Android App Development Interview Questions for 3 Years Experience
40 questions with answers for candidates with 3 years of experience — 3 easy, 31 medium, 6 hard.
What interviewers expect: 3 years experience
Three years of experience means interviewers expect solid architecture skills and some ownership of quality. Expect mobile system design for a feature like a feed or chat, performance questions on ANRs and memory leaks, and Compose optimisation. You should explain trade-offs between approaches and show examples where you improved a metric like crash rate or startup time.
This set is weighted towards Testing, Performance and Play Store (7), Jetpack Compose (7), Coroutines and Flow (6), Networking and APIs (5).
Mobile feature system design Performance and memory profiling Compose stability and optimisation CI and release processes
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01
A payment SDK integration fails only in release builds. What would you check?
First check R8 or ProGuard: release builds shrink and obfuscate code, and the SDK may need keep rules for classes used by reflection or JSON parsing. Check the SDK documentation for required rules and add them to proguard-rules.pro. Also verify the release signing key SHA is registered with the provider, the correct production keys and base URLs are used, and network security config allows the domains.
02
Your team is migrating a Java Android app to Kotlin. How would you plan it?
Kotlin and Java interoperate, so migrate gradually rather than all at once. Start with new features in Kotlin, then convert leaf classes like models and utilities, writing tests before converting. Add nullability annotations to Java code so Kotlin sees correct types. Review auto-converted code because it often overuses !!. Track progress per module and agree on style rules with ktlint or detekt so the codebase stays consistent.
03
Compare kotlinx.serialization, Moshi and Gson for JSON parsing.
kotlinx.serialization is Kotlin-first, uses a compiler plugin with no reflection, respects default values and nullability, and works in Kotlin Multiplatform. Moshi supports Kotlin through codegen and is also reliable. Gson uses reflection, ignores Kotlin nullability and default values, and can put null into non-null fields, causing crashes later; it is in maintenance mode. For new Android projects, kotlinx.serialization is the common choice.
04
Write a function that retries a suspend call with exponential backoff.
Read the rejection email and policy centre message carefully to see which permission or declaration failed, often SMS, call log, background location, all-files access or exact alarms. Remove the permission if a less sensitive alternative exists, such as the SMS Retriever API or photo picker. Otherwise update the permission declaration form with a clear use case and video. Check the merged manifest for permissions added by libraries.
06
What is CompositionLocal and when should you use it?
CompositionLocal passes data implicitly down the tree without threading it through every parameter, like LocalContext, LocalDensity or MaterialTheme values. Create one with compositionLocalOf when values change often, or staticCompositionLocalOf when they rarely change. Use it for cross-cutting values like theme or analytics loggers, not for regular screen data, because implicit dependencies make composables harder to understand and test.
07
How does coroutine cancellation work, and why must code be cooperative?
Cancelling a Job sets it to cancelling state, and the next suspension point such as delay, withContext or a suspending library call throws CancellationException. A tight CPU loop with no suspension keeps running, so check isActive or call ensureActive() or yield() inside it. Do not swallow CancellationException in a generic catch block; rethrow it. Use finally or withContext(NonCancellable) for cleanup that must finish.
08
Tell me about a time a bug you introduced reached production. How did you handle it?
Situation: a migration I wrote missed a default value, and some users lost their saved addresses. Task: fix it and regain trust. Action: I told my lead immediately, we paused the rollout, I wrote a correct migration with a test covering upgrades from the last three versions, and we restored data from the server for affected users. Result: impact stayed small, and migration tests became mandatory in our CI.
On every pull request, run lint, ktlint or detekt, unit tests and a debug build in a CI service like GitHub Actions or Bitrise, with Gradle caching. On merge to main, build a signed release AAB using secrets, run instrumented tests on emulators or a device farm, and upload to the Play internal track with Gradle Play Publisher or fastlane. Promote to production manually after QA with a staged rollout.
10
How do LazyColumn keys improve performance and correctness?
By default, items are identified by position, so inserting or deleting an item can make Compose reuse state for the wrong item and recompose more than needed. Supplying key = { it.id } gives each item a stable identity, so remembered state, animations with animateItem and scroll position follow the right item. Also supply contentType for mixed lists so compositions are reused efficiently. Keys must be unique and Bundle-saveable.
11
How do you handle a code review comment you disagree with?
I first assume the reviewer has a reason and ask questions to understand it. If I still disagree, I explain my reasoning with evidence, such as documentation, a benchmark or a test, and suggest a short call if comments go back and forth. If it is a matter of preference, I follow the team convention. The goal is the best code for the team, not winning the argument.
12
What is a BroadcastReceiver and what limits apply since Android 8?
A BroadcastReceiver responds to broadcast intents. Since Android 8, most implicit broadcasts cannot be received by receivers declared in the manifest; you register them at runtime with registerReceiver while the app is running. A few exemptions exist, like BOOT_COMPLETED and locale change. Since Android 14, runtime receivers must specify RECEIVER_EXPORTED or RECEIVER_NOT_EXPORTED. onReceive runs on the main thread, so keep it short or use goAsync.
13
The app shows an ANR when the user taps Save. The save function is suspend. What could be wrong?
A suspend function does not automatically run off the main thread. If it calls blocking code, like a synchronous file write, a SharedPreferences commit, a blocking SDK or heavy JSON parsing, it still blocks the main thread. Check with a profiler or StrictMode. Fix by wrapping the blocking part in withContext(Dispatchers.IO) or Default, or by using main-safe APIs such as Room suspend DAOs or DataStore.
14
Write a use case that combines cart items and a coupon into a final total.
Use lifecycleScope.launch with repeatOnLifecycle(Lifecycle.State.STARTED) so collection starts when the UI is visible and stops in the background, avoiding wasted work and crashes from updating views that are not ready. In a Fragment, use viewLifecycleOwner.lifecycleScope because the fragment view can be destroyed while the fragment lives. In Compose, use collectAsStateWithLifecycle(), which does the same lifecycle-aware collection.
16
Write a periodic sync job with WorkManager that runs only on unmetered network.
Interfaces let us swap implementations, mainly fakes in tests and alternate data sources, and they define clear contracts between modules so feature modules depend on abstractions instead of concrete network code. But the rule is not absolute: if a class has one implementation and is easy to test directly, an interface adds noise. I would explain the reason with an example test and our team convention.
18
What is the difference between List and MutableList, and is List truly immutable?
List is a read-only interface exposing only reading operations, while MutableList adds add, remove and set. A List is not guaranteed immutable: the underlying object might be an ArrayList that another reference can still modify. For real immutability use kotlinx.collections.immutable or create defensive copies. In ViewModels, expose List or StateFlow<List> publicly and keep the mutable version private to protect state.
19
A Compose list scrolls with jank on low-end phones. How do you investigate and fix it?
Test a release build with R8, since debug builds are much slower. Use Layout Inspector recomposition counts and a system trace or Macrobenchmark to find hot spots. Common fixes: add keys and contentType, avoid heavy work or sorting inside composables, move computation to the ViewModel, use derivedStateOf for scroll-based state, defer state reads with lambda modifiers like offset { }, load images at the right size with Coil, and add a Baseline Profile.
20
Write code to request camera permission using the Activity Result API.
Analyse the build with APK Analyzer. Publish as an App Bundle so users get only their density, language and ABI. Enable R8 and resource shrinking, convert images to WebP or vectors, remove unused libraries and duplicate dependencies, and move large optional features or assets to Play Feature Delivery or Play Asset Delivery. Avoid bundling all native libraries for every ABI. Track size in CI.
22
What does derivedStateOf do and when should you use it?
derivedStateOf creates state computed from other state, and only triggers recomposition when the computed result changes. A classic example is showing a scroll-to-top button: val showButton by remember { derivedStateOf { listState.firstVisibleItemIndex > 0 } }. Without it, every scroll pixel would recompose. Do not use it when the result changes as often as the input, because it only adds overhead.
23
Users report the app loses form data when they switch to another app and come back after a while. Why?
The system killed the process to reclaim memory while the app was in the background. When the user returns, Android recreates the Activity but ViewModel data is gone because the process died. Fix it by storing small UI state in SavedStateHandle or rememberSaveable, which survive process death, and persisting drafts to Room or DataStore. Test with Don't keep activities or adb shell am kill.
24
A crash says IllegalStateException: Can not perform this action after onSaveInstanceState. What is happening?
A fragment transaction or dialog show was committed after the Activity saved its state, usually because a network callback finished while the app was in background. Committing then would lose state. Fix by triggering navigation only when the lifecycle is at least STARTED, collecting events with repeatOnLifecycle, or deferring the action. commitAllowingStateLoss hides the crash but can lose the transaction, so use it only when that is acceptable.
25
Write a Room database class with a migration that adds a column.
Situation: a designer wanted a custom tiny close icon on a full-screen dialog. Task: keep the app accessible without blocking the design. Action: I showed that the touch target was below the 48dp guideline and that TalkBack had no label, and prototyped the same look with a larger invisible touch area. Result: we kept the visual style, passed accessibility checks, and agreed to review touch targets in future design handoffs.
27
Write a search flow that debounces user input and cancels stale requests.
A use case is a class with one job, like GetDiscountedCartTotalUseCase, typically exposing operator fun invoke. It holds business logic that combines repositories or is reused by several ViewModels. It keeps ViewModels thin and logic testable. For simple apps where the ViewModel only calls one repository method, use cases add boilerplate without benefit, so the domain layer is optional in the official guidance.
29
Explain LaunchedEffect, DisposableEffect and SideEffect.
LaunchedEffect(key) launches a coroutine when it enters composition and restarts when the key changes, used for one-time loads or showing a snackbar. DisposableEffect(key) runs setup and requires an onDispose block for cleanup, used for registering listeners or lifecycle observers. SideEffect runs after every successful recomposition to publish Compose state to non-Compose code, such as analytics. Choose keys carefully so effects do not restart unexpectedly.
30
Write an OkHttp interceptor that adds a bearer token to every request.
Check Android vitals for excessive wake locks and wakeups, then use Battery Historian or the Energy Profiler to look at wake locks, alarms, location requests, jobs and network activity. Common causes are frequent location updates, a foreground service left running, polling instead of push, and WorkManager jobs scheduled too often. Fix by batching work, using lower location priority, stopping services promptly and adding proper constraints.
Use the Compose testing APIs with createComposeRule or createAndroidComposeRule. Find nodes by text, content description or testTag, then perform actions and assertions, like onNodeWithText("Login").performClick() and onNodeWithTag("error").assertIsDisplayed(). Test stateless composables with fake state for speed. Tests synchronise with Compose automatically. Screenshot testing tools like Roborazzi or Paparazzi catch visual regressions without a device.
SavedStateHandle is a key-value map available to a ViewModel that is saved into the instance state Bundle, so it survives process death as well as configuration changes. Navigation arguments are also placed in it automatically. Use it for small, essential UI state like a search query, selected filter or the ID of the item being edited. Do not put large lists in it; reload those from the repository.
34
Write a Flow that combines user settings and product list into one UI state.
targetSdkVersion tells Android which platform behaviour your app was tested against; the system applies newer behaviour changes only when you target that level. The Play Store requires new apps and updates to target a recent API level, usually within one year of a release, so users benefit from security and privacy changes. minSdk sets the oldest supported version and compileSdk the API you compile against.
36
Tell me about an app or feature you are proud of building.
Choose something with clear impact. For example: I built the offline cart for our grocery app. Users in low network areas could add items without connection, and the cart synced later with conflict handling. I used Room, WorkManager and a sync status field, and wrote migration and sync tests. After release, cart abandonment from network errors dropped noticeably, and the pattern was reused for the wishlist feature.
37
Write a delegated property that logs whenever a value changes.
import kotlin.properties.Delegates
class Settings {
var theme: String by Delegates.observable("light") { prop, old, new ->
println("${prop.name} changed from $old to $new")
}
}
// Use Delegates.vetoable if you need to reject a change
// by returning false from the lambda.
network_security_config.xml, referenced from the manifest, controls TLS behaviour without code. Since Android 9, cleartext HTTP is blocked by default; you can allow it for specific debug domains. You can trust user-added CAs only in debug builds for tools like Charles or proxies, and define certificate pins with expiry. Keeping cleartext disabled in production is an important security baseline.
39
Users who reinstall the app lose all their settings. How can you restore them?
Android Auto Backup automatically backs up app data to the user's cloud backup account for apps targeting API 23 and above, unless disabled. Configure dataExtractionRules for Android 12 and above to include settings files and exclude tokens or caches. For important data like notes, sync to your own server tied to the user's account, since backup is not guaranteed. Test with adb shell bmgr commands.
40
How do you unit test a ViewModel that uses coroutines and StateFlow?
Use kotlinx-coroutines-test. Replace Dispatchers.Main with a test dispatcher using Dispatchers.setMain in a JUnit rule, run tests in runTest so delays are skipped with virtual time, and inject dispatchers into repositories instead of hardcoding Dispatchers.IO. For flows, collect values with Turbine or backgroundScope and assert the sequence, such as Loading then Success. Fake repositories make results deterministic.
Frequently asked questions
What is asked in Android App Development interviews for 3 years of experience?
Three years of experience means interviewers expect solid architecture skills and some ownership of quality. Expect mobile system design for a feature like a feed or chat, performance questions on ANRs and memory leaks, and Compose optimisation. You should explain trade-offs between approaches and show examples where you improved a metric like crash rate or startup time.
How many questions should I practise before a Android App Development interview?
Work through all 40 questions here, then the company-wise sets for the employers you are targeting. Quality matters more than count: be able to explain why each answer is right.
Which topics matter most for 3 years of experience?
Focus first on Mobile feature system design, Performance and memory profiling, Compose stability and optimisation, CI and release processes.