Kotlin Cheat Sheet

Kotlin is a modern programming language that is concise, expressive, and interoperable with Java. Here’s a Kotlin cheat sheet covering some basic syntax and common features:

Hello World

Hello World:

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

Variables and Data Types

Variable Declaration:

val age: Int = 25
var name: String = "John"

Type Inference:

val pi = 3.14 // Type inferred as Double

Nullable Types:

var nullableName: String? = null

Functions

Function Definition:

fun add(x: Int, y: Int): Int {
    return x + y
}

Single-Expression Function:

fun multiply(x: Int, y: Int) = x * y

Control Flow

If Expression:

val result = if (x > y) "x is greater" else "y is greater"

When Expression:

when (day) {
    1 -> "Monday"
    2 -> "Tuesday"
    else -> "Other day"
}

For Loop:

for (i in 1..5) {
    println(i)
}

Collections

List:

val numbers = listOf(1, 2, 3, 4, 5)

Mutable List:

val mutableNumbers = mutableListOf(1, 2, 3, 4, 5)

Map:

val user = mapOf("name" to "John", "age" to 25)

Here is a dedicated Kotlin Collections Cheat Sheet.

Classes and Objects

Class Declaration:

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

Object Declaration:

object MySingleton {
    // Singleton object
}

Extension Functions:

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

val greeting = "Hello".addExclamation()

Null Safety

Safe Call Operator:

val length: Int? = name?.length

Elvis Operator:

val length = name?.length ?: 0

Coroutines

Simple Coroutine:

suspend fun fetchData() {
    // Coroutine logic
}

Launch Coroutine:

GlobalScope.launch {
    fetchData()
}

Here is a dedicated Kotlin Coroutines Cheat Sheet.

Android Development (Sample)

Android TextView Initialization:

val textView = findViewById<TextView>(R.id.textView)
textView.text = "Hello, Kotlin!"

Notes

• Kotlin is interoperable with Java, making it suitable for Android development.
• It introduces features like null safety, extension functions, and coroutines.

This Kotlin cheat sheet covers some basic syntax and features. Kotlin has a rich set of features, so refer to the official Kotlin documentation for more in-depth learning.