Kotlin Programming Basics

Introduction to Kotlin

Kotlin is a modern programming language that makes developers happier. It's concise, safe, interoperable with Java, and provides many features that help you avoid common programming errors.

Key Features of Kotlin

• Null Safety
• Extension Functions
• Data Classes
• Coroutines for asynchronous programming
• Higher-Order Functions

Basic Syntax

Let's look at some basic Kotlin syntax:

// Variables
val readOnly = "I can't be changed" // Val is immutable
var mutable = "I can be changed"     // Var is mutable

// Functions
fun sayHello(name: String): String {
    return "Hello, $name!"
}

// Single-expression functions
fun double(x: Int) = x * 2

// Null safety
var nullable: String? = null
val length = nullable?.length ?: 0

// When expression (switch-case replacement)
when (x) {
    1 -> print("x is 1")
    2 -> print("x is 2")
    else -> print("x is neither 1 nor 2")
}
      

Classes and Objects

Kotlin makes creating classes and objects simple:

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

// Data class
data class User(val name: String, val email: String)

// Singleton
object DatabaseConnection {
    fun connect() = println("Connected to database")
}

// Companion object (similar to static methods)
class MyClass {
    companion object {
        fun create(): MyClass = MyClass()
    }
}
      

Extension Functions

One of Kotlin's most powerful features is the ability to extend existing classes:

fun String.addExclamation(): String {
    return this + "!"
}

val message = "Hello".addExclamation() // Returns "Hello!"
      

Coroutines

Kotlin's approach to asynchronous programming:

import kotlinx.coroutines.*

fun main() = runBlocking {
    launch {
        delay(1000L)
        println("World!")
    }
    println("Hello")
}