Android Interview Questions with Kotlin Coroutines
1) What are Kotlin Coroutines, and how are they different from traditional threading?
Kotlin Coroutines are a language feature that simplifies asynchronous programming. Unlike traditional threading, coroutines are lightweight and don’t necessarily require a separate thread for execution. They provide a more efficient and readable way to handle asynchronous tasks.
2) Explain the difference between launch and async in Kotlin Coroutines.
Launch is used for fire-and-forget asynchronous tasks, while async is used when you need to perform a task and await its result. async returns a Deferred object, which can be used to obtain the result once the coroutine completes.
3) What is the purpose of the suspend modifier in Kotlin Coroutines?
The suspend modifier is used to mark a function or lambda expression as a coroutine. It indicates that the function can be suspended, allowing other coroutines to run while it’s waiting for a non-blocking operation to complete.
4) How can you handle errors in Kotlin Coroutines?
In coroutines, exceptions are handled using try/catch blocks. Additionally, the CoroutineExceptionHandler interface can be used to define a global handler for uncaught exceptions within a coroutine scope.
5) Explain the concept of Coroutine Context in Kotlin Coroutines?
Coroutine Context is a set of elements that define the behavior and characteristics of a coroutine. It includes things like dispatchers, exception handlers, and coroutine name. The context is used to determine how and where the coroutine will be executed.
6) What is a Coroutine Dispatcher, and how is it related to threading?
A Coroutine Dispatcher is responsible for determining the thread or threads on which the coroutine will be executed. Common dispatchers include Dispatchers.Main for UI operations and Dispatchers.IO for I/O tasks.
7) Explain the concept of Coroutine Builders in Kotlin?
Coroutine Builders are functions that are used to create and start coroutines. Examples include launch, async, and runBlocking. They provide a convenient way to initiate and control the execution of coroutines.
8) What is structured concurrency in Kotlin Coroutines?
Structured concurrency is an approach to managing coroutines that ensures the proper execution and completion of all child coroutines within a specific scope. It helps in avoiding common pitfalls associated with coroutine management.
9) How do you achieve parallelism using Kotlin Coroutines?
Parallelism in coroutines can be achieved using the async builder along with await to await the results. Multiple asynchronous tasks can be started concurrently, and their results can be combined when needed.
10) Explain the concept of Coroutine Flow in Kotlin?
Coroutine Flow is a type of cold asynchronous stream that can emit multiple values over time. It’s used for handling asynchronous sequences of data, providing a reactive programming style within the coroutine context.
11) What is the purpose of the CoroutineScope in Kotlin Coroutines?
`CoroutineScope` is a way to define the scope of a coroutine. It provides a structured way to launch coroutines and ensures that they are properly cancelled when the scope is cancelled.
12) Explain the concept of coroutine cancellation and how it differs from thread interruption?
Coroutine cancellation is a cooperative mechanism where a coroutine is given the opportunity to clean up resources before it is cancelled. It differs from thread interruption, which forcefully stops a thread without giving it a chance to perform cleanup.
13) What is the purpose of the GlobalScope in Kotlin Coroutines?
`GlobalScope` is a predefined coroutine scope that lasts for the entire application lifetime. While it can be convenient, it’s generally recommended to use custom coroutine scopes to ensure structured concurrency.
14) How do you test code that involves Kotlin Coroutines?
Testing coroutine code can be done using libraries like `kotlinx-coroutines-test`, which provides utilities for testing suspending functions and coroutines in a controlled environment. You can use `TestCoroutineDispatcher` to control the execution of coroutines.
15) Explain the concept of coroutine channels in Kotlin?
Coroutine channels provide a way for coroutines to communicate with each other by sending and receiving elements. They offer a convenient way to implement producer-consumer patterns and facilitate the flow of data between coroutines.
16) Explain withContext in Coroutines?
withContext does not create a new coroutine, it only shifts the context of the existing coroutine and it’s a suspend function whereas launch and async create a new coroutine and they are not suspend functions.
This is particularly useful for changing the Dispatcher of the Coroutines, which controls the thread the Coroutines run on.
So, withContext is a suspend function through which we can do a task by providing the Dispatcher on which we want the task to be done.
16) Explain Dispatchers in Kotlin Coroutines?
Dispatchers help Coroutines in deciding the thread on which the task has to be done. We use Coroutines to perform certain tasks efficiently. Coroutines run the task on a particular thread. This is where the Dispatchers come into play. Coroutines take the help of Dispatchers in deciding the thread on which the task has to be done.
Dispatchers in Kotlin Coroutines are like Schedulers in RxJava.
Very frequently we use the following Dispatchers in our Android project:
- Dispatchers.Default
- Dispatchers.IO
- Dispatchers.Main
However, when we go through the documentation, we have one more:
- Dispatchers.Unconfined
So, there are 4 types of Dispatchers in Kotlin Coroutines:
- Dispatchers.Default
- Dispatchers.IO
- Dispatchers.Main
- Dispatchers.Unconfined
Dispatchers.Default
We should use Dispatchers.Default to perform CPU-intensive tasks.
Example use cases:
- Doing heavy calculations like Matrix multiplications.
- Doing any operations on a bigger list present in the memory like sorting, filtering, searching, etc.
- Applying the filter on the Bitmap present in the memory, NOT by reading the image file present on the disk.
- Parsing the JSON available in the memory, NOT by reading the JSON file present on the disk.
- Scaling the bitmap already present in the memory, NOT by reading the image file present on the disk.
- Any operations on the bitmap that are already present in the memory, NOT by reading the image file present on the disk.
So, now we know where we can use the Dispatchers.Default.
We can think of Dispatchers.Default as a Schedulers.computation() of RxJava.
launch(Dispatchers.Default) {
// Your CPU-intensive task
}Dispatchers.IO
We should use Dispatchers.IO to perform disk or network I/O-related tasks.
Example use cases:
- Any network operations like making a network call.
- Downloading a file from the server.
- Moving a file from one location to another on disk.
- Reading from a file.
- Writing to a file.
- Making a database query.
- Loading the Shared Preferences.
So, now we know where we can use the Dispatchers.IO.
In a nutshell, anything related to file systems or networking should be done using Dispatchers.IO as those tasks are IO-related tasks.
We can think of Dispatchers.IO as a Schedulers.io() of RxJava.
launch(Dispatchers.IO) {
// Your IO related task
}Dispatchers.Main
We should use Dispatchers.Main to run a coroutine on the main thread of Android. We all know where we use the main thread of Android. Mainly at the places where we interact with the UI and perform small tasks.
Example use cases:
- Performing UI-related tasks.
- Any small tasks like any operations on a smaller list present in the memory like sorting, filtering, searching, etc.
So, now we know where we can use the Dispatchers.Main.
We can think of Dispatchers.Main as a AndroidSchedulers.mainThread() of RxAndroid(RxJava bindings for Android).
launch(Dispatchers.Main) {
// Your main thread related task
}Dispatchers.Unconfined
As per the official documentation: A coroutine dispatcher that is not confined to any specific thread. It executes the initial continuation of a coroutine in the current call frame and lets the coroutine resume in whatever thread that is used by the corresponding suspending function, without mandating any specific threading policy.
It does not change the thread. When it is started, it runs on the thread on which it was started. If it is resumed, it runs on the thread that resumed it.
If I put it simply: We should use Dispatchers.Unconfined when we do not care where the coroutine will be executed.
launch(Dispatchers.Unconfined) {
// Your task for which you do not care about the thread on which it should run.
}Thank you for reading. 🙌🙏✌.
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