Async coroutine builder in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the async coroutine builder in Kotlin?

The async builder starts a coroutine that runs concurrently and returns a Deferred object, which represents a future result that can be awaited.

beginner

How do you get the result from an async coroutine?

You call the await() function on the Deferred object returned by async. This suspends the coroutine until the result is ready.

intermediate

What is the difference between launch and async coroutine builders?

launch starts a coroutine that does not return a result and is used for jobs. async starts a coroutine that returns a result wrapped in a Deferred.

intermediate

Can you explain what happens if you call await() on a Deferred that is not yet completed?

The coroutine calling await() suspends and waits until the Deferred completes and the result is available.

beginner

Show a simple Kotlin code snippet using async to run two tasks concurrently and get their results.

import kotlinx.coroutines.*

fun main() = runBlocking {
    val deferred1 = async { 10 * 2 }
    val deferred2 = async { 5 + 5 }
    println("Result 1: ${deferred1.await()}")
    println("Result 2: ${deferred2.await()}")
}

What does the async coroutine builder return?

A A Deferred object representing a future result

B A Job object with no result

C A regular function result immediately

D A Thread object

async returns a Deferred which holds a future result that can be awaited.

Which function do you call to get the result from an async coroutine?

A start()

B join()

C await()

D run()

await() suspends until the Deferred completes and returns the result.

What happens if you call await() on a Deferred that is already completed?

A Throws an exception

B Returns the result immediately without suspension

C Suspends indefinitely

D Starts the coroutine again

If the Deferred is completed, await() returns the result immediately.

Which coroutine builder is best when you want to start a coroutine that does not return a result?

A withContext

B async

C runBlocking

D launch

launch is used for coroutines that do not return a result.

What is the main advantage of using async over sequential code?

A Runs tasks concurrently to save time

B Runs tasks sequentially to avoid errors

C Blocks the main thread

D Runs tasks on a new thread always

async allows running multiple tasks at the same time, improving efficiency.

Explain how the async coroutine builder works and how you retrieve its result.

Think about how you ask a friend to do a task and wait for their answer later.

Describe the difference between launch and async coroutine builders in Kotlin.

One is for jobs without results, the other for tasks that produce results.