What is Kotlin?

Kotlin is an open-source, statically typed programming language that was released by JetBrains. It is an officially supported language for Android development that is used by many top companies like Twitter, Netflix, Uber, etc. It offers a precise, secure, and pragmatic language that is focused on interoperability with Java. 

Table of Contents

• What is Kotlin?
• History of Kotlin
• Where is Kotlin Used?
• How to Start with Kotlin?
• Difference between Java vs Kotlin
• Kotlin Basics
  • Data Types 
  • Variables
  • Constants
  • Arrays 
  • Conditionals (if-else)
  • Loops (for, while, do-while) 
• Functions
• Classes
• Objects and Companion Objects
• Constructors
• Visibility Modifiers
• Null Safety
• Smart Casts
• Extensions
• Lambda Expressions
• Standard Library
• Conclusion

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What is Kotlin?

Officially launched by JetBrains in 2011, Kotlin is a modern, concise, safe, and pragmatic programming language.

Mentioned below are some of the main features of Kotlin:

• Statically Typed: Kotlin is a statically typed language, which means that the type of variables cannot change at runtime.
• Null Safety: The type system of Kotlin eliminates the danger of null references in code.
• Concise: Kotlin reduces the amount of boilerplate code that is needed.
• Interoperable: Kotlin is fully interoperable with the Java programming language.
• Tool-Friendly: Kotlin works with all major Java tools and frameworks.
• Pragmatic: Kotlin focuses on solving problems that developers face in their daily work.

History of Kotlin

Kotlin is a modern programming language primarily designed for the Java Virtual Machine (JVM) and Android development. Here is a brief history of Kotlin with important dates:

• July 2011: JetBrains, a software development company based in Russia, started the development of Kotlin.
• February 2012: The first preview of Kotlin was released to the public.
• July 2011 – February 2016: Kotlin underwent several development milestones, with updates and improvements based on user feedback.
• February 15, 2016: JetBrains announced the first official stable release of Kotlin, Kotlin 1.0, making it available for production use.
• May 17, 2017: Google announced official support for Kotlin as a first-class language for Android app development at Google I/O. Kotlin became an officially supported language alongside Java for Android development.
• October 2017: KotlinConf, the first Kotlin-specific conference, was held in San Francisco, showcasing Kotlin’s growing popularity in the developer community.
• March 1, 2018: Kotlin 1.2 was released, introducing several new features and improvements to the language.
• October 2018: Kotlin 1.3 was released, bringing new language features and improvements, including experimental support for multiplatform projects.
• February 2020: JetBrains launched the Kotlin Foundation, an independent non-profit organization, to ensure the long-term development and support of the Kotlin programming language.
• May 2020: Google announced that 70% of the top 1,000 Android apps on the Google Play Store were using Kotlin for app development.
• February 2021: Kotlin 1.5 was released, introducing new language features and enhancements.

Where is Kotlin Used?

Kotlin is being utilized extensively in the tech domain nowadays. It is a great choice among professionals in the following domains:

Android Development– Kotlin is now the preferred language for Android development; it is fully integrated with Android Studio. 
Develop Server-Side Applications– You can employ Kotlin to develop server-side applications, web services, and microservices using frameworks like Spring Boot, Ktor, etc.
Multiplatform Projects– Kotlin can target JVM, Android, JavaScript, and Native so you can use it for building multiplatform projects.
Highly Scalable Systems– Kotlin’s specific features like null-safety, immutability, and conciseness make it a good choice for highly scalable systems.
Reactive Applications– Kotlin provides good support for reactive programming using libraries like RxKotlin and Flow.
Polyglot Projects– Kotlin works seamlessly with Java, such that you can add Kotlin files to a Java project and vice versa. So it works great for polyglot projects.

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How to Start with Kotlin?

Learning the ins and outs of Kotlin is easy, and working with it is even easier. Mentioned below are some steps to get you started with Kotlin:

1. Install Kotlin: You can install the Kotlin compiler (kotlinc) and the Kotlin IntelliJ IDEA plugin.
2. Try Kotlin in the Browser: Head over to try.kotlinlang.org and enter the code in Kotlin without installing anything. This is a great way to get a taste of the language.
3. Create your First Program: Create a Hello World program to print “Hello from Kotlin!”. For this, you can employ IntelliJ IDEA or the online editor.
4. Learn the Kotlin Syntax: Study the Kotlin language syntax, data types, operators, control flows, functions, classes, objects, etc. For this, you can take help from the Kotlin documentation.
5. Build an Android App: If you are an Android developer, build a simple Android app in Kotlin using Android Studio. This is a great way to learn Kotlin.
6. Build a Command-Line Application: A simple command-line Kotlin application can be created so as to build a tool or perform an automated task.
7. Explore Advanced Topics: Learn about advanced Kotlin concepts like coroutines, delegates, DSLs, etc. 
8. Read Books on Kotlin:  Some excellent books on Kotlin include Kotlin in Action, Kotlin Programming Cookbook, Kotlin for Beginners, and Kotlin for Android Developers.
9. Practice: The only way to learn Kotlin is to practice writing as many Kotlin codes as possible. Try to build small practice projects, read other people’s Kotlin code, and contribute to open-source Kotlin projects. Practice is the key!
10. Stay Up-to-Date: Kotlin releases updates frequently, so stay up-to-date with the latest Kotlin features and news to leverage the full power of the language.

Difference between Java vs Kotlin

Here is a comparison between Java and Kotlin in tabular form:

Kotlin Basics

Mentioned below are some basic syntax rules in Kotlin:

– Use “//” for single-line comments and “/* */” for multi-line comments.
– No semicolons are required after statements.
– Definitions are separated with a newline.
– Use “:”, not “;” for separating statements. 
– Define top-level functions, properties, and classes without specifying receivers.

Data Types

Kotlin has the following five basic data types:

– Numbers: Int, Long, Double, and Float
– Characters: Char
– Booleans: Boolean 
– Strings: String
– Null: Null

Variables

Variables in Kotlin are declared using the var keyword, as shown below:

var name: String = "John"
var age: Int = 30

You can also define variables as immutable using the val keyword, as shown below:

val name: String = "John" 
val age: Int = 30

Constants

Constants are defined using the val keyword and must be assigned a value immediately, as shown below:

val PI = 3.14 
val GREETING = "Hello"

Constants can be numbers, strings, booleans, or null data types.

Arrays

Kotlin has the following two types of arrays:

– Mutable arrays, which are declared with arrayOf as shown below:

val numbers = arrayOf(1, 2, 3)

– Immutable arrays, which are declared with listOf as shown below:

val numbers = listOf(1, 2, 3)

You can access these elements using the square bracket notation, as shown below:

val first = numbers[0]  // 1
val last = numbers[2]  // 3

Conditionals (if-else) 

Mentioned below is a representation of the if-else expression in Kotlin:

if (condition) {
    // block of code
} else { 
    // block of code
}

Moreover, the following is a representation of the else if conditional:

if (condition1) {
    // block of code
} else if (condition2) {
    // block of code
} else {
    // block of code
}

Furthermore, Kotlin has a ternary operator for single-line conditionals, which is shown below:

val result = if (condition) "Success" else "Failure"

Loops (for, while, and do-while)

Kotlin supports the following three types of loops:

- for loop
for (i in 1..10) {
    print(i)  // 1 2 3 4 5 6 7 8 9 10
}
- while loop
var i = 1 
while (i < 10) { 
    print(i) 
    i++ 
} 
- do-while loop
var i = 1  
do { 
    print(i) 
    i++ 
} while (i < 10)

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Functions

Kotlin supports default arguments, named arguments, varargs, lambda expressions, and higher-order functions.

You can define functions using the fun keyword, as shown below:

fun sayHello() {
    println("Hello!")
}

Furthermore, you can define parameters in the following manner:

fun sayHello(name: String) {
    println("Hello $name!") 
}

Moreover, a return type can be defined in the following manner:

fun sum(a: Int, b: Int): Int {
    return a + b
}

Classes 

You can define classes with the class keyword, as shown below:

class Person(val name: String) {
}

You can also have mutable properties by using var, which is shown below:

class Person(var name: String) {  
}

And methods:

class Person(var name: String) {  
   fun sayHello() {
       println("Hello, I'm $name!") 
   }
} 

Objects and Companion Objects

You can define singleton objects in Kotlin using the object declaration, as shown below:

object Singleton {
    val name = "Singleton"
    fun printMessage() { 
        println("Message from $name")
    }
}

Defining companion objects that are like singletons but are attached to a class, as shown below:

class Person {
    companion object {
        val name = "Person"
        fun printMessage() {
            println("Message from $name") 
        }
    }
}

You can access the members of objects and companion objects using the type name, as shown below:

Singleton.printMessage()  // Prints "Message from Singleton"
Person.printMessage()   // Prints "Message from Person"

Constructors

You can define constructors using the init keyword, as shown below:

class Person (val name: String) {
    init {
        println("Creating a new Person with name $name")
    }
}

You can also have a primary constructor as well as secondary constructors, as shown below:

class Person(val name: String) {
    constructor(name: String, age: Int): this(name) {
        // ... 
    }
}

Visibility Modifiers

Kotlin has the following three visibility modifiers:

– public: Can be accessed from everywhere 
– internal: Can be accessed only within the same module
– private: Can be accessed only within the same file
By default, a member has public visibility. 

Null Safety

Kotlin’s type system eliminates the danger of null references in code. You can define a variable as nullable by suffixing its type with a “?” (question mark), as shown below:

val str: String? = null 
val length = str?.length  // length is Int?, can hold null 
val nonNullLength = str?.length ?: 0 // elvis operator, length is Int

This means that you have to actively opt-in for nullability by declaring a variable/parameter nullable. Otherwise, it is assumed to be non-null.

Smart Casts

The Kotlin compiler employs smart casts to enable safe null checks. This means that after performing a null check, the variable is considered non-null in the scope below the check, as shown in the example below:

For example:

val name: String? = "John"
name != null // Smart cast to String 
println(name.length) // Prints 5 

Extensions 

You can extend the functionality of existing classes by adding extension functions and extension properties. Mentioned below is a means of defining an extension using the keyword extension:

extension String {
    fun printHello() {
        println("Hello $this")
    } 
}

You can then call the extension function on any String, as shown below:

"John".printHello() // Prints "Hello John"

Lambda Expressions

Lambda expressions allow you to define anonymous functions in a concise manner.

The basic syntax of a lambda expression is mentioned below:

{ argument -> body }

For example: 

{ println("Hello") } 

Or with an argument, as shown below:

{ name -> println("Hello $name") } 

Lambdas are useful when defining inline functions, higher-order functions, or passing a function as an argument to another function.

Standard Library

Kotlin has a very useful standard library with functions for collections, input/output, reflection, concurrency, etc.

Some examples of the functions in the standard library are mentioned below:

– listOf(), setOf(), and mapOf() to create collections 
– filter(), map(), reduce(), and other functional operators on collections
– sequence() to create lazy sequences 
– readText() and writeText() for file I/O  
– runBlocking() to run tasks concurrently 
– and much more! 

The standard library in Kotlin aims to support all common tasks to avoid the need for external libraries for everyday needs.

Conclusion

Kotlin is a modern programming language that has gained popularity among developers. It is concise with an expressive syntax, type inference, and null safety features. It is a universal language that can be used to develop various types of applications including Android, server-side, and web applications. 

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