Launch coroutine builder in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

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

The launch coroutine builder starts a new coroutine without blocking the current thread. It runs concurrently and returns a Job that can be used to manage the coroutine's lifecycle.

intermediate

How does launch differ from async in Kotlin coroutines?

launch starts a coroutine that does not return a result and returns a Job. async starts a coroutine that returns a result wrapped in a Deferred, which can be awaited.

beginner

What does the Job returned by launch allow you to do?

The Job lets you cancel the coroutine, check if it is active or completed, and join to wait for its completion.

beginner

Write a simple Kotlin code snippet using launch to print "Hello from coroutine!".

import kotlinx.coroutines.*

fun main() = runBlocking {
    launch {
        println("Hello from coroutine!")
    }
}

intermediate

What happens if you call launch inside runBlocking?

The launch coroutine starts concurrently inside the runBlocking scope. The runBlocking waits for all its child coroutines, including the launched one, to complete before finishing.

What does the launch coroutine builder return?

A A Job

B A Deferred

C A Thread

D A Future

launch returns a Job which represents the coroutine's lifecycle.

Which of the following is true about launch?

A It blocks the current thread until completion

B It returns a result directly

C It can only be used in main thread

D It starts a coroutine that runs concurrently

launch starts a coroutine that runs concurrently without blocking the current thread.

How can you cancel a coroutine started with launch?

A By interrupting the thread

B By calling <code>stop()</code> on the coroutine

C By calling <code>cancel()</code> on the Job returned by <code>launch</code>

D By calling <code>await()</code>

The Job returned by launch has a cancel() method to stop the coroutine.

Which coroutine builder should you use if you want a result from the coroutine?

A launch

B async

C runBlocking

D delay

async returns a Deferred which holds the result of the coroutine.

What is the typical use case for launch?

A To perform background work without returning a result

B To compute a value asynchronously

C To block the main thread

D To create a new thread

launch is used for fire-and-forget background tasks that do not return a value.

Explain how the launch coroutine builder works and when you would use it.

Think about starting a task that runs alongside your main program.

Describe the difference between launch and async coroutine builders.

One is for fire-and-forget, the other for getting a value.