Kotlin Coroutines Cheat Sheet

Bruno Pivoto Azevedo — Wed, 15 Oct 2025 18:54:47 +0000

⚙️ Kotlin Coroutines Cheat Sheet (For Android Devs)

I like to share content that I use during study and work.
This is a cheatsheet that I used when developing with coroutines.

Coroutines are lightweight threads used for asynchronous and concurrent programming in Kotlin.

They allow you to run tasks like network or DB operations without blocking the main thread.

🔹 Core Keywords & Builders

Keyword / Builder	Description
`suspend`	Marks a function that can be paused and resumed later
`launch`	Starts a coroutine that doesn’t return a result
`async`	Starts a coroutine that returns a `Deferred` result
`await()`	Waits for the result of an `async` coroutine
`withContext()`	Switches the coroutine context (e.g., Main, IO)
`runBlocking`	Starts a blocking coroutine (usually for testing)
`coroutineScope`	Creates a new scope that waits for all its children
`supervisorScope`	Similar to coroutineScope but failures don’t cancel siblings
`delay()`	Non-blocking sleep function
`yield()`	Yields execution to other coroutines temporarily

🔹 Dispatchers

Dispatcher	Used for
`Dispatchers.Main`	UI operations (Android main thread)
`Dispatchers.IO`	I/O tasks: networking, DB, file access
`Dispatchers.Default`	CPU-intensive work
`Dispatchers.Unconfined`	Executes in current thread (advanced use)

🔹 Example 1: Basic Launch

import kotlinx.coroutines.*

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

Output:

Hello,
World!

🔹 Example 2: async/await

import kotlinx.coroutines.*

suspend fun fetchUser(): String {
    delay(1000)
    return "Bruno"
}

suspend fun fetchPosts(): List<String> {
    delay(1000)
    return listOf("Post 1", "Post 2")
}

fun main() = runBlocking {
    val user = async { fetchUser() }
    val posts = async { fetchPosts() }
    println("User: ${user.await()}, Posts: ${posts.await()}")
}

Output:

User: Bruno, Posts: [Post 1, Post 2]

🔹 Example 3: withContext

import kotlinx.coroutines.*

suspend fun loadUserData() = withContext(Dispatchers.IO) {
    // background work
    "User data loaded"
}

fun main() = runBlocking {
    val result = loadUserData()
    println(result)
}

Output:

User data loaded

🔹 Flow basics

import kotlinx.coroutines.*
import kotlinx.coroutines.flow.*

fun numbersFlow(): Flow<Int> = flow {
    for (i in 1..3) {
        emit(i)
        delay(100)
    }
}

fun main() = runBlocking {
    numbersFlow()
        .map { it * 2 }
        .collect { println(it) }
}

Output:

2
4
6

You can try these examples yourself on Kotlin Playground.

DEV Community: Bruno Pivoto Azevedo

Kotlin Coroutines Cheat Sheet

⚙️ Kotlin Coroutines Cheat Sheet (For Android Devs)

🔹 Core Keywords & Builders

🔹 Dispatchers

🔹 Example 1: Basic Launch

Output:

🔹 Example 2: async/await

Output:

🔹 Example 3: withContext

Output:

🔹 Flow basics

Output: