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Kotlin

30 August 2023

How to Get Started with Kotlin: A Step-by-Step Guide for Beginners

Learning a new programming language opens up new possibilities for your career and lets you build different types of applications. Kotlin is a modern, concise language that runs on the Java Virtual Machine (JVM) and can be used for Android development, web backends, desktop applications, and more.

This step-by-step guide will walk you through the fundamentals of Kotlin from installation to building real projects, providing numerous code examples along the way. By the end, you'll have the skills to start creating applications with Kotlin as a beginner.

This article is part of our Kotlin Training Course. 

What Exactly is Kotlin and Why Learn It?

Before we dive into learning Kotlin, let's understand what Kotlin is and why it's gaining popularity:

  • Created by JetBrains - Kotlin was developed by the software company JetBrains, known for IntelliJ IDEA and other development tools.
  • Statically typed - Like Java, Kotlin uses static types, meaning variables have a defined type at compile time. This leads to safer code.
  • Interoperable with Java - Kotlin code can seamlessly interface with existing Java code. Kotlin and Java files can co-exist within a project.
  • Concise syntax - Kotlin reduces boilerplate code and has an expressive syntax using features like type inference.
  • Functional programming support - Kotlin supports functional constructs like higher-order functions, making it great for reactive programming.
  • Null safety - The type system distinguishes between nullable and non-nullable types, avoiding pesky NullPointerExceptions.
  • Open source - Kotlin is free, open source and has an active community supporting it.

These features make Kotlin a modern, improved alternative to Java without introducing radical changes. Understanding Kotlin opens up opportunities for mobile and backend development roles.

Step 1 - Install the Kotlin Compiler and IDE Plugins

To write and run Kotlin applications, the first step is to setup the Kotlin compiler and tools on your development machine:

Install the Kotlin Compiler

You can install the Kotlin compiler directly from the Kotlin website. Downloads are available for macOS, Windows, Linux and other platforms.

Unzip the downloaded file to a directory on your system. Inside, you'll find the Kotlin compiler *.jar file along with useful scripts and examples.

Add the bin directory path to your system PATH to be able to invoke the compiler from anywhere.

Install the Kotlin Plugin for IntelliJ IDEA

IntelliJ IDEA is a popular Java IDE by JetBrains that works well for Kotlin development. Install the Kotlin plugin:

  1. Open IntelliJ IDEA and go to Preferences > Plugins
  2. Search for and install the Kotlin plugin

The plugin takes care of configuring Kotlin for your projects within IntelliJ.

Install the Kotlin Plugin for Eclipse

If you prefer Eclipse, install the Kotlin plugin for Eclipse from the JetBrains plugin repository. This will enable Eclipse for Kotlin application creation.

With the compiler and IDE support installed, let's write our first Kotlin program!

Step 2 - Hello World: Your First Kotlin Program

Traditionally, the first program you write in a new language prints out "Hello World". Here is how to do this in Kotlin:

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

Let's understand what's happening in this simple one-liner:

  • main() is the entry point function. Kotlin executes code inside main().
  • fun declares a function in Kotlin.
  • println() prints out text to the console.
  • Semicolons (;) can be omitted when separating statements on newlines.

To run the program, save it as hello.kt and run:

kotlin hello.kt

You should see "Hello World!" print out. With that simple program, you've already grasped some Kotlin fundamentals like functions, printing, and syntax! Let's move on to understand the building blocks of the language more deeply.

Step 3 - Learn Kotlin Language Basics: Syntax, Variables, Data Types

In this section, we will cover the essential concepts including:

  • Variables to store data
  • Data types like numbers, characters, booleans etc
  • Conditional logic using if and when
  • Loops using for and while
  • Functions to reuse code

These concepts power most of the programs you'll build in Kotlin. Let's look at them one-by-one:

Variables to Store Data

Use var and val keywords to declare mutable and read-only variables respectively:

var mutableVar = 0
val immutableVal = 1

Variables must be initialized at the time of declaration.

Kotlin Data Types

Kotlin supports the following commonly used data types:

  • Numbers: Int, Float, Double, Long etc
  • Characters: Char
  • Booleans: Boolean
  • Strings: String
  • Arrays: Array<Type>

For example:

val positiveNumber: Int = 5
val pi: Double = 3.14159  
val letter: Char = 'A'

Control Flow using if, else if, else

The if statement checks a condition and executes different code blocks based on boolean evaluation:

val x = 5

if (x > 0) {
  println("Positive")
} else if (x < 0) {
  println("Negative") 
} else {
  println("Zero")
}

if can be used as an expression that returns a value.

When Statement

The when statement is like switch in other languages, executing different code blocks based on the value:

when(x) {
  0 -> print("Zero")
  in 1..10 -> print("Positive") 
  else -> print("Negative")
}

For Loops

The for loop iterates over ranges, arrays, collections and more:

for (num in 1..10) {
  println(num) 
}

for (i in array) {
  println(i)
}

While Loops

The while loop executes code repeatedly as long as the condition is true:

var i = 0
while (i < 10) {
  println(i)
  i++ 
}

These essential language elements allow you to start solving programming problems in Kotlin. Next let's look at functions.

Step 4 - Functions in Kotlin: Reusable Code Blocks

Like most languages, Kotlin supports functions to reuse code:

fun main() {
  printNumber(5)
}

fun printNumber(x: Int) {
  println("The number is $x") 
}

Let's understand Kotlin function syntax:

  • fun declares a function
  • Names are in camelCase
  • Parameters have explicit types like x: Int
  • The function body goes inside {}
  • return is optional. The last statement is implicitly returned.

Now you can write reusable logic using functions!

Step 5 - Kotlin Classes: Object Oriented Programming

Along with functions, Kotlin supports classes and object-oriented programming:

class Person(val name: String, var age: Int)

fun main() {
  val person1 = Person("Kate", 20)
  println(person1.name) // Outputs "Kate"
  
  person1.age = 21
  println(person1.age) // Outputs 21
}

Key highlights of Kotlin classes:

  • class keyword defines a class
  • Constructor arguments can be used to initialize properties
  • val defines immutable properties, var defines mutable properties
  • Kotlin is interoperable with Java classes

Classes allow you to model real-world objects and entity relationships.

Step 6 - Build Your First Kotlin Application

With the basics covered, let's build a simple command line app that takes user input, does a calculation, and displays output.

We'll build an app that calculates simple interest based on user input:

fun main() {
  print("Enter principal: ")
  val principal = readLine()!!.toDouble()

  print("Enter interest rate: ")
  val rate = readLine()!!.toDouble()   

  print("Enter number of years: ")
  val years = readLine()!!.toInt()    

  val interest = principal * rate * years / 100

  println("Simple interest = $interest")
}

This covers several concepts:

  • Reading stdin input using readLine()
  • Converting using toDouble() and toInt()
  • Calculation using variables
  • String templates like $interest

You now have the ability to create complete Kotlin programs for real-world use cases!

Step 7 - Discover More Kotlin Features

This guide covered Kotlin fundamentals, but Kotlin has many more features you can learn:

  • Lambdas - Anonymous functions that can be passed as arguments
  • Null safety - Avoid null reference errors using nullable and non-nullable types
  • Extension functions - Add functions to existing classes
  • Generics - Parameterize types with generics like List<String>
  • Coroutines - Asynchronous programming like async/await

You can dive deeper into each topic and keep growing your Kotlin skills!

Step 8 - Learn Kotlin: Resources for Your Journey

Here are some resources to continue your Kotlin education:

  • Kotlin docs - Official programming guides
  • Kotlin Koans - Interactive programming exercises
  • Kotlin Conf - Annual Kotlin conference videos
  • Kotlin courses JBI Training - Customised courses articles and tutorials
  • r/Kotlin - Subreddit community for Kotlin developers
  • Kotlin Slack - Chat community with thousands of developers
  • JBI Training Blog - a continually updated Blog featuring articles and How-To guides in Kotlin.

The Kotlin community has published many high-quality resources that greatly simplify your learning process.

Step 9 - Next Steps in Your Kotlin Journey

Congratulations, you now have a solid foundation in the Kotlin language! Here are some next steps:

  • Practice by developing projects - Active practice is key for reinforcing language skills
  • Take advanced Kotlin courses - Dive deeper into coroutines, functional programming etc
  • Read Kotlin source code - Learn from open source Kotlin projects on GitHub
  • Join online Kotlin communities - Connect with other Kotlin developers
  • Build mobile apps in Kotlin - Create Android apps using Kotlin
  • Use Kotlin for backend development - Write web services, build frameworks in Kotlin

Kotlin is a skill that will serve you well for both mobile and server-side development. As you learn and apply Kotlin, remember that becoming a proficient developer takes time and practice. Be patient with yourself, keep coding, and have fun!

Frequently Asked Questions

Here are some common questions about getting started with Kotlin:

Should I learn Kotlin or Java first?

Kotlin is a great alternative to Java. Learning either first will enable picking up the other quickly. Kotlin has a gentler learning curve.

What IDE is best for Kotlin?

IntelliJ IDEA is excellent for Kotlin development thanks to built-in tooling support via the Kotlin plugin. Android Studio and Eclipse also work well.

Can I use Kotlin for frontend web development?

Kotlin can compile to JavaScript, enabling frontend development. Consider using Kotlin/JS frameworks like React or Angular.

Is Kotlin good for backend development?

Yes, Kotlin is great for server-side development. It runs on the JVM and can reuse Java libraries. Some popular frameworks are Spring Boot, Ktor and Vert.x.

What companies use Kotlin?

Many top tech companies use Kotlin including Google, Pinterest, Coursera, Netflix, Uber and Square. Its adoption continues to grow.

Conclusion

Kotlin is a modern, versatile programming language that makes development faster and more fun. This step-by-step guide walked you through the fundamentals of Kotlin syntax, object-oriented features, building applications and more.

With these Kotlin basics, you can start tackling real projects. Kotlin has a gentle learning curve while teaching you skills that apply anywhere Java is used. The language improves developer productivity and makes creating applications safer.

Now that you have a Kotlin foundation, you can constantly build on it through practice, taking courses, joining communities and exploring frameworks. Your journey to learn Kotlin has just begun!

Check out our next article on Kotlin for Advanced Programmers: Take Your Skills to the Next Level

In the contemporary landscape of dynamic infrastructure environments, Kotlin emerges as an indispensable asset for both operations teams and developers. Its capacity to eloquently define, create, and manage infrastructure as code establishes a foundation for enhanced efficiency and collaborative infrastructure administration.

Whether initiating an exploration of infrastructure-as-code or enhancing an existing Kotlin-based setup, our comprehensive training modules at JBI Training stand ready to facilitate your mastery of this robust framework. Delay no more; adopt the prowess of infrastructure-as-code to revolutionize your infrastructure workflows without delay.

Initiate your educational journey now with the Kotlin courses at JB International and unlock the boundless potential of infrastructure-as-code at your disposal. Our offerings include:

  • Kotlin: This course is tailored for individuals embarking on their Kotlin journey. Learn the fundamentals of Kotlin programming, understand its syntax, data structures, and object-oriented principles. Acquire the skills necessary to develop efficient and concise code in Kotlin.
  • Kotlin Best Practices: Elevate your Kotlin expertise by delving into best practices. Discover how to write clean, maintainable, and performant Kotlin code. Explore design patterns and idiomatic approaches that optimize your codebase for readability and efficiency.
  • Kotlin Beyond the Basics: Ready to take your Kotlin skills to the next level? This advanced course covers topics such as coroutines, advanced functional programming, and integrating Kotlin with other technologies. Harness the full potential of Kotlin to build sophisticated and robust applications.

Enrol in these courses and embark on a transformative journey to harness the power of Kotlin and infrastructure-as-code. Empower yourself to create, manage, and optimise digital infrastructures with confidence and expertise.

About the author: Daniel West
Tech Blogger & Researcher for JBI Training

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