• ✅ Smart autocompletion and refactoring
• ✅ Built-in sbt support
• ✅ Great integration with Scala worksheets and test frameworks

🧰 Prerequisites

Before we start, make sure you have:

• ✅ Java SDK installed (JDK 8 or above)
• ✅ Internet connection to download IntelliJ and plugins

🧱 Step 1: Download and Install IntelliJ IDEA

👉 Go to https://www.jetbrains.com/idea/download
Download the Community Edition (it’s free and supports Scala with plugins).

Install it like any normal app.

🔌 Step 2: Install the Scala Plugin

1. Open IntelliJ IDEA
2. Go to Settings (or Preferences on macOS)
3. Navigate to Plugins
4. Search for Scala
5. Click Install
6. Restart the IDE

✅ Now IntelliJ knows how to compile and run Scala code!

📦 Step 3: Create a New Scala Project

1. Click on New Project
2. Choose Scala from the left menu
3. Under Build System, select sbt
4. Set your project name, location, and Scala version
5. Click Finish

Wait for sbt to download dependencies — it might take a minute.

📄 Step 4: Add a Simple Scala File

Inside src/main/scala, right-click → New → Scala Class → Name it HelloWorld

Paste the following code:

object HelloWorld {
  def main(args: Array[String]): Unit = {
    println("Hello from IntelliJ!")
  }
}

▶️ Step 5: Run Your Code

• Right-click inside the main method or on the file
• Choose Run HelloWorld

✅ You should see the output in the console: Hello from IntelliJ!

🧪 Bonus: Try a Scala Worksheet

Scala Worksheets allow you to write and evaluate code interactively. To create one:

• Right-click on your src folder
• Go to New → Scala Worksheet
• Name it Playground

Try typing:

val name = "Scala"
val version = 3.3
s"Hello $name $version"

You’ll see the result instantly on the right!

🎯 That’s It!

Now you have a full Scala development environment running locally with IntelliJ IDEA.

🔍 What’s Next?

Now that you’ve seen how easy it is to run Scala, here’s what you can do next:

👉 How to Define Variables

Scala might look intimidating at first, but let’s change that — one clean snippet at a time.

👋 Why Scala?

Scala combines the power of object-oriented and functional programming in one language. It runs on the JVM, making it a great fit for scalable, high-performance apps — but more importantly, you can just start small.

🛠️ Let’s Get Started — A Simple Hello World

Here’s how you write your first Scala program:

object HelloWorld {
  def main(args: Array[String]): Unit = {
    println("Hello, Scala!")
  }
}

🧠 What’s Happening?

• object is a singleton — like a class with only one instance.
• main is the entry point (just like in Java).
• println(...) prints to the console.

✅ To run this:

• Use the Scala REPL (via terminal or sbt console)
• Or paste it into Scastie: https://scastie.scala-lang.org and press ▶️ Run. That’s it!

🔍 What’s Next?

Now that you’ve seen how easy it is to run Scala, here’s what you can do next:

👉 Install Scala in IntelliJ IDEA – set up a real development environment