Android interview questions and answers

1. Kotlin data class equality

What does this Kotlin code print?

data class User(val id: Int, val name: String)
val a = User(1, "Ana")
val b = User(1, "Ana")
println(a == b)
println(a === b)

1. A.true then false
2. B.true then true
3. C.false then false
4. D.false then true

2. Sharing text to any app

On Android, you want to let the user share a piece of text using any app they choose, such as WhatsApp or Gmail. What do you use?

1. A.An explicit Intent for each popular app, such as WhatsApp and Gmail, tried one after another until one starts
2. B.A BroadcastReceiver registered in the manifest
3. C.An implicit Intent with ACTION_SEND, shown with Intent.createChooser
4. D.A ContentProvider that other apps can query

3. Dart null-aware operators

What does this Dart code print?

String? name;
print(name ?? 'Guest');
print(name?.length);

1. A.Guest, then 0
2. B.A null check error is thrown
3. C.Guest, then null
4. D.null, then null

4. What !! does on null

What happens when this line runs and token is null?

val token: String? = prefs.getString("token", null)
val length = token!!.length

1. A.length becomes 0
2. B.length becomes null
3. C.A NullPointerException is thrown
4. D.The line is skipped silently

5. What let returns

What is the type of len?

val name: String? = intent.getStringExtra("name")
val len = name?.let { it.length }

1. A.String?
2. B.Unit
3. C.Int
4. D.Int?

6. Configuring an object with apply

What does this expression return?

val paint = Paint().apply {
    color = Color.RED
    strokeWidth = 4f
    style = Paint.Style.STROKE
}

1. A.The configured Paint object
2. B.Unit, because the lambda sets properties
3. C.The last value set, Paint.Style.STROKE
4. D.A copy of a new default Paint

7. == versus === in Kotlin

For two different String objects with the same text, what do a == b and a === b return?

1. A.false and true
2. B.true and true
3. C.true and false
4. D.false and false

8. A click callback type

A composable takes a callback that receives the clicked item’s id (Int) and returns nothing. What is the parameter type?

1. A.Int -> Void
2. B.() -> Int
3. C.Function<Int>
4. D.(Int) -> Unit

9. Two suspend calls in a row

getProfile() takes 1.0 s and getOrders() takes 1.5 s. Called one after the other in the same coroutine, how long does it take?

1. A.About 1.5 s
2. B.About 2.5 s
3. C.About 1.0 s
4. D.About 0.5 s

10. Launching in GlobalScope

Why is GlobalScope.launch discouraged for loading screen data?

1. A.It runs every coroutine on the main thread only
2. B.It is not able to call any suspend functions
3. C.The work is tied to no lifecycle and can leak
4. D.It always crashes on devices with Android 14

11. Making a composable reusable

A QuantityPicker composable keeps its own count with remember. The cart screen needs to read and reset that count. What is the standard fix?

1. A.Make count a global top-level var in the file
2. B.Read the count from the composable using reflection
3. C.Hoist it: pass count in and expose an onCountChange callback
4. D.Store the count in a companion object of the screen

12. Counter jumps back to zero

The count sometimes jumps back to 0, for example when the parent screen recomposes. Why?

@Composable
fun Counter() {
    var count by mutableStateOf(0)
    Button(onClick = { count++ }) {
        Text("Count: $count")
    }
}

1. A.mutableStateOf only works inside a ViewModel class
2. B.Button onClick runs on a background thread instead
3. C.Text cannot display numbers that come from state
4. D.A new state is made each time Counter runs; use remember

13. Showing 5,000 orders

A screen shows 5,000 order rows using Column with verticalScroll and is very slow to open. What should it use?

1. A.LazyColumn, which composes only visible items
2. B.A Box with 5,000 children stacked
3. C.A Row with horizontalScroll instead
4. D.A Column inside another Column

14. Auto-incrementing IDs in Room

You want Room to assign IDs automatically for new Note rows. What do you write?

1. A.@Entity(autoId = true) on the class
2. B.@ColumnInfo(name = "auto") on the id field
3. C.@Index(unique = true) on the id field
4. D.@PrimaryKey(autoGenerate = true) val id: Long = 0

15. Room query in onCreate

A plain (non-suspend) Room DAO query is called from onCreate on the main thread. What happens by default?

1. A.The query runs and blocks the UI
2. B.Room moves it to a background thread
3. C.The query returns an empty list
4. D.Room throws an IllegalStateException

16. App Not Responding dialog

When does Android typically show an ANR for a foreground activity?

1. A.The app uses more than half of the device CPU for a while
2. B.Any single network call takes more than one second
3. C.The main thread misses an input event for about 5 seconds
4. D.The screen stays on for more than five minutes in a row

17. Sync every 5 minutes

You schedule a PeriodicWorkRequest with a 5-minute interval. What does WorkManager do?

1. A.Runs it every 5 minutes exactly
2. B.Uses the 15-minute minimum interval instead
3. C.Throws an error and never schedules it
4. D.Runs it once and then stops

18. Blocking screenshots of sensitive screens

A banking app wants to stop screenshots and screen recordings of its card details screen on Android. What does it use?

1. A.A transparent overlay drawn on the screen
2. B.The android:allowBackup flag in the manifest
3. C.A lower screen brightness while it is shown
4. D.WindowManager.LayoutParams.FLAG_SECURE on that window

19. Copying a one-time password

An app copies an OTP to the clipboard for the user. What is a good practice on modern Android?

1. A.Keep the OTP in the clipboard permanently
2. B.Copy the user's password along with the OTP
3. C.Paste the OTP into every text field automatically
4. D.Mark the clip as sensitive so previews hide it

20. viewDidLoad vs viewWillAppear

A UIKit screen should refresh its data every time the user comes back to it from a pushed screen. Where should the refresh go?

1. A.viewDidLoad() once
2. B.viewWillAppear(_:)
3. C.init(coder:) on load
4. D.loadView() override

21. remember vs rememberSaveable

In Jetpack Compose, a text field value is lost when the screen rotates. It is stored with remember { mutableStateOf("") }. What should you use instead?

1. A.derivedStateOf
2. B.LaunchedEffect
3. C.rememberSaveable { mutableStateOf("") }
4. D.A plain var outside the composable

22. Reliable background upload

An Android app must upload photos even if the user closes the app, but only on Wi-Fi. Which API should you use?

1. A.A Thread started from the Activity
2. B.WorkManager with a network-type constraint of UNMETERED
3. C.A coroutine in viewModelScope
4. D.An AlarmManager that fires every minute

23. LaunchedEffect keyed on Unit

The parent changes userId from "a" to "b" while this Profile composable stays on screen. What happens?

@Composable
fun Profile(userId: String, vm: ProfileViewModel) {
  LaunchedEffect(Unit) {
    vm.load(userId)
  }
  // ... UI
}

1. A.load("b") runs, because the composable recomposed
2. B.Nothing new loads, because an effect keyed on Unit runs only once; use LaunchedEffect(userId) so it restarts when the id changes
3. C.The app crashes with an IllegalStateException, because an effect key cannot stay the same while the parameters of its composable change
4. D.load runs twice in parallel, once for each id

24. Release build breaks JSON parsing

The debug build works, but the release build crashes or returns empty objects when parsing JSON with a reflection-based library such as Gson. What is the likely cause?

1. A.Release builds do not have the INTERNET permission
2. B.R8 renamed or removed model classes and fields; add keep rules or use a code-generating serializer like kotlinx.serialization or Moshi codegen
3. C.JSON parsing is turned off in release builds
4. D.The server detects release builds from the user agent and sends a compact JSON format with short keys, so every parsed field ends up empty

25. also compared with apply

How does also differ from apply?

1. A.also returns the lambda result; apply returns Unit
2. B.also runs on a background thread; apply does not
3. C.also gives it, apply gives this; both return the object
4. D.also only works on nullable values; apply does not

26. Snackbar shows again after rotation

A ViewModel exposes a StateFlow<String?> message. After rotation, the same Snackbar appears again. Why?

1. A.Rotation re-runs the ViewModel’s init block again
2. B.Snackbars are always shown again after rotation
3. C.collect() reads the latest value twice per frame
4. D.StateFlow hands its current value to new collectors

27. When combine first emits

You combine a user flow and a settings flow. The user flow emits at once, but settings emits after 2 seconds. When does combine first emit?

1. A.Immediately, with settings as null
2. B.Never, unless both emit at the same time
3. C.Only after the user flow emits twice
4. D.After 2 seconds, once both have a value

28. Channel vs SharedFlow

Two coroutines receive from the same Channel. Five values are sent. What happens?

1. A.Both receivers get all five values
2. B.The second receiver throws an exception
3. C.Each value goes to only one of the receivers
4. D.Values are dropped until a third receiver joins

29. Value stuck after the id changes

A composable computes a formatted report with remember { format(order) }. When order changes, the old text stays. What fixes it?

1. A.rememberSaveable { format(order) }
2. B.LaunchedEffect(Unit) { format(order) }
3. C.remember(order) { format(order) }
4. D.derivedStateOf without remember

30. Mixed item types in a LazyColumn

A feed LazyColumn mixes headers, ads and posts. What does setting contentType on items help with?

1. A.Sorting the feed items by their declared type
2. B.Reusing compositions only among items of one type
3. C.Loading each type of item from the network
4. D.Making each item type scroll on its own

31. Launching from a click handler

On button click you want to call a suspend function that scrolls a list. Why can’t you use LaunchedEffect inside onClick, and what do you use?

1. A.LaunchedEffect only runs on IO; use GlobalScope.launch
2. B.Suspend calls are not allowed in Compose at all
3. C.onClick is already a coroutine, so just call it
4. D.LaunchedEffect is composable-only; use rememberCoroutineScope().launch

32. Clicking a button in a Compose test

In a Compose UI test, how do you find the "Pay" button reliably and click it, even if its label is translated?

1. A.Use Espresso onView(withId(R.id.pay)).perform(click())
2. B.Find it by its x and y screen position and tap there
3. C.Set testTag("pay"), then onNodeWithTag("pay").performClick()
4. D.Call the button’s onClick lambda directly by reflection

33. Handling the Android back button

A full-screen photo editor should ask "Discard changes?" when the Android hardware back button is pressed. Which API lets you intercept it?

1. A.Keyboard.addListener with the hardwareBack event name
2. B.AppState change events with the back state
3. C.Linking.addEventListener for the back URL
4. D.BackHandler, returning true from the listener to stop the default

34. What triggers an ANR

An Android app shows "App isn't responding". What is the typical trigger for an input-dispatch ANR?

1. A.A background thread runs for more than one full minute
2. B.The app uses more than 100 MB of memory
3. C.A network call returns an HTTP 500 error
4. D.The main thread does not handle input for about 5 seconds

35. Layouts for tablets and foldables

An app must work on phones, foldables and tablets. What do Android's window size classes help with?

1. A.Deciding how much RAM to request from the system
2. B.Choosing layouts by available window width, not device type
3. C.Setting a different app icon for each screen size
4. D.Locking the app to portrait mode on large screens

36. Which app process is killed first

Memory is low on an Android phone. Which process is the system most likely to kill first?

1. A.A cached app that the user left a while ago
2. B.The app currently in the foreground
3. C.An app running a visible foreground service
4. D.The system UI that draws the status bar

37. User grants only approximate location

On Android 12+, an app requests ACCESS_FINE_LOCATION and ACCESS_COARSE_LOCATION. The user picks "Approximate". What should the app expect?

1. A.Only coarse location is granted, so the app must cope with it
2. B.The request fails and no location at all is granted to it
3. C.Fine location is granted anyway after 24 hours
4. D.The app is forced to close by the system

38. Cleartext HTTP fails on Android

A new Android app calls an HTTP (not HTTPS) test server and gets "Cleartext HTTP traffic not permitted". Why?

1. A.Android blocks all network traffic in debug builds
2. B.Apps targeting API 28+ block cleartext traffic by default
3. C.HTTP only works on Android when the phone is on Wi-Fi
4. D.The INTERNET permission must be requested at runtime

39. Obfuscated Android crash traces

Crash reports from a release Android build show names like `a.b.c.d(Unknown Source)`. What makes them readable?

1. A.Uploading the R8 mapping.txt for that build to the crash tool
2. B.Turning off minification in the next release only
3. C.Asking users to send screenshots of each crash
4. D.Building the release on a faster CI machine

40. Data loaded again and again

A tab’s .onAppear starts a network load. Users report it reloads each time they switch tabs. Why?

1. A.onAppear runs each time the view appears, not once
2. B.onAppear runs on every frame of animation
3. C.TabView recreates the app on each switch
4. D.Network calls repeat automatically in SwiftUI

41. Testing process death

A checkout screen works after rotation but loses the cart when the user returns after a long time in another app. What is happening and how do you fix it?

1. A.The ViewModel was garbage collected because of a memory leak; add more RAM
2. B.The OS killed the backgrounded process; the ViewModel was lost, so save key state with SavedStateHandle or persistent storage and restore it
3. C.The user cleared the app cache manually; nothing can be done
4. D.Rotation and backgrounding are the same, so the bug must be on the server

42. Slow cold start

An Android app takes 3 seconds to show its first screen on a cold start. Profiling shows many SDKs initialised in Application.onCreate. What is the most effective improvement?

1. A.Defer or lazily initialise non-critical SDKs, move work off the main thread, and add a Baseline Profile
2. B.Show a longer splash screen animation
3. C.Increase minSdk to the latest version
4. D.Move all code into one large Activity

43. Collecting a cold Flow twice

What does this Kotlin program print, one value per line?

val numbers = flow {
  println("start")
  emit(1)
  emit(2)
}

fun main() = runBlocking {
  numbers.collect { println(it) }
  numbers.take(1).collect { println(it) }
}

1. A.start, 1, 2, 1
2. B.start, 1, 2, start, 1, 2
3. C.1, 2, 1
4. D.start, 1, 2, start, 1

44. PendingIntent crash on Android 12

After targeting Android 12 (API 31) or higher, creating a PendingIntent with flags set to 0 crashes the app. Why?

1. A.PendingIntent was removed in Android 12
2. B.The app needs the SCHEDULE_EXACT_ALARM permission for every PendingIntent it creates, including ones used for notifications and widgets
3. C.You must explicitly pass FLAG_IMMUTABLE or FLAG_MUTABLE; prefer FLAG_IMMUTABLE unless another app must fill in parts of the intent
4. D.PendingIntent flags must be negative numbers

45. Foreground service fails on Android 14

Your app targets Android 14 (API 34). Starting a foreground service that tracks a running workout now throws an exception. What is required?

1. A.Declare a foregroundServiceType for the service in the manifest (such as health or location) and request the matching FOREGROUND_SERVICE_* permission
2. B.Nothing can be done; foreground services are banned on Android 14
3. C.Replace the service with a manifest BroadcastReceiver, because Android 14 only allows long-running work such as workout tracking inside receivers
4. D.Show a Toast before calling startForeground

46. Exported activity loading any URL

An exported Android activity reads a "url" extra from its intent and loads it in a WebView with JavaScript enabled and a JavaScript interface to native code. What is the risk?

1. A.None; exported only controls whether the activity gets a launcher icon, and other apps can never start an activity in a different app with their own extras
2. B.Only slower page loads
3. C.Exported only matters on rooted phones
4. D.Any installed app can launch it with a malicious URL that then calls the native bridge; validate the URL against an allowlist, or set exported to false if outside apps do not need it

47. FCM handler skipped in background

You send FCM messages with a "notification" block plus data. When the Android app is in the background, onMessageReceived is not called and your custom handling never runs. Why?

1. A.FCM is disabled for apps in the background
2. B.Background delivery needs the RECEIVE_BOOT_COMPLETED permission, and without it FCM drops every message for apps that are not in the foreground
3. C.In the background, the system itself shows messages that have a notification block and skips onMessageReceived; send data-only messages if the app must handle them
4. D.onMessageReceived only works in debug builds

48. Data class holding an array

Why does Photo(1, byteArrayOf(1, 2)) == Photo(1, byteArrayOf(1, 2)) return false?

1. A.Data classes are not allowed to hold arrays
2. B.Generated equals() compares arrays by reference
3. C.The first property is compared as a string
4. D.byteArrayOf fills arrays with random contents

49. Handler on a child coroutine

A crash still happens even though the inner launch has a CoroutineExceptionHandler. Why?

scope.launch {
    launch(CoroutineExceptionHandler { _, e -> log(e) }) {
        throw IOException("boom")
    }
}

1. A.CoroutineExceptionHandler works only with async builders
2. B.The handler must be the first element in every context
3. C.Handlers are always ignored when running on Dispatchers.IO
4. D.Children pass errors to the parent; handlers work at the root

50. Child list never skips

OrderList recomposes every time the parent does, even when orders did not change. Why?

@Composable
fun OrdersScreen(orders: List<Order>, query: String) {
    SearchBar(query)
    OrderList(orders.filter { it.isActive })
}

1. A.LazyColumn always recomposes along with its parent
2. B.Composables with list parameters can never skip
3. C.The theme forces every child to recompose each time
4. D.filter returns a new list instance, so it looks changed

51. Content under the status bar

After raising targetSdk to 35, screens on Android 15 draw under the status and navigation bars. Why?

1. A.It is a bug in Android 15 that a patch will fix
2. B.The app theme lost its colorPrimary attribute
3. C.Apps targeting 35 are edge-to-edge; handle insets
4. D.targetSdk 35 removes support for all toolbars

52. Decryption fails after new fingerprint

An app encrypts a token with a Keystore key that requires biometric authentication. After the user adds a new fingerprint, decryption fails with KeyPermanentlyInvalidatedException. Why?

1. A.All Keystore keys expire automatically after 30 days
2. B.New biometric enrollment invalidates such keys by default
3. C.The token was stored in the wrong app folder
4. D.Adding a fingerprint deletes all app data

53. Manifest receiver never fires

A receiver declared in the manifest for an implicit broadcast stopped working when the app targeted Android 8.0+. What should it use instead?

1. A.A higher priority value in the intent filter
2. B.android:exported="false" set on the receiver
3. C.A sticky broadcast sent from the app itself
4. D.A runtime-registered receiver or WorkManager

54. Observer called twice after back

A fragment observes LiveData with observe(this) in onViewCreated. After navigating away and back, each update fires the callback twice. Why?

1. A.The fragment outlives its view; use viewLifecycleOwner
2. B.LiveData always delivers each value twice
3. C.onViewCreated runs twice per view creation
4. D.The ViewModel was created twice by mistake

55. Duplicate screens from notification taps

Tapping a chat notification several times stacks several copies of the same ChatActivity. What prevents duplicates when it is already on top?

1. A.Start it with FLAG_ACTIVITY_SINGLE_TOP and handle onNewIntent
2. B.Call finish() in onCreate of every ChatActivity
3. C.Declare the activity with android:exported set to false
4. D.Use FLAG_ACTIVITY_NO_ANIMATION on the intent

56. Periodic sync every 5 minutes

A developer schedules a WorkManager PeriodicWorkRequest to sync every 5 minutes, but it runs only about every 15 minutes. Why?

1. A.WorkManager rounds all intervals up to one hour
2. B.The minimum repeat interval for periodic work is 15 minutes
3. C.The phone must be charging for periodic work to run
4. D.Periodic work only runs while the app is visible

57. Gallery app on Android 13

A gallery app targeting Android 13 still requests READ_EXTERNAL_STORAGE and cannot see images. What changed?

1. A.Android 13 removed app access to images completely
2. B.It must request READ_MEDIA_IMAGES and READ_MEDIA_VIDEO
3. C.It must request the CAMERA permission instead
4. D.Images are only visible after the phone reboots

58. Exposing native code to a WebView

An Android app calls `addJavascriptInterface(bridge, "App")` on a WebView that can navigate to any URL. What is the danger?

1. A.The WebView will refuse to load any HTTPS pages
2. B.Any page loaded in it can call the exposed native methods
3. C.JavaScript is disabled as soon as a bridge is added
4. D.The bridge works only with local HTML files

59. Attacker installs a CA certificate

An attacker convinces a user to install a custom CA certificate on an Android 13 phone to intercept your app's HTTPS traffic. By default, what happens?

1. A.All apps trust the new CA and all traffic is readable
2. B.Apps targeting API 24+ ignore user-added CAs by default
3. C.The phone wipes itself when a CA is installed
4. D.Only Wi-Fi traffic is affected, not mobile data

60. Raising the minimum OS version

An app raises minSdk from 24 to 26. What happens to users on Android 7.0 devices (API 24)?

1. A.They keep their installed version but receive no further updates
2. B.Their installed copy is uninstalled automatically by Play
3. C.Their app keeps updating, but new features are hidden
4. D.They are moved to the beta track automatically