Kotlin

Introduction to Kotlin
Kotlin is a modern, statically-typed programming language developed by JetBrains, the creators of IntelliJ IDEA and other popular IDEs. Kotlin is an open source, cross-platform language designed to be interoperable with Java, and can be compiled both to Java bytecode and JavaScript. It is fully supported on the JVM, Android, JavaScript and Native. Kotlin is a statically typed language that bridges the gap between developers and consumers. It makes sense for both backend and mobile application development. Kotlin code is more readable and understandable especially if you are new to programming. It also provides many more features to the already existing Java language.
History
Kotlin was first announced publicly in 2011, and officially released in 2016. The release of Kotlin 1.0 coincided with the release of IntelliJ IDEA 2017.2. In 2019, at the Google I/O conference, Google announced official support for Kotlin on Android.
Features
Kotlin has some appealing features, such as:
- Null safety – Kotlin offers null safety feature through type interface. This feature helps developers to detect errors at compile time and prevent unexpected NPEs at runtime.
- Extension functions – Kotlin allows developers to extend classes with new methods without having to inherit from them.
- Data classes – A class that holds data and supports basic operations such as toString(), equals(), hashCode(), etc.
- Coroutines – Coroutines allow code to be written in an asynchronous and non-blocking manner.
- DSL support – Domain Specific Languages (DSLs) are a powerful way to create external languages which are easy to use.
- Sealed classes – Sealed classes allow developers to limit the type of objects that can be created from a certain class.
Examples of Usage
Kotlin is used for writing both Android apps and server-side applications. Companies such as Airbnb, Uber, Evernote, Pinterest, and Coursera have adopted the language for their projects. Kotlin can be used for developing server-side applications and REST APIs. To do that, developers will often use Spring Boot with Kotlin. Spring Boot allows developers to build high-performance web applications, serve resources, and connect to databases. Kotlin is also being used to develop cross-platform mobile applications. It can be used with many different frameworks, including React Native, Flutter, and Cordova. Kotlin can be used to develop desktop applications. It’s possible to use Swing, JavaFX, and GTK+ to create graphical user interfaces.
Code Examples
Hello World
The following code example prints out “Hello World!”
fun main() {
println("Hello World!")
}
Extension Function
The following code example shows a custom extension function for the String class:
fun String.reverse(): String {
return this.reversed()
}
The reverse() function can then be called on any String object:
"Hello World".reverse() // Output: dlroW olleH
Data Class
The following code example shows a data class for a Person:
data class Person(val name: String, val age: Int)
The data class comes with built-in functions such as toString(), equals(), hashCode(), copy(), etc.
Kotlin has a concise and intuitive syntax, and is easy to learn, even for developers who are new to the language. Below is an example of a simple “Hello World” program written in Kotlin.
fun main() {
println("Hello World!")
}
The above program will print the string “Hello World!” to the console.
Kotlin is versatile, and can be used to write code for various scenarios. The following example illustrates the use of Kotlin to create a function that calculates the sum of two numbers:
fun sum(a: Int, b: Int): Int {
return a + b
}
The sum()
function takes two arguments, which are both of type Int
. The function then calculates and returns the sum of the arguments.
Kotlin can be used to create mobile applications, web applications, and even desktop applications. One of the most popular examples of a mobile application written in Kotlin is the popular game Candy Crush Saga. Other popular applications written in Kotlin include Google Ads, Coursera, and Trello.
Kotlin is also increasingly being used for server-side application development. Companies such as Airbnb, Uber, and Square are already using Kotlin for their backend services. It’s also possible to use Kotlin to develop Android applications. Google has released an official Kotlin API and many popular Android apps, such as Twitter and Slack, are written in Kotlin.
Code Examples
Hello World
The following is a simple “Hello World” program written in Kotlin:
fun main(args : Array<String>) {
println("Hello World!")
}
This program prints out the text “Hello World!” when run.
Fibonacci Sequence
The following code generates the first 20 numbers in the Fibonacci sequence:
fun fibonacci( n : Int ) : Int {
if ( n == 0 ) return 0
if ( n == 1 ) return 1
return fibonacci( n - 1 ) + fibonacci( n - 2 )
}
fun main( args : Array<String> ) {
for ( i in 0..19 )
println("$i ${fibonacci(i)}")
}
This program outputs the following result:
0 0
1 1
2 1
3 2
4 3
5 5
6 8
7 13
8 21
9 34
10 55
11 89
12 144
13 233
14 377
15 610
16 987
17 1597
18 2584
19 4181
JSON Parser
The following code parses a simple JSON string into a Kotlin object:
import kotlinx.serialization.json.*
val json = ""“ {
"name" : "John Doe",
"age" : 30
} ""”
val obj = Json.parse(json)
println(obj["name"]) // prints "John Doe"
println(obj["age"]) // prints 30
Network Request
The following code makes a simple GET request to a server using the ktor library:
import io.ktor.client.*
import io.ktor.client.request.*
suspend fun main() {
val client = HttpClient()
val response = client.get<String>("https://example.com/api")
println(response)
}
This program will print out the server’s response.
fun main() {
println("Hello World!")
}
The following is an example of how to create a basic class in Kotlin:
class Person {
var name: String? = null
var age: Int = 0
fun sayHello() {
println("Hello $name")
}
}
Finally, the following is an example of how to use the data class feature in Kotlin:
data class Person(val firstName: String, val lastName: String)
fun main() {
val person1 = Person("John", "Doe")
val person2 = Person("John", "Doe")
// The two objects are equal
println(person1 == person2)
}
Conclusion
Kotlin is a modern programming language that offers many features that make it well suited for developing software. It offers a concise syntax, support for both functional programming and object-oriented design principles, and built-in safety features such as null safety and immutability. Additionally, it is fully interoperable with Java and seamlessly integrates with existing Java applications.