20 Kotlin Coroutines Interview Questions and Answers

Coroutines are a powerful tool for concurrent and parallel programming in Kotlin. They can help you write code that is more efficient and easier to read and maintain. If you are applying for a position that involves Kotlin development, it is likely that you will be asked questions about coroutines during your interview. In this article, we review some of the most common Kotlin coroutines interview questions and provide example answers to help you prepare.

Kotlin Coroutines Interview Questions and Answers

Here are 20 commonly asked Kotlin Coroutines interview questions and answers to prepare you for your interview:

1. What are coroutines?

Coroutines are a type of light-weight thread that can be used to improve the performance of concurrent code. Coroutines can be used to suspend and resume execution of code blocks, which can help to avoid the overhead of creating and destroying threads.

2. Can you explain the difference between a thread and a coroutine?

A thread is a unit of execution that can run independently from other threads. A coroutine is a light-weight thread that can be suspended and resumed.

3. How do threads compare with coroutines in terms of performance?

Threads are typically heavier than coroutines, so they can be more expensive in terms of performance. However, this is not always the case, and it really depends on the specific implementation. In general, coroutines tend to be more efficient when it comes to CPU usage, but threads may be better when it comes to I/O bound tasks.

4. Does Kotlin have any built-in support for concurrency? If yes, then what is it?

Yes, Kotlin has built-in support for concurrency via coroutines. Coroutines are light-weight threads that can be used to improve the performance of concurrent code.

5. Why are coroutines important?

Coroutines are important because they allow you to write asynchronous code that is more readable and easier to reason about than traditional asynchronous code. Coroutines also have the ability to suspend and resume execution, which can make your code more efficient.

6. What makes coroutines more efficient than threads?

Coroutines are more efficient than threads because they are lightweight and can be suspended and resumed without incurring the overhead of a context switch. This means that they can be used to perform tasks that would otherwise block a thread, without incurring the same performance penalty.

7. Can you explain what suspend functions are?

Suspend functions are functions that can be paused and resumed at a later time. This is useful for long-running tasks that might need to be interrupted, such as network requests. By using suspend functions, you can ensure that your code is more responsive and can avoid potential errors.

8. Are suspend functions executed by default on the main thread or some other one?

By default, suspend functions are executed on a background thread.

9. Is it possible to use coroutines outside Android development? If yes, then how?

Yes, it is possible to use coroutines outside of Android development. One way to do this is by using the kotlinx-coroutines-core library. This library provides support for coroutines on multiple platforms, including the JVM, JavaScript, and Native.

10. What’s the difference between asynchronous code and concurrent code?

Asynchronous code is code that can run in the background without blocking the main thread. Concurrent code is code that can run in parallel with other code.

11. What happens if we call a suspend function from another suspend function?

When we call a suspend function from another suspend function, the first function will suspend execution until the second function completes. This can be used to our advantage to create asynchronous code that is easy to read and debug.

12. Can you give me an example of when you would want to run two tasks concurrently instead of sequentially?

There are a few reasons you might want to run two tasks concurrently instead of sequentially. One reason is if the tasks are independent of each other and can be run in parallel. Another reason is if one task is dependent on the other task and you want to avoid blocking the main thread. Finally, if you have a limited number of resources available, you might want to run tasks concurrently in order to make better use of those resources.

13. What is the difference between launch() and async()? Which should be used in certain situations?

The main difference between launch() and async() is that launch() will create a new coroutine and start it immediately, while async() will create a new coroutine but will not start it until something calls await() on the resulting Deferred object. In general, launch() should be used when you want a coroutine to run in the background without blocking the main thread, while async() should be used when you need to wait for the result of a coroutine before continuing.

14. What is the best way to cancel a running job in Kotlin?

The best way to cancel a running job in Kotlin is to use the cancel() function. This function will cancel the job and any associated children jobs.

15. What do you understand about Job objects? How are they different from CoroutineScope?

Job objects are the basic building blocks of coroutines. They define a coroutine’s lifecycle and provide a way to cancel it. CoroutineScope is used to define a scope for a coroutine, which determines its lifetime and other properties.

16. What happens if there’s an exception thrown inside a coroutine?

If there’s an exception thrown inside a coroutine, then the coroutine will be cancelled. All the coroutine’s children will also be cancelled, and any pending work in those coroutines will be lost.

17. What does the {Dispatchers.Main} expression mean?

The {Dispatchers.Main} expression is used to specify that a particular coroutine should run on the main thread. This is important because some operations can only be performed on the main thread, and so specifying that a coroutine should run on the main thread ensures that it will be able to perform those operations.

18. What are some common mistakes made when working with coroutines in Kotlin?

One common mistake is not using the right context when launching a coroutine. This can lead to your coroutine being cancelled when it shouldn’t be, or not being able to access the data it needs. Another mistake is not using a structured concurrency approach, which can lead to race conditions and other issues. Finally, not using the right tools for debugging can make it difficult to find and fix problems with your coroutines.

19. What are some good practices to follow when using Kotlin coroutines?

Some good practices to follow when using Kotlin coroutines include:

– Use coroutines for short-lived background tasks
– Use coroutines for tasks that can be executed in parallel
– Use coroutines for tasks that need to be executed on a different thread than the UI thread
– Do not use coroutines for tasks that need to be executed on the UI thread
– Do not use coroutines for tasks that need to be executed synchronously

20. What is your opinion on the future of coroutines in Kotlin?

I believe that coroutines will continue to be a popular feature of Kotlin, as they offer a convenient and efficient way to manage concurrency. Additionally, the Kotlin team has been very supportive of coroutines and is constantly working to improve the experience of using them.