Android Engineer Interview Questions

• What is the difference between const val and val?
• What is so interesting about data class?
• Is singleton thread-safe? vs Object?
• What are different type of scope modifiers?
• What are different Coroutine Scope?
• How to manage series and parallel execution?
• Difference between Flow/SharedFlow/StateFlow and elaborate it.
• What happens if we call .cancel() from a coroutine scope?
• What is the difference between Launch and Async in Kotlin Coroutines?

• How does Garbage collection works?
• What is a dangling pointer?
• Elaborate Memory Leak?
• Explain fragment Lifecycle when it comes to ViewPager and sliding between different fragments.
• Difference between FragmentStateAdapter and FragmentStatePagerAdapter.
• Difference between Serializable and Parcelable? What are the disadvantages of Serializable?
• How you could implement observable SharedPrefs or observable Databases i.e. Observe a certain key/table/query?
• How does layout inflation work from xml tags to view reference in memory?
• What is a Thread, Handler, Looper and Message Queue?
• What are the different methods of concurrency on Android? Can you explain the difference between ExecutorService vs CachedThreadPool vs FixedThreadPool vs AsyncTasks vs HandlerThreads?
• How does ViewModel instance provided to Activity and Fragment. How does ViewModelProviderStore decide when to retain the instance?
• How do you inspect and solve Jank issue? here
• What are the different tools available in Android development? Explain their functions?
• List the various storages that are provided by Android.
• What are the different software components of Android Jetpack?

• How to keep a video maintain playing state when we rotate screen?
• How many callbacks in Fragmnets?
• What could be the reasons when onPause didn't get triggered?
• What kind of events trigger onPause() to run?
• In what scenario does the "onDestory" get called directly after "onCreate"?
• Which callback gets called on Activity when an AlertDialog is shown?
• What's the lifecycle in PIP (Picture-in-Picture)?
• What happens if you rotate the device?
• Inside a viewpager (Fragment state pager adapter) what will be the lifecycle of the fragments when you swap from tab to another ?
• Why onActivityCreated is now depreciated in Fragment?
• Which callback should i use if i want to know when my activity came to foreground?
• When is onActivityResult called?
• What does setRetainInstance do and how you can avoid it?
• What callbacks trigger when a Dialog opens up? Conside both case, dialog attached from same activity/fragment and other activity/fragment.
• What does launchWhenCreated, launchWhenStarted, and launchWhenResumed functions do?
• What are ‘activities’? Describe the lifecycle of an activity.

• What is the role of OkHttp and Retrofit?
• What design pattern does Retrofit use?
• How would optimise handling of access token expiration? How would you handle retry network call when the api fails? (Custom Interceptor response)

• What are the problems around security when dealing with WebView.

• Provides vs binds
• Subcomponent vs component dependency, what is the difference under the hood
• What is subcomponent and what is the use? How do you use qualifiers or how would you provide different instances of a class with the same data type? Constructor Injection V/s Method Injection? What is the scope? Singleton Annotation?
• What is Circular dependency in dagger?, and how to resolve it
• What's interesting about Hilt?
• Did you use Koin? What are your thoughts on it?

• How to launch coroutine from a composable function? - LaunchedEffect
• How to launch coroutine from a non-composable function, but tied to composition? - rememberCoroutineScope()
• What is recomposition? Recomposition
• Why and when to use remember {}?
• Difference between LazyColumn and RecyclerView?
• What is AndroidView in compose?
• What is the lifecycle of composeables? Lifecycle
• How to avoid recomposition of any composable, if the state is not changed? Smart Recomposition
• What are stable types which can skip recomposition?
• What is State?
• What is MutableState and how does recomposition happens?
• How to retain State accross recomposition and configuration changes?
• Difference between Stateless and Statefull composeables?
• What are your thoughts on flat heirarchy, constraint Layout in compose vs the older view heirarchy in xml
• Difference b/w remember and LaunchedEffect
• Does re-composition of ComposeItem1 bring any affect on ComposeItem2? If yes, then how?
  • ComposeParent() { ComposeItem1 {} ComposeItem2() {...} }

• Design Image Loading Library
• Design Image Downloading Library
• Design LRU Cache
• Design a real-time Twitter feed timeline. How will you structure the backend? Will you use WebSocket or REST for this use case? Justify.

• String vs StringBuilder
• == vs .equals?
• === vs ==?

What interesting questions you had faced while giving interview for Android Engineer role (any level)? Let's open a PR.