🚀 Kotlin – Get Started: Hello World & Your First Kotlin Program

🧲 Introduction – Starting Your Kotlin Journey

Ready to write your first lines of Kotlin? Whether you’re a beginner or transitioning from Java, starting with a simple Kotlin program like “Hello World” is the best way to understand the syntax, compiler behavior, and IDE workflow. Kotlin’s clear and concise structure makes it beginner-friendly and highly productive.

🎯 In this guide, you’ll learn:

• How to write and run your first Kotlin program
• The structure of a basic Kotlin file
• Differences between using Kotlin in CLI, IDEs, or online editors
• How the Kotlin main() function works

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💻 Your First Kotlin Program – “Hello, World!”

Let’s begin with the classic starting point in every language: printing “Hello, World!” to the console.

✨ Kotlin Hello World Example

fun main() {
    println("Hello, World!")
}

🔍 Code Breakdown:

Line	Explanation
fun main()	Declares the main function – the program’s entry point.
{ ... }	The code block that holds executable statements.
println()	Standard Kotlin function to print output to the console.

✅ Output:

Hello, World!

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🧰 How to Run Your First Kotlin Program

🟢 Option 1: Using IntelliJ IDEA

1. Open IntelliJ ➝ File ➝ New Project ➝ Kotlin ➝ Kotlin/JVM.
2. Create a file: Main.kt
3. Paste the Hello World code.
4. Click Run ▶️ or right-click → Run ‘MainKt’

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🟠 Option 2: Using Command Line (CLI)

1. Install Kotlin compiler CLI via SDKMAN or package manager.
2. Save code as hello.kt

kotlinc hello.kt -include-runtime -d hello.jar
java -jar hello.jar

✅ You should see: Hello, World!

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🌐 Option 3: Using Kotlin Playground (Online)

1. Visit https://play.kotlinlang.org
2. Paste the code and click Run

⚡ Instant output in your browser without setup.

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🧪 Writing a Slightly Advanced Program

Let’s modify the program to accept input and greet the user.

fun main() {
    print("Enter your name: ")
    val name = readLine()
    println("Hello, $name! Welcome to Kotlin.")
}

🔍 Code Explanation:

• print() – Prints without newline.
• readLine() – Reads user input from the console.
• $name – String template to embed variable inside text.

✅ Sample Output:

Enter your name: Arjun
Hello, Arjun! Welcome to Kotlin.

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📘 Structure of a Kotlin File

Kotlin Element	Example	Purpose
fun main()	Entry point	Starts the program
val / var	val name = "Kotlin"	Declares variables (immutable/mutable)
println()	println("Hi")	Outputs text to console
Comments	// single-line / /* */	Document your code
Blocks	{ ... }	Code grouping and scoping

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⚙️ Best Practices for Getting Started

Practice	Tip
✅ Use val by default	Promotes immutability unless change is needed
🔍 Use readLine() carefully	It returns nullable String (String?)
📂 Organize Kotlin files	Keep .kt files inside src directory in IDE
🚫 Avoid unnecessary semicolons	Kotlin does not require ; at line ends
🧠 Understand main()	It’s essential for CLI apps and learning syntax

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📌 Summary – Recap & Next Steps

You’ve just written your first Kotlin program and learned the structure of a basic Kotlin app. With just a few lines of code, Kotlin shows off its simplicity, readability, and developer-friendliness.

🔍 Key Takeaways:

• The main() function is the entry point for Kotlin applications.
• Use println() for output and readLine() for input.
• You can run Kotlin using IDEs, CLI, or online playgrounds.

⚙️ Practical Use:
From printing messages to taking input, Kotlin makes it easy to start writing programs—ideal for Android apps, backend systems, or scripting tasks.

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❓ FAQs – Kotlin First Program

❓ What is the main function in Kotlin?
✅ The main() function is the entry point for every Kotlin program. It’s where execution begins.

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❓ Do I need a class to run Kotlin code?
✅ No. Unlike Java, Kotlin doesn’t require wrapping your code inside a class for a basic program.

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❓ How do I run Kotlin code in a browser?
✅ Use Kotlin Playground to write and execute code instantly online.

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❓ Can Kotlin be run without IntelliJ?
✅ Yes. You can compile and run Kotlin from the command line using the kotlinc compiler and Java runtime.

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❓ What’s the difference between print() and println() in Kotlin?
✅ print() doesn’t add a newline at the end, while println() adds a newline after printing the output.

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