Android Interview Questions

900+ questions across Android, Kotlin, Compose, Architecture, DSA, System Design, Behavioral, and Coding Tests.

Android Platform

Activity & Fragment Lifecycle

Walk me through the Activity lifecycle callbacks and what each one is meant for.
What happens when the user rotates the device?
What is the difference between onSaveInstanceState and onRestoreInstanceState?
How does ViewModel survive configuration changes?
What happens when Activity A starts Activity B? Walk through the callback order.
What happens during process death? How is it different from a configuration change?
What’s the difference between ViewModel and SavedStateHandle?
List the Fragment lifecycle callbacks. How do they differ from Activity?
What is viewLifecycleOwner in a Fragment and why does it matter?
Why should Fragments only use the default no-argument constructor?
Why do I call setContentView() only in onCreate?
Explain onNewIntent. When is it called?
When does onDestroy get called without onPause and onStop?
How does multi-window mode affect the lifecycle?
How does ViewModel scoping work?
What are lifecycle-aware components?
Can a Fragment’s lifecycle state exceed its host Activity’s state?
What is the Fragment Result API?
What is setRetainInstance(true) and why is it deprecated?
What is ProcessLifecycleOwner?
What’s the difference between FragmentTransaction add() and replace()?
How do you test Activity lifecycle behavior?

Android Components

What are the four core Android components?
What is the Service lifecycle?
What are the three types of Services in Android?
What is the difference between startService() and bindService()?
Services run on the main thread — what does that mean?
What does onStartCommand() return and what do the return values mean?
When should you use Service vs WorkManager?
What are the Foreground Service requirements on modern Android?
What is the AndroidManifest.xml and what must be declared in it?
What is a Broadcast Receiver and how do you register one?
What changed with implicit broadcast restrictions in Android 8.0+?
What is a Content Provider and when would you use one?
What is android:exported and why does it matter?
Explain Application Context vs Activity Context.
What is the Binder mechanism and how does IPC work?
What is AIDL and when would you use it over Messenger?
What is FileProvider and why is it needed?
What happened to LocalBroadcastManager and what replaced it?
What is an Intent and what are the types?
What are PendingIntents and when do you use them?
What are ordered broadcasts vs normal broadcasts?

What is an Intent in Android?
What’s the difference between explicit and implicit intents?
What are the four launch modes?
What is an Intent Filter and how does the system match them?
How do you pass data between Activities using intents?
Parcelable vs Serializable — when do you use which?
What is a PendingIntent?
How do Intent flags interact with manifest launch modes?
What happens inside onNewIntent()?
What’s the difference between setData() and putExtra()?
What are FLAG_IMMUTABLE and FLAG_MUTABLE?
What is task affinity?
What is a Sticky Intent? Is it still relevant?
What is the difference between deep links and App Links?
Walk through the back stack behavior for each launch mode.
What happens when you use FLAG_ACTIVITY_CLEAR_TOP with standard launch mode?
What security concerns exist with implicit intents and PendingIntents?
What is singleInstancePerTask?
How do you handle deep links in a single-Activity architecture?
What is a deferred deep link?
How does android:exported affect intent delivery?
What’s the difference between FLAG_ACTIVITY_NEW_TASK and FLAG_ACTIVITY_CLEAR_TASK?

Views, RecyclerView & Custom UI

What is the ViewHolder pattern, and why is it mandatory in RecyclerView?
Walk through the three key methods of RecyclerView.Adapter.
What are the three phases of the View rendering pipeline?
What is the difference between invalidate() and requestLayout()?
What is DiffUtil and why should you use it instead of notifyDataSetChanged()?
What is the difference between DiffUtil, AsyncListDiffer, and ListAdapter?
Explain how RecyclerView’s view recycling mechanism works internally.
How do you handle multiple view types in RecyclerView?
What’s the difference between RecyclerView and the old ListView?
What are the three built-in LayoutManagers, and when would you use each?
What does onMeasure() do, and what are the three MeasureSpec modes?
Explain the touch event dispatch mechanism — dispatchTouchEvent, onInterceptTouchEvent, and onTouchEvent.
What’s the 16ms frame budget, and what happens when you exceed it?
What is overdraw, and how do you detect and reduce it?
How do you flatten a view hierarchy and why does it matter?
What is RecycledViewPool and how can you share it between nested RecyclerViews?
How do you resolve touch conflicts between a parent ScrollView and a child RecyclerView?
What is ItemDecoration and how does it work?
How does ItemAnimator work in RecyclerView?
When would you create a custom View, and what’s the difference between extending View vs ViewGroup?
What is ViewStub and when would you use it?
What is SnapHelper in RecyclerView and how does it work?
What is hardware acceleration and what are its limitations?

Threading & Background Work

What is the main thread in Android and why can’t you block it?
What is an ANR and how do you diagnose it?
What are Handler, Looper, and MessageQueue?
What is WorkManager and when should you use it?
What is the difference between WorkManager, AlarmManager, and foreground services?
What are the different types of work requests in WorkManager?
What is the difference between Worker, CoroutineWorker, and ListenableWorker?
What happens to WorkManager tasks when the device reboots?
What is Doze mode and how does it affect background work?
How did background work restrictions evolve across Android versions?
What are the foreground service type requirements in Android 14?
What is HandlerThread and when would you use it?
What is Expedited Work in WorkManager?
How would you handle a long-running upload that survives process death?
How does WorkManager decide which scheduling mechanism to use?
How does MessageQueue work at the native level?
What is the difference between a Service and an IntentService?
How do you prevent duplicate work in WorkManager?
What are the exact alarm restrictions in Android 12+?
How do you observe WorkManager progress and status from the UI?
How do you reduce battery drain from background work?

Storage & Data Persistence

What are the main options for persisting data on Android?
What is SharedPreferences and how does it work internally?
What is the difference between commit() and apply() in SharedPreferences?
What are the problems with SharedPreferences that led to DataStore?
What is Jetpack DataStore and how does it differ from SharedPreferences?
What is the difference between Preferences DataStore and Proto DataStore?
How would you choose between SharedPreferences, DataStore, Room, and file storage?
What are the three main components of Room?
How does Room enforce main-thread safety?
How do Room database migrations work?
What is the @Transaction annotation in Room?
How do you handle custom types in Room with TypeConverter?
How do you model relationships in Room?
What is the difference between internal storage and external storage?
What is scoped storage?
How do you share files between apps?
What is a Content Provider?
How does EncryptedSharedPreferences work?
What are database indexes in Room?
How does Room’s compile-time SQL verification work?
How do you test Room databases?
What is the Storage Access Framework (SAF)?
When should you normalize vs denormalize a database schema?
What is Write-Ahead Logging (WAL) and why does SQLite use it?

Networking & API Communication

What is the difference between OkHttp and Retrofit?
How does a network request flow through OkHttp and Retrofit?
What are OkHttp interceptors? What’s the difference between application and network interceptors?
How do you handle authentication tokens and token refresh in the network layer?
What HTTP caching strategies exist, and how does OkHttp handle them?
What is certificate pinning and why would you use it?
What is the Network Security Configuration?
How does Retrofit’s suspend function support work under the hood?
What is the difference between enqueue() and execute() in OkHttp?
How does OkHttp’s connection pooling work?
Walk through OkHttp’s built-in interceptor chain in order.
What’s the difference between Gson, Moshi, and kotlinx.serialization?
What is the difference between short polling, long polling, and WebSocket?
What is the difference between WebSocket and Server-Sent Events (SSE)?
REST vs GraphQL — when would you choose each on mobile?
How do you handle network connectivity changes and offline scenarios?
What is the difference between JSON and Protocol Buffers?
How would you implement retry with exponential backoff?
How does Retrofit’s converter system work?
How would you implement request deduplication?
What is HTTP/2 and why does it matter for mobile?
What is an unmetered network constraint and how does it affect background work?
What is the difference between FlatBuffers and JSON? When should you use FlatBuffers?
What is the difference between Webhook and Polling? When would you choose each?

Notifications, Permissions & Security

What are the different types of permissions in Android?
Walk through the runtime permission request flow. What are the edge cases?
What are notification channels and why do they matter?
How does Firebase Cloud Messaging (FCM) work?
What is the difference between data messages and notification messages in FCM?
What is the POST_NOTIFICATIONS permission introduced in Android 13?
What is the Android Keystore and why should you use it?
What is EncryptedSharedPreferences and when would you use it?
How would you implement a secure authentication flow in an Android app?
What security considerations apply when storing and transmitting user data?
How does certificate pinning protect against man-in-the-middle attacks?
How does the BiometricPrompt API work on Android?
What is the difference between OAuth 2.0, JWT, and session-based authentication?
What are the common WebView security vulnerabilities?
What is the difference between Keychain and Keystore?
What are the differences between AES, RSA, and SHA?
How do notification actions, direct reply, and bundled notifications work?
How does FCM topic messaging work?
What is Play Integrity API and when would you use it?
What is StrongBox and how does it relate to the Keystore?
What happens when a user revokes a permission while the app is running?
How does the network security config work in Android?
How do you securely store API keys in an Android app?
What is Cleartext traffic in Android and how do you restrict it?
What is the difference between Hash, Encrypt, and Encode?
What is the difference between Symmetric and Asymmetric Encryption?
What is the SMS Retriever API and how does it work?

Memory Management & Performance

What is a memory leak in Android?
How does garbage collection work on Android?
Why does an Android app lag?
What are the common causes of OutOfMemoryError?
How do you handle large bitmaps efficiently?
How would you profile and fix a janky RecyclerView?
How do you measure and optimize app startup time?
What is onTrimMemory() and how do you respond to it?
What is overdraw and how do you reduce it?
What is StrictMode?
Is it possible to force garbage collection in Android?
What is LruCache and how does it work?
What is the difference between ARGB_8888 and RGB_565?
What is R8 and how does it affect performance?
What is the difference between ART and Dalvik?
What are baseline profiles?
What is inBitmap and how does bitmap pooling work?
How does LeakCanary detect memory leaks?
What is Macrobenchmark and how does it differ from Microbenchmark?
How does hardware acceleration affect rendering?
How would you reduce APK size?
What is the difference between HashMap, ArrayMap, and SparseArray? When should you use each?
How do you use Memory Heap Dumps to diagnose memory issues?

Gradle & Build System

What is the difference between implementation, api, and compileOnly dependency configurations?
What are the three phases of a Gradle build?
What are build types and product flavors, and how do they combine?
What is the difference between build.gradle.kts at the project level vs the module level?
How does the Android build process work from source code to APK?
What is the difference between APK and Android App Bundle (AAB)?
What is the Gradle wrapper and why should you use it?
What is the difference between KSP and KAPT?
How does signing work in Android?
What are version catalogs and why are they used?
What is buildConfigField and how does it differ from resValue?
What is Multidex and why was it needed?
What is the Gradle daemon and how does it speed up builds?
What are the main strategies for reducing build time in a large Android project?
How does Gradle’s build cache work?
What is the Configuration Cache and how does it differ from the Build Cache?
What are convention plugins and why are they better than buildSrc?
What is R8 and how does it differ from ProGuard?
How would you set up a CI/CD pipeline for an Android project?
How do you handle dependency conflicts in Gradle?
What is settings.gradle.kts and what does dependencyResolutionManagement do?
What is the difference between includeBuild and include in settings?
What is desugaring in Android and why is it needed?
What is the difference between annotationProcessor, KAPT, and KSP?
What is a Build Variant in Android?

Android Internals & Process Management

What is ART and how does it differ from Dalvik?
What is the difference between cold start, warm start, and hot start?
What is the app startup sequence from tap to first frame?
What is an ANR and what are the thresholds?
What are the most common causes of ANRs?
What is the Zygote process?
What is the Application class and when is it initialized?
What is the process importance hierarchy?
How does Android handle process death and restoration?
What is Binder IPC?
What is a DEX file?
What is Multidex and why is it needed?
How does ContentProvider initialization affect app startup?
What is AIDL and how is it different from Messenger?
What is the Low Memory Killer?
What is the oom_adj_score and how is it assigned?
What is ActivityThread and what role does it play?
What happens internally when you call startActivity()?
How does Zygote preloading work under the hood?
What is the Binder thread pool and what happens when it’s exhausted?
What is profile-guided optimization in ART?
What is android:process and what are the implications of using a separate process?
How does the DEX file layout affect startup performance?
What is the 16 KB page size change in Android 15?

What is a deep link in Android?
What are the three types of deep links on Android?
What is the difference between a deep link and an App Link?
How do you set up a basic deep link intent filter?
How do you read data from an incoming deep link?
What is the Digital Asset Links file and where does it go?
How do you configure an App Link in the manifest?
What changed with deep link behavior on Android 12?
How does Android verify App Links at install time?
What happens when App Link verification fails?
What happens when multiple `` elements are in the same intent filter?
What is the difference between pathPrefix, path, and pathPattern?
What is a custom URI scheme and what are its limitations?
How do you test deep links during development?
How do deep links work with the Navigation component?
What is the difference between explicit and implicit deep links in the Navigation component?
How does deep link handling differ in Compose navigation?
How do you handle deep links that require authentication?
What are deferred deep links and how do they work?
How do you handle deep links in multi-module navigation?
What is DomainVerificationManager and when would you use it?
How do you support deep links across product flavors with different package names?

Sensors, Camera & Hardware APIs

What is CameraX and how does it differ from Camera2?
How do you set up a camera preview using CameraX?
What location permissions does Android require?
What is the Fused Location Provider and why use it over raw GPS?
How does the BiometricPrompt API work?
What are the three categories of sensors in Android?
How do you access sensor data in Android?
What is the difference between the accelerometer and the gyroscope?
What is the difference between Bluetooth Classic and BLE?
How does Android handle location in the background?
What is geofencing in Android?
What is the CameraX ImageAnalysis use case?
What is the difference between MediaPlayer and ExoPlayer?
How would you implement a step counter?
How does the sensor sampling rate work?
What is NFC and how is it used in Android?
How do you handle BLE communication — scanning, connecting, and reading data?
What is the proximity sensor used for?
How do you filter noisy sensor data?
What are the Camera2 API’s core concepts?
How do you check if a sensor is available before using it?
What permissions are needed for Bluetooth on modern Android?
What is the ACTIVITY_RECOGNITION permission?

Accessibility & Localization

What is accessibility in Android and why does it matter?
What is contentDescription and when should I use it?
What are content description best practices?
What is TalkBack and how does it work?
What is the minimum touch target size recommended by Android?
What is the difference between importantForAccessibility and contentDescription = null?
What is color contrast ratio and how does it affect accessibility?
How do I handle localization using string resources?
What is RTL support and how do I implement it?
How do I handle plurals in string resources?
How do I handle formatting differences across locales?
What is the difference between a crash and an ANR, and how do I debug each?
What are Android vitals?
What is StrictMode and how does it help with app quality?
How do I test accessibility on Android?
How do semantics work in Jetpack Compose for accessibility?
How do I merge and clear semantics in Compose?
What are live regions and custom accessibility actions?
How does per-app language selection work?
How does crash reporting work under the hood?
What are app quality guidelines and how do they differ from core vitals?
What is AccessibilityDelegate and when would I use it?
How do I handle dynamic text sizing for accessibility?

Kotlin

Basics & Type System

What is the difference between val and var?
How does null safety work in Kotlin?
What is the difference between == and === in Kotlin?
What are smart casts in Kotlin?
What is the difference between as and as? for casting?
Explain Kotlin’s type hierarchy — Any, Unit, and Nothing.
What is the difference between Any and Any? in the type hierarchy?
What is a data class and what methods does it generate?
How do copy() and componentN() work in data classes?
What is the difference between sealed class and enum class?
What is the difference between sealed class and sealed interface?
What is a value class and when would you use it?
Explain the object keyword — singleton, companion object, and anonymous object.
What is the difference between lateinit and lazy?
How does lateinit work under the hood?
What is const val and how is it different from val?
What is the difference between companion object and top-level functions?
What is a typealias and how is it different from a value class?
What is the String Pool on the JVM and how does it affect Kotlin string comparisons?
What are Labels in Kotlin? How do you use break@label, continue@label, and return@label?
What are property delegates in Kotlin? Explain Delegates.observable, Delegates.vetoable, and Delegates.notNull.

Functions & Scope Functions

What is a higher-order function?
What is a lambda expression? What does it mean?
What is the difference between a lambda and an anonymous function?
What are the five scope functions and how do they differ?
When should you use let vs apply vs also?
What is the difference between run and with?
What is an extension function?
How are extension functions resolved — statically or dynamically?
Can you write an extension function on a nullable type?
What is an infix function?
What is an inline function and why does it matter for performance?
What is a reified type parameter and why does it require inline?
What is non-local return in inline functions?
What are crossinline and noinline?
What is the tailrec modifier?
What is a function reference and when is it better than a lambda?
What is the difference between T.() -> Unit and (T) -> Unit as a function type?
How do scope functions behave with nullable receivers?
When should you NOT use inline functions?
What happens under the hood when you pass a lambda to a non-inline higher-order function?

Collections, Sequences & Functional Patterns

What is the difference between List and MutableList in Kotlin?
What does map do, and how is it different from flatMap?
What is the difference between fold and reduce?
Explain groupBy and associateBy. When do you use each?
What do partition, chunked, and windowed do?
What is destructuring in Kotlin and how does it work?
What is operator overloading in Kotlin?
What is the by keyword in Kotlin? What are property delegates?
Explain Sequence vs Iterable. When does using a Sequence matter?
What are intermediate and terminal operations on a Sequence?
What is the difference between Sequence and Flow?
How does lazy delegation work internally?
How do observable and vetoable delegates work?
How do you write a custom property delegate?
Explain class delegation with the by keyword.
How does the order of collection operations affect performance?
How do you transform a Map using Kotlin’s collection functions?
What does buildList do and why is it useful?
What is the difference between associate, associateBy, and associateWith?

Generics, Variance & Reified Types

What are generics in Kotlin and why do we need them?
What is type erasure and how does it affect generics?
What does covariance mean? Explain the out keyword.
What does contravariance mean? Explain the in keyword.
What is the PECS principle and how does it apply in Kotlin?
How does variance work with MutableList vs List?
What is the difference between star projection and a generic type?
What are generic constraints and the where clause?
What is the difference between declaration-site and use-site variance?
What is the reified keyword and why does it require inline?
Can you use reified with classes?
How does Nothing type work in generics?
What are the differences between Class, KClass, and reified T?
Explain type projection with a real example.
What happens when you combine multiple generic constraints with variance?

Kotlin Under the Hood

How does Kotlin compile to JVM bytecode?
What happens to a data class at the bytecode level?
How does a companion object compile?
What does @JvmStatic actually do?
What does @JvmField do?
What is @JvmOverloads and when is it needed?
How does Kotlin’s null safety work at the bytecode level?
How does a sealed class compile?
What is the difference between sealed class and sealed interface at the bytecode level?
How does the suspend function CPS transformation work?
How does the compiler turn a suspend function into a state machine?
How do inline functions work at the bytecode level?
How does a lambda compile to bytecode?
What is SAM conversion and how does it work?
How does the when expression compile?
How does the delegation pattern compile?
How do inline value classes work at the bytecode level?
How does property delegation compile?
What is @JvmName and when would you use it?
How does a coroutine suspension point differ from a regular function call in bytecode?

Contracts, DSLs & Advanced Patterns

What is the Result type in Kotlin?
How do sealed classes help with error handling?
How does Result compare to sealed classes for error handling?
What is class delegation and how does it differ from inheritance?
What is interface delegation and the Decorator pattern?
What is a DSL in Kotlin and what makes it possible?
What is @DslMarker and why is it important?
How do you build a type-safe builder?
What are Kotlin contracts and what problem do they solve?
What does callsInPlace do in a contract?
What does returns implies do?
What are context receivers (context parameters)?
What are the limitations of Kotlin contracts?
How do sealed hierarchies work with exhaustive when expressions?
How does the delegation pattern compare to dependency injection?
How do scope functions relate to DSL building?
What are inline value classes and when would you use them?

Kotlin Coroutines & Flows

Coroutines Basics

What are Kotlin Coroutines and why use them over threads?
What is a suspend function?
What is a CoroutineScope?
What is the difference between launch and async?
What are Dispatchers? Explain each one.
What is withContext and when do you use it?
What is structured concurrency?
What is a Job and what are its lifecycle states?
What is the difference between join and cancel on a Job?
What is SupervisorJob and how is it different from a regular Job?
What is the difference between coroutineScope and supervisorScope?
What is CoroutineContext and what does it contain?
What is runBlocking and when should you use it?
How does viewModelScope work internally?
What is Dispatchers.Main.immediate and how is it different from Dispatchers.Main?
What is the difference between GlobalScope and a custom CoroutineScope?
How do you run two suspend functions in parallel?
Can you call a suspend function from a regular function?
How does structured concurrency prevent coroutine leaks?

Coroutines Advanced

How does exception handling work in coroutines?
How do exceptions propagate in a coroutine hierarchy?
How does coroutine cancellation work? What does “cooperative cancellation” mean?
What is the difference between ensureActive() and yield()?
What happens when you cancel a coroutine doing CPU-intensive work with no suspension points?
What is NonCancellable and when would you use it?
What is CPS transformation and how does the compiler handle suspend functions?
How does the compiler generate a state machine for suspend functions?
What is Mutex and how is it different from synchronized?
What is Semaphore and how does it differ from Mutex?
Explain Channel types — Rendezvous, Buffered, Conflated, and Unlimited.
How does the select expression work?
What is suspendCoroutine and when do you use it?
What is suspendCancellableCoroutine and how does it differ?
How do you convert a multi-shot callback API into a Flow?
How does withContext actually switch threads?
What is the difference between coroutineScope and supervisorScope for exception handling?

Cold Flows & Operators

What is a Flow and why is it called “cold”?
What are the different ways to create a Flow?
What are terminal operators?
What are intermediate operators? How do map, filter, and transform work?
How do take, zip, combine, and merge differ?
What does flowOn do and why is it important?
What is onStart and onCompletion?
How does the catch operator work?
How do retry and retryWhen work?
What is the difference between buffer and conflate?
What are the buffer overflow strategies?
How does debounce work?
What does distinctUntilChanged do?
Explain flatMapConcat, flatMapMerge, and flatMapLatest.
What happens if you throw an exception inside the collect block?
What is the execution order when chaining flow operators?

Hot Flows, StateFlow & SharedFlow

What is the difference between a cold flow and a hot flow?
What is StateFlow and how does it differ from SharedFlow?
What are MutableSharedFlow and MutableStateFlow?
When would you use SharedFlow instead of StateFlow?
What does the replay parameter in SharedFlow do?
What is callbackFlow?
What is channelFlow and how does it differ from callbackFlow?
What are the SharingStarted strategies?
What is the difference between stateIn and shareIn?
How do you safely collect flows in an Activity or Fragment?
What is flowWithLifecycle?
What is collectAsStateWithLifecycle in Compose?
How does SharedFlow handle backpressure?
How does WhileSubscribed(5_000) survive configuration changes?
How do you handle one-shot events like navigation using flows?
What is the difference between conflate() and collectLatest?
What converts a cold flow to hot when using stateIn inside a ViewModel?
What is the subscriptionCount property on SharedFlow?
Can you create a custom SharingStarted strategy?

Jetpack Compose

Fundamentals & Thinking in Compose

What is Jetpack Compose?
What is a @Composable function?
What is the difference between declarative and imperative UI?
How does Compose differ from the XML View system?
What does “composition over inheritance” mean in Compose?
What is Composition in Compose?
What is recomposition?
What happens during initial composition vs recomposition?
What are the three phases of Compose?
What is @Preview and how does it work?
What is the difference between remember and mutableStateOf?
How does remember work internally?
Why does Compose use functions instead of classes for UI components?
What is the role of the Compose compiler plugin?
What is the difference between Compose Runtime and Compose UI?
How does Compose decide to skip a composable during recomposition?
What is positional memoization?
What is the slot table?
How does the Compose compiler transform @Composable functions at bytecode level?
Can composable functions run in parallel?

State Management

What is state in Jetpack Compose?
How do you retain data in composable functions?
What is mutableStateOf and how does it work?
What is the difference between remember and rememberSaveable?
How do you save custom objects with rememberSaveable?
What is state hoisting in Compose?
What is unidirectional data flow (UDF) in Compose?
What are mutableStateListOf and mutableStateMapOf?
What is derivedStateOf and when should you use it?
How does derivedStateOf differ from computing a value in the composable body?
What is snapshotFlow and when do you use it?
What is the difference between collectAsStateWithLifecycle and collectAsState?
When should you use a ViewModel vs a state holder class?
How should you structure state in a ViewModel for Compose?
What is the difference between using State vs StateFlow in a ViewModel?
How does state restoration work after process death?
How does the snapshot system work under the hood?
What is the right way to expose one-time events from ViewModel to UI?
How do you handle text field state efficiently in Compose?
What happens if you forget to wrap mutableStateOf with remember?
What happens to remember state when a composable leaves and re-enters the composition?
What is StateFlow and how does it differ from LiveData?
What is the difference between UI state and data state?
What is SharedFlow and when do you use it instead of StateFlow?
What is the single state object pattern?
What is SavedStateHandle and why do you need it?
How does process death differ from configuration changes?
How does stateIn work and what is the right SharingStarted strategy?
When should you use multiple flows instead of a single state object?
How does Redux-style state management (MVI) work in Android?
What is a state machine and how do you implement one in Android?
How does the Compose snapshot system relate to state management?
How do you handle state restoration after process death in Compose?
What is unidirectional data flow and why does it matter for state management?

Side Effects & Lifecycle

What is a side effect in Compose?
What is the Compose lifecycle?
What is LaunchedEffect and when do you use it?
What is DisposableEffect and how is it different from LaunchedEffect?
What is SideEffect and when do you use it?
What is the difference between rememberCoroutineScope and LaunchedEffect?
What is rememberUpdatedState and why is it needed?
What is the difference between LaunchedEffect(Unit) and LaunchedEffect(true)?
What is produceState?
What is snapshotFlow?
How does the Compose lifecycle relate to the Activity lifecycle?
How do you handle one-time events like navigation and snackbars?
How does Compose handle effects during configuration changes?
What is the key() composable and when do you need it?
How do multiple LaunchedEffects work in the same composable?
What happens when you call effects conditionally?
How does process death affect Compose state?
What is movableContentOf and how does it interact with lifecycle?
What is the difference between collectAsState and collectAsStateWithLifecycle?
What is the order of execution between SideEffect, LaunchedEffect, and DisposableEffect?
How do you handle back press events in Compose?

Recomposition, Stability & Performance

What triggers recomposition?
What is smart recomposition?
What is the stability system in Compose?
What is the difference between @Stable and @Immutable?
Why are collections like List<> considered unstable by default?
How does Compose handle interfaces for stability?
Why should I use viewModel::onClick instead of { viewModel.onClick() } in composables?
How does Compose compare parameters to decide whether to skip recomposition?
What is donut-hole skipping?
What is strong skipping mode?
What are the common performance mistakes with recomposition?
How does the Compose runtime handle recomposition scheduling?
How do I use graphicsLayer for performance?
What is the slot table and how does Compose use it?
How do I use the Compose compiler reports to diagnose stability issues?
How do I debug recomposition issues in a running app?
What is the stability configuration file?
What is movableContentOf?
How does derivedStateOf help reduce unnecessary recompositions?

Layouts, Modifiers & Custom Drawing

What is the difference between Row, Column, and Box?
How does the weight modifier work in Row and Column?
Why does modifier order matter in Compose?
What happens when you apply size modifiers in different positions in the chain?
What is the difference between offset and padding?
What are the three phases of Compose rendering?
How does clip work in Compose?
How do you create a custom shape for clipping?
What is graphicsLayer and when would you use it?
What are the three main drawing modifiers in Compose?
What is Canvas in Compose and how is it different from Android’s Canvas?
What is Brush in Compose?
How does the modifier chain work internally?
How does the Layout composable work?
What is the difference between the layout modifier and the Layout composable?
What is the difference between Modifier.layout and Modifier.offset for positioning?
What are intrinsic measurements and when are they needed?
What is SubcomposeLayout and how does LazyColumn use it?
How do alignment lines work in custom layouts?
What is CompositingStrategy in graphicsLayer?
What are Window Size Classes and how do you build adaptive layouts?
How does ConstraintLayout work in Compose?

Animation APIs

What is animate*AsState and when do you use it?
How does AnimatedVisibility work?
What is the difference between AnimatedContent and Crossfade?
What does animateContentSize do?
What is the difference between spring, tween, and keyframes animation specs?
What is rememberInfiniteTransition and when do you use it?
How do you use updateTransition for coordinated animations?
What is Animatable and how is it different from animate*AsState?
How do you create sequential and concurrent animations?
How does Compose handle interrupted animations?
What happens to animations during recomposition? How do you prevent resets?
When should you use graphicsLayer for animations instead of regular modifiers?
How do you animate items in a LazyColumn?
What are shared element transitions in Compose?
How do you build gesture-driven animations?
What is the difference between animateDecay and animateTo?
How would you implement a shimmer loading effect?
How do you animate navigation transitions in Compose?
How does Compose’s animation system compare to the View system?

What are the core components of Navigation Compose?
How does type-safe navigation work in Navigation Compose?
How do you pass arguments between navigation destinations?
What is popUpTo and how does back stack management work?
What is Material3 theming in Compose?
How do you handle dark theme and light theme switching?
How does dynamic color work in Material3?
What is CompositionLocal and when should you use it?
What is the difference between compositionLocalOf and staticCompositionLocalOf?
How do you create and provide a custom CompositionLocal?
How do you handle navigation events and avoid duplicate navigation?
How do you implement bottom navigation with Navigation Compose?
How do you handle deep links in Navigation Compose?
How does nested navigation work and when should you use it?
How does NavBackStackEntry manage lifecycle and ViewModel scoping?
How do you scope a ViewModel to a navigation graph instead of a single destination?
How does MaterialTheme work internally with CompositionLocal?
How would you implement a custom theming system beyond MaterialTheme?
What are the tradeoffs of ViewModel vs the Presenter pattern?
What is Navigation 3 and how is it different from Navigation Compose?

Testing & Accessibility

What is ComposeTestRule and how do you set up a Compose UI test?
What is the difference between createComposeRule and createAndroidComposeRule?
How do node finders work in Compose tests?
What are the most common assertions and actions in Compose tests?
What is the semantic tree and why does it matter for testing?
What is Modifier.testTag and when should you use it?
How do you handle scrolling in Compose tests?
How do you handle async operations in Compose tests?
How do you test composables that depend on a ViewModel?
What are common testing pitfalls in Compose?
How do you test navigation in Compose?
How do you set up Compose testing with Hilt?
What are semantics in Compose and how do they support accessibility?
How do you set contentDescription correctly in Compose?
What are the merged and unmerged semantic trees?
What are semantic roles and when do you set them?
How do you control traversal order for accessibility?
What are live regions in Compose accessibility?
How do you test accessibility properties in Compose tests?
What is screenshot testing and how does Paparazzi work for Compose?
How does Compose Preview testing work?

Architecture & Design

Clean Architecture & SOLID Principles

What is Clean Architecture?
What are the three main layers in Clean Architecture for Android?
What are the SOLID principles?
What is the Single Responsibility Principle in practice?
What is the dependency rule?
What is a Use Case?
What is the Repository pattern in Clean Architecture?
What is the difference between domain models, DTOs, and entities?
What is the Dependency Inversion Principle and how does it relate to Clean Architecture?
What is the difference between Clean Architecture and MVVM?
What is the Interface Segregation Principle in practice?
Is the domain layer always necessary?
How do you structure packages in Clean Architecture?
What is the mapper pattern and why does Clean Architecture use it?
How do you handle errors across layers in Clean Architecture?
How do SOLID principles apply to a real ViewModel?
How do you handle data shared across multiple screens?
What is the Open-Closed Principle in practice?
What is the Liskov Substitution Principle violation in Android?

MVVM, MVI & Architecture Patterns

What is MVVM?
What is a ViewModel and why does it survive configuration changes?
What is the difference between LiveData and StateFlow for UI state?
What is MVI?
What is the difference between MVVM and MVI?
What is unidirectional data flow?
What is MVC and how does it work in Android?
What is MVP and how is it different from MVC?
What is the Repository pattern?
What is the SingleLiveEvent problem?
What is separation of concerns and how do architecture patterns enforce it?
How does the ViewModel communicate with the View in different patterns?
What is a reducer in MVI?
How do you handle side effects in MVI?
When would you choose MVI over MVVM?
How do you test a ViewModel?
What are common mistakes when implementing MVVM?
What is the role of the domain layer in Clean Architecture?

Dependency Injection — Hilt, Dagger, Koin

What is Dependency Injection and why do I need it?
What is the difference between Service Locator and Dependency Injection?
What is Dagger 2 and how does it work?
What is Hilt and how is it different from Dagger?
What is the difference between @Provides and @Binds?
What are the main Hilt annotations?
What are Hilt components and their scopes?
What is Koin and how does it work?
What is the difference between compile-time and runtime DI?
How does scoping work and what happens if I get it wrong?
How does Hilt handle ViewModel injection internally?
What is @EntryPoint and when do I need it?
What is AssistedInject and when do I use it?
How do I test with Hilt?
What are Dagger Components and Subcomponents?
How do I do manual DI without a framework?
How does DI work in a multi-module project?

Modularization & Multi-Module

What is modularization and why do I modularize?
What are the common types of modules?
What is the difference between feature-based and layer-based modularization?
What does the dependency graph look like?
What is the difference between api and implementation in Gradle?
How do I handle navigation between feature modules?
How do I avoid circular dependencies?
What are the build time benefits?
How does Hilt work across modules?
What are Gradle convention plugins?
How do I enforce module boundaries?
How do I share data across feature modules?
How do I decide the right granularity?
What are dynamic feature modules?
How do I structure shared resources?
What is the impact on testing?
How do I migrate a monolithic app to multi-module?

Design Patterns in Android

What is the Observer pattern and how does Android use it?
What is the Singleton pattern and how is it used in Android?
What is the Builder pattern and where do you see it in Android?
What is the Factory pattern?
What is the Repository pattern and why is it central to Android architecture?
What is the Strategy pattern?
What is the Adapter pattern?
What is the Decorator pattern?
What is the Facade pattern?
What is the Command pattern and where does Android use it?
How does the Observer pattern differ between LiveData and Flow?
How does the Android SDK use design patterns internally?
When should you prefer composition over inheritance to apply design patterns?
How do you decide which design pattern to use in a real Android project?
What is the difference between the Template Method pattern and Strategy pattern?

Error Handling & Resilience

How do you model errors using sealed classes?
What is the difference between exceptions and errors in Kotlin?
What is Kotlin’s built-in Result type?
How does try-catch work with coroutines?
What is CoroutineExceptionHandler?
How do you handle errors in Flow chains?
How do you design error states in a ViewModel using UDF?
How do you map network errors to user-facing messages?
How do you handle timeout in coroutines?
What is the difference between Result type and sealed class error modeling?
What is exponential backoff and when do you use it?
What is the circuit breaker pattern?
How do you implement graceful degradation in an Android app?
How do you handle global error handling and crash reporting?

Testing Strategy & Testable Code

What is the test pyramid and why does it matter?
What makes code testable?
What are the different types of test doubles?
How do you write unit tests with JUnit and MockK?
What is the difference between Mockito and MockK?
What is the role of dependency injection in writing testable code?
How do you test coroutines with TestDispatcher?
How do you test a ViewModel that uses SavedStateHandle?
How do you test Flows?
How do you test Compose UI?
How does Robolectric work and when should you use it?
What is Espresso and how does it differ from Compose testing?
How do you structure tests for a Clean Architecture app?
How do you handle flaky tests?
What is code coverage and how much should you aim for?

Android Libraries

Networking — OkHttp & Retrofit

What is an OkHttp Interceptor? What is the difference between an application interceptor and a network interceptor?
How does HTTP caching work in OkHttp?
How do you enable logging in OkHttp?
What is connection pooling and how does OkHttp manage it?
How does Retrofit integrate with Kotlin Coroutines and Flow?
What is a Multipart request and how do you implement it with Retrofit?
How does Retrofit’s converter system work? How do you add custom converters?
How would you implement retry logic with OkHttp?

Image Loading — Glide & Coil

How does an image loading library like Glide or Coil work internally?
What is a Bitmap Pool and how does it improve performance?
What is the difference between Glide and Coil?
How does Coil integrate with Jetpack Compose?
What caching layers does Glide/Coil use (memory cache, disk cache)?
How do you handle image loading in a RecyclerView with large lists?
How do you load images with custom transformations (rounded corners, blur)?
What design patterns does Glide use internally?

Dependency Injection — Hilt & Dagger

What is the difference between Dagger 2 and Hilt?
How do @Inject, @Module, @Provides, @Component, and @Singleton work in Dagger?
What are custom scopes in Dagger and when do you need them?
How does Hilt simplify ViewModel injection compared to Dagger?
What is the difference between @ActivityRetainedScoped and @ViewModelScoped in Hilt?
How does Hilt handle multi-module projects?
What are @EntryPoint and @InstallIn and when do you use them?
How would you migrate from Dagger to Hilt?

RxJava

What is RxJava and how does it differ from Kotlin Coroutines?
What is the difference between Observable, Single, Completable, Maybe, and Flowable?
What is the difference between map and flatMap in RxJava?
What are Subjects in RxJava? Explain PublishSubject, BehaviorSubject, and ReplaySubject.
What are Schedulers in RxJava? What is the difference between Schedulers.io() and Schedulers.computation()?
What is CompositeDisposable and when should you call dispose() vs clear()?
How do you handle errors in RxJava?
How do you make two parallel network calls using RxJava Zip operator?
What is the difference between Concat and Merge operators?
When would you still use RxJava over Kotlin Coroutines in a modern Android project?

Firebase

How does Firebase Cloud Messaging (FCM) work end-to-end?
What is Firebase Remote Config and how do you use it for feature flags?
How does Firebase Crashlytics capture and report crashes?
What is Firebase App Distribution and when is it used?

Java

SOLID Principles

What is the Single Responsibility Principle (SRP) and how does it apply to Android?
What is the Open/Closed Principle (OCP)? Give an Android example.
What is the Liskov Substitution Principle (LSP) and where can it be violated?
What is the Interface Segregation Principle (ISP) and why does it matter?
What is the Dependency Inversion Principle (DIP)? How does it relate to Dependency Injection?

OOP Concepts

Explain the four pillars of OOP: Encapsulation, Abstraction, Inheritance, Polymorphism.
What is the difference between an abstract class and an interface?
What is the difference between method overloading and method overriding?
What are the four access modifiers in Java? What does each one allow?
Can an interface implement another interface?
What is Polymorphism and how is it achieved in Java?
What is the difference between compile-time (static) and runtime (dynamic) polymorphism?
Explain the concept of String Pool in Java.
What is Serialization and Deserialization? How do you implement it?

Collections & Generics

What is the difference between Array and ArrayList?
What is the difference between HashSet and TreeSet?
What is the difference between HashMap and HashSet?
What is the difference between HashMap, LinkedHashMap, and TreeMap?
Explain Generics in Java. What is the difference between <T>, <? extends T>, and <? super T>?
What is the difference between fail-fast and fail-safe iterators?
What is ConcurrentModificationException and how do you avoid it?
What is the difference between Collections.synchronizedList and CopyOnWriteArrayList?

Objects & Primitives

How is String implemented in Java? Why is it immutable?
What is the difference between String, StringBuffer, and StringBuilder?
What are the 8 primitive types in Java?
What is the difference between int and Integer? What is autoboxing?
Do objects get passed by value or by reference in Java?
What is the contract between equals() and hashCode()?
What is a Shallow Copy vs a Deep Copy?
What is the transient modifier used for?
What are anonymous classes?
When would you make a field final?

Memory Model & Garbage Collector

How does the Java Garbage Collector work?
What are the different types of references in Java — Strong, Soft, Weak, and Phantom?
What is a memory leak in Java and how can it happen?
What is the difference between the Stack and Heap memory in Java?
What is the PermGen/Metaspace area?

Concurrency

What does the synchronized keyword mean in Java?
What is the difference between Object-Level Lock and Class-Level Lock?
What is the volatile keyword and when do you use it?
What is a ThreadPoolExecutor? What are its key parameters?
What is the difference between Concurrency and Parallelism?
What methods does the atomic package expose (get, set, compareAndSet, etc.)?
What is a deadlock? How do you prevent it?
What is the difference between wait(), notify(), and notifyAll()?

Exceptions

How do try, catch, and finally work? Does finally always run?
What is the difference between a Checked and an Unchecked Exception?
What is the difference between throw and throws?
What is a StackOverflowError and when does it occur?

Data Structures & Algorithms

Arrays, Strings & Hash Maps

Given an unsorted array, find two numbers that add up to a target (Two Sum).
What is the two-pointer technique and when do you use it?
Find the longest substring without repeating characters.
Explain Kadane’s algorithm for maximum subarray sum.
How do you check if two strings are anagrams?
How do you compute product of array except self without using division?
What is the sliding window technique?
How do you group anagrams from a list of strings?
How do you find the first non-repeating character in a string?
How do you check if a string is a palindrome?
How do you find the container with most water?
How do you find the longest palindromic substring?
Explain the “subarray sum equals k” problem.
How do you merge two sorted arrays into one sorted array?
How do you rotate an array by k positions to the right?
How do you find the minimum window substring containing all characters of a target?
How do you solve the 3Sum problem?
What’s the difference between HashMap and HashSet, and when do you use each?
What is a prefix sum and when is it useful?
How do you find all anagrams of a pattern in a string?

Linked Lists

How do you reverse a singly linked list?
How do you detect a cycle in a linked list?
How do you merge two sorted linked lists?
How do you find the middle element of a linked list?
What is a linked list and how does it differ from an array?
How do you remove the nth node from the end of a linked list?
How do you find the starting node of a cycle in a linked list?
How do you check if a linked list is a palindrome?
How do you add two numbers represented as linked lists?
How do you find the intersection point of two linked lists?
What’s the difference between singly and doubly linked lists?
Explain how an LRU Cache works using a doubly linked list and HashMap.
How do you deep copy a linked list with random pointers?
How do you reverse nodes in k-group?
How do you sort a linked list in O(n log n) time?

Stacks & Queues

How do you check if a string of parentheses is valid?
How do you design a Min Stack that supports getMin in O(1)?
What is a monotonic stack and how does it solve “next greater element”?
How do you find the largest rectangle in a histogram?
What is a stack and what are its core operations?
What is a queue and how does it differ from a stack?
How do you solve Daily Temperatures using a monotonic stack?
How do you evaluate a Reverse Polish Notation expression?
How do you implement a queue using two stacks?
How do you solve the Sliding Window Maximum problem?
What is a deque and when would you use one?
What is a priority queue and how does it differ from a regular queue?
How do you find the Kth largest element using a min-heap?
How do you merge K sorted lists using a priority queue?
When would you choose a stack over a queue?

Trees & Binary Search Trees

What is the maximum depth of a binary tree and how do you find it?
How do you invert a binary tree?
How do you validate whether a binary tree is a valid BST?
How do you find the lowest common ancestor (LCA) of two nodes in a binary tree?
How do you perform a level-order traversal (BFS) of a binary tree?
Explain the four standard tree traversals.
How do you find the diameter of a binary tree?
How do you serialize and deserialize a binary tree?
What is a binary tree and how is it represented?
How do you delete a node from a BST?
How do you find the LCA in a BST specifically?
How do you construct a binary tree from in-order and pre-order traversals?
How do you check if a binary tree is symmetric?
How do you check if a binary tree has a path with a given sum?
What is a balanced binary tree and how do AVL trees maintain balance?
How do you find all root-to-leaf paths?

Tries & Advanced Trees

What is a Trie and why use it over a HashMap for prefix-based lookups?
How do you implement insert and search in a Trie?
How does startsWith differ from search in a Trie?
How do you solve Word Search II (finding multiple words in a grid)?
How would you implement autocomplete using a Trie?
How do you delete a word from a Trie?
What is the space optimization for Tries when the alphabet is large?
What is a Segment Tree and what problem does it solve?
How do you implement a Segment Tree for range sum queries?
What is a Fenwick Tree and how does it compare to a Segment Tree?
What is an N-ary tree and how does traversal differ?
What is lazy propagation in a Segment Tree?
How would you count the number of distinct words in a Trie?

Graphs: BFS, DFS & Traversals

How do you solve the Number of Islands problem?
How does BFS work and when do you use it?
How does DFS work and when do you use it?
How do you solve the Course Schedule problem?
What is the difference between BFS and DFS?
What is topological sort and when is it used?
How do you implement topological sort using Kahn’s algorithm?
How do you detect a cycle in a directed graph?
How do you detect a cycle in an undirected graph?
What are the main ways to represent a graph?
How do you solve the Word Ladder problem?
How do you clone a graph?
How do you check if a graph is bipartite?
How do you find connected components in an undirected graph?

Graphs: Shortest Path & Advanced

What is Dijkstra’s algorithm and when do you use it?
Why does Dijkstra fail with negative edge weights?
What is Union-Find (Disjoint Set Union)?
How do you solve Cheapest Flights Within K Stops?
What is the Bellman-Ford algorithm?
How do you decide which shortest path algorithm to use?
What is a Minimum Spanning Tree?
Explain Kruskal’s algorithm and how it uses Union-Find.
Explain Prim’s algorithm for MST.
How do you solve the Network Delay Time problem?
What are common problems where Union-Find is the right tool?
What is the Floyd-Warshall algorithm?
When would you use Prim’s vs Kruskal’s?
How do you find the shortest path with 0 and 1 edge weights?
How do you detect a negative-weight cycle?

Heaps, Priority Queues & Intervals

How does a binary heap work?
How do you find the Kth largest element using a heap?
How do you merge K sorted lists?
How do you merge overlapping intervals?
How do you solve Meeting Rooms II (minimum rooms needed)?
How do you find the median from a data stream?
How do you insert a new interval into a sorted non-overlapping list?
What is the difference between a min-heap and a max-heap?
How do you build a heap from an array and why is it O(n)?
How do you solve Top K Frequent Elements?
How do you remove covered intervals?
What is a non-overlapping interval count problem?
How do you check if a person can attend all meetings?
How do you find the Kth smallest element in a sorted matrix?
What is a heap sort and how does it work?

Sorting, Searching & Binary Search

Explain standard binary search and its common pitfalls.
How do you search in a rotated sorted array?
Implement merge sort.
Implement quick sort and explain the partition step.
What is the time complexity of common sorting algorithms?
How do you find the peak element in an array?
What is the Quickselect algorithm for finding the kth largest?
How do you solve the merge intervals problem?
What is lower bound and upper bound in binary search?
How do you find the minimum in a rotated sorted array?
How does binary search apply beyond sorted arrays?
What is the difference between comparison-based and non-comparison-based sorting?
Explain stability in sorting and why it matters.
How do you solve Meeting Rooms II?
When should you implement sorting from scratch vs using built-in sort?

Dynamic Programming Fundamentals

How do you solve the Climbing Stairs problem?
How do you solve the Coin Change problem?
What is dynamic programming and when do you use it?
What is the difference between memoization and tabulation?
How do you solve the House Robber problem?
How do you find the Longest Increasing Subsequence (LIS)?
How do you solve the 0/1 Knapsack problem?
How do you solve Edit Distance?
How do you find the Longest Common Subsequence (LCS)?
How do you solve Unique Paths on a grid?
How do you solve the Word Break problem?
How do you solve the Decode Ways problem?
How do you solve the Minimum Path Sum problem?
How do you identify whether a problem is a DP problem?
How do you convert recursive to bottom-up DP?
How do you optimize 2D DP space?

Dynamic Programming Advanced

How do you solve Best Time to Buy and Sell Stock (one transaction)?
How do you solve Buy and Sell Stock with unlimited transactions?
What is state machine DP?
How do you solve Buy and Sell Stock with cooldown?
How do you solve Buy and Sell Stock with at most k transactions?
How do you solve the Longest Palindromic Subsequence?
What is interval DP?
How do you solve Burst Balloons?
What is bitmask DP and when do you use it?
How do you solve Regular Expression Matching?
How do you solve Matrix Chain Multiplication?
How do you solve Palindrome Partitioning II (minimum cuts)?
What is tree DP?
How do you solve Interleaving String?
How do you approach DP on strings?

Recursion, Backtracking & Greedy

How do you generate all permutations of an array?
How do you generate all subsets of an array?
What is backtracking and how does it differ from brute force?
How do you solve the N-Queens problem?
How do you solve the Jump Game problem?
What is a greedy algorithm?
What is recursion and what are its essential parts?
How does the call stack work during recursion?
How do you solve Word Search on a board?
How do you solve the Gas Station problem?
How do you solve Partition Labels?
How do you generate combinations of k elements from n?
How do you handle duplicates in subsets and combinations?
When does greedy work and when does it fail?
How does the Activity Selection problem demonstrate greedy?

Bit Manipulation & Math

How does XOR help find a single number where every other number appears twice?
How do you check if a number is a power of two?
How do you count the number of 1 bits (Hamming weight)?
How do you find the missing number in an array of 0 to n?
What are the basic bitwise operators?
How do you check, set, clear, and toggle a specific bit?
How do you find two non-repeating numbers where every other appears twice?
How do you count total 1 bits for every number from 0 to n?
What is bit masking for representing subsets?
How do you compute GCD using Euclid’s algorithm?
How does the Sieve of Eratosthenes work?
How do you reverse the bits of a 32-bit integer?
How do you find the Hamming distance between two integers?
How do you add two integers without + or - operators?
How do you compute a^b mod m efficiently?
What is modular arithmetic and why does it matter?
How do you solve “single number” when one number appears once and others appear three times?

System-Oriented DSA & Mobile Specific

How do you implement an LRU Cache with O(1) get and put?
How does an LFU Cache differ from LRU?
How do you design a HashMap from scratch?
How do you implement a Trie-based autocomplete system?
How do you design a Twitter/News Feed system using DSA?
How do you implement a stack that supports push, pop, and getMin in O(1)?
How do you design a data structure for insert, remove, and getRandom in O(1)?
How would you implement a time-based key-value store?
How do you implement a basic rate limiter using a queue?
How do you merge K sorted arrays?
How do you solve the task scheduler problem?

Mobile System Design

Fundamentals of Mobile System Design

How do you structure the high-level architecture of a mobile app?
What is the single source of truth pattern and why does it matter?
How do you choose an architecture pattern (MVVM, MVI) and set up dependency injection?
How do you design caching in detail?
How do you handle threading and concurrency?
How do you design offline support?
How do you decide on client-server communication?
How do you design the API contract from the mobile client’s perspective?
How do you design the data model?
How do you implement pagination on the client?
What’s the first thing you should do when given a mobile system design problem?
How do you identify functional requirements for a mobile system design?
How do you identify non-functional requirements?
How do you define scope and resource constraints?
How do you address non-functional requirements in the high-level design?
How do you approach performance in a system design answer?
How do you handle accessibility and localization?
How do you address security concerns?

Design: Chat Application

How would you layer the client architecture for a chat app?
Why WebSocket over long polling or SSE for real-time messaging?
What data model would you use for messages?
How does the offline message queue work?
How do you handle message ordering? What problems can arise?
How do you handle retry logic and delivery guarantees?
How do you manage the WebSocket connection lifecycle?
How do you structure the local Room database schema?
What are the core features you would include in a chat application?
What are the key non-functional requirements for a chat app?
What’s in scope and what’s out of scope for a mobile system design interview?
What does the API design look like for conversations and messages?
How do push notifications work for a chat app?
How do you sync message history after the app has been offline?
How do you implement read receipts?
How do you implement typing indicators?
How do you handle media messages like images and videos?
How do you make the chat list screen performant?
How would you implement message search?
How does end-to-end encryption work at a high level?
How does group messaging differ from 1:1 chats?

What are the core features of a social media feed?
What are the non-functional requirements?
What’s in scope and what’s out of scope for this design?
What does the client architecture look like?
How do you design the API for feed pagination?
How do you model a feed item that supports multiple content types?
What caching strategy works best for a feed?
How do you handle image loading in the feed?
How do you handle pull-to-refresh and real-time updates?
How do you optimize RecyclerView or LazyColumn performance for a feed?
How does prefetching work for both data and images?
How do you implement optimistic UI for the like button?
How would you handle video autoplay in the feed?
How do you handle multiple view types in a feed?
How do you handle offline caching with TTL?
How do you track analytics events in a feed?
How do you deep link to a specific post in the feed?
How do you make the feed accessible?

Design: Image Loading Library

What does the overall loading pipeline look like?
How does the memory cache work?
How does the disk cache work?
How do you handle lifecycle awareness?
What is bitmap pooling and why is it important?
How would you downsample images to avoid OutOfMemoryError?
What’s the threading strategy?
What are the core responsibilities of an image loading library?
How would you design the public API?
What platforms and use cases should the library support?
How do you generate cache keys?
How do you handle placeholder and error images?
What is request deduplication and how would you implement it?
How do you handle image transformations?
How do you respond to memory pressure?
How do you handle disk cache eviction?
How would you implement a priority system for image loads?
How do Coil and Glide differ in their architecture?

Design: File Downloader Library

What are the core functional requirements for a file downloader library?
What would you keep out of scope for an initial design?
What are the main components in the architecture?
What does the data model look like for a download task?
How do HTTP Range requests enable resume?
What states can a download be in, and how do transitions work?
How does notification integration work?
Walk through the pause/resume implementation in detail.
How do you manage concurrent downloads?
How do you implement progress tracking without flooding the UI?
How should background downloads work on Android?
What disk I/O strategy should you use?
How do you verify file integrity after download?
How do you handle retry on network failure?
How does the priority queue work?
How would you test a file downloader library?

Design: Networking Library

What are the core functional requirements?
What is in scope and what is out of scope?
What does the high-level architecture look like?
How does the interceptor chain pattern work?
How does the serialization layer work?
How does connection pooling work at a high level?
How does HTTP caching work?
How would you implement the interceptor chain internally?
How do connection pooling and keep-alive work internally?
How does TLS and certificate pinning work?
How do you implement request cancellation and timeouts?
How does retry with exponential backoff work?
How do multipart uploads work?
How do you handle response streaming for large files?
How do thread safety and the dispatcher work?
How would you test a networking library?

Design: Video Streaming App

What are the core functional requirements for a video streaming app?
What are the key non-functional requirements?
What would you keep out of scope for a 45-minute design session?
How would you structure the client architecture?
Why ExoPlayer / Media3 as the playback engine?
What APIs does the client need from the backend?
What data models would you use on the client?
How would you design the caching strategy?
How does video delivery work with a CDN?
How does adaptive bitrate streaming work on mobile?
How would you configure the buffering strategy?
How would you implement background playback with MediaSession?
How would you implement offline downloads?
How does DRM (Widevine) work on Android?
How would you implement picture-in-picture mode?
How would you support Chromecast?
How would you handle video preloading in a scrollable list?
How would you optimize for performance and battery life?

Design: Music Streaming App

What are the core features of a music streaming app?
How would you scope this for a 45-minute interview?
Why use Media3/ExoPlayer for audio playback?
What APIs does the app need from the backend?
What are the core data models?
How do you keep music playing in the background?
How does audio focus work in a music app?
How would you implement gapless and crossfade playback?
How would you handle offline downloads?
How would you design the playback queue?
How do MediaSession and media controls work together?
How would you handle audio streaming and buffering?
How would you implement an equalizer and audio effects?
How would you handle Bluetooth, Cast, and car integration?
How would you handle search and recommendation on the client?

Design: eCommerce App

What are the core functional requirements for an e-commerce app?
What is out of scope for a typical interview?
What API endpoints does the client need?
What caching strategy would you use?
How would you handle image loading in a product grid?
How would you design search with filters and sorting?
How would you optimize product listing performance?
How would you design cart management — local vs server sync?
How would you design the checkout flow with payment integration?
How do you handle idempotency in checkout?
How would you design order tracking with real-time updates?
How would you handle push notifications for deals and delivery updates?
How would you implement deep linking to a product page?
How would you A/B test product layouts?
How would you handle offline catalog browsing?
How would you handle security — payment tokenization and certificate pinning?

What are the core features a ride-sharing app needs?
Should the rider and driver be the same app or separate apps?
How does real-time communication work?
What API endpoints does the ride lifecycle need?
What data models does the client need?
How does map integration work?
How does the ride state machine work?
How does location tracking work under the hood?
How do you animate the driver marker smoothly on the map?
How do you optimize map rendering performance?
How does ETA calculation work?
How do you handle offline or poor connectivity during an active ride?
How do you display surge pricing to the rider?
What does the fare estimation flow look like?
How does background location work during a ride?
How does driver matching look from the client side?
How would you abstract the map SDK so you could swap Google Maps for Mapbox?

What are the core functional requirements for a location sharing app?
How would you scope the design for a 45-minute interview?
How does real-time location sharing work?
What APIs does the client need?
What are the key data models?
How do you integrate a map SDK?
How does the location provider strategy work?
How do you track location without killing the battery?
How do you implement geofencing?
How do you handle map rendering performance?
How do you support offline maps?
How does background location work on modern Android?
How do you implement privacy controls for location sharing?
How do you handle real-time updates at scale?
How do you filter noisy location data?
How do you test location features?

Design: File Sync App

What core features should a file sync app support on the client side?
What should we exclude from scope for this interview?
How does delta sync work with version vectors?
How should the local file storage be structured?
How would the sync engine coordinate everything?
How would you implement chunked uploads with resume on failure?
How does chunked download with resume work?
How would you handle conflict resolution?
How should background sync be scheduled?
How would you detect local file changes?
How would you optimize bandwidth usage?
How should offline editing work?
How should files be encrypted at rest and in transit?
How would you implement selective sync?
How would you handle very large files without running out of memory?

Design: Offline-First Application

What does “offline-first” actually mean? How is it different from just caching?
What are the functional requirements for an offline-first app?
What non-functional requirements matter most?
How would you architect an offline-first app at a high level?
Why use the local database as the source of truth instead of the server?
How would you design the data model with sync metadata?
How would you design the pending operations queue?
How would you design the API for delta sync?
How do you detect conflicts during sync?
What are the main conflict resolution strategies?
How would you implement field-level merge?
How do you compact the pending operations queue before syncing?
How do you use WorkManager for background sync?
How do you monitor network state and trigger sync on reconnect?
How do you handle schema migrations when users have unsynced data?
How do you implement optimistic UI with rollback?
How do you test offline scenarios?
How do you handle large file sync like images or documents?

Design: Analytics & Crash Reporting SDK

What are the core functional requirements for an analytics and crash reporting SDK?
Where does the SDK’s responsibility end and the host app’s begin?
What does the overall SDK architecture look like?
What does the backend ingestion endpoint look like?
What do the data models look like?
How does the batching strategy work?
How should initialization and configuration work?
How would you capture crashes?
How does the ANR watchdog work internally?
How would you implement the event batching and flush logic?
How would you design local storage for pending events?
How would you handle reliable delivery with retries?
How would you handle privacy and consent?
How would you minimize performance impact on the host app?
How does session tracking work?
How would you handle disk and memory limits?
How would you test an analytics SDK?

Behavioral & Career

STAR Method & Common Questions

What is the STAR method and how do you use it in interviews?
How do you answer “Tell me about yourself”?
How do you answer “What are your strengths”?
How do you answer “What are your weaknesses”?
How do you handle deadline pressure?
How do you answer “What has been your biggest challenge”?
How do you answer “Tell me about a conflict with a teammate”?
How do you talk about handling failure?
Tell me about a time you mentored someone.
Describe a time you disagreed with your manager.
Tell me about a time you went above and beyond.
How do you prioritize when you have multiple competing demands?
Tell me about a time you made a decision with incomplete information.
How do you give feedback during code reviews?
Describe a situation where you received critical feedback.
Tell me about a time you pushed back on a product requirement.
Tell me about a project where things didn’t go as planned.

Career Growth, Failure & Salary Negotiation

Walk me through your career trajectory.
What’s your biggest professional failure and what did you learn?
What are your strengths?
What are your weaknesses?
Where do you see yourself in 5 years?
Why do you want to work at this company?
Why are you leaving your current role?
How do you approach salary negotiation?
How do you evaluate a job offer beyond salary?
How do you handle a counter offer from your current employer?
Tell me about a time you failed at something significant. How did you recover?
How do you stay current with technology?
How do you handle imposter syndrome?
Tell me about a production incident you caused. What happened and what changed?
How do you talk about gaps in your resume?
What questions should you ask the interviewer?
How do you handle burnout?

Leadership, Ownership & Technical Decisions

What does technical leadership look like without a management title?
What does it mean to own a feature end-to-end?
How do you handle ambiguity in requirements?
How do you approach making a trade-off between speed and quality?
How do you decide whether to refactor or ship?
Tell me about a time you influenced a decision without having authority.
Describe a time you drove a significant technical decision. How did you get buy-in?
How do you choose between two libraries or frameworks when both seem viable?
Tell me about a time you made a technical decision that turned out to be wrong. What did you do?
How do you approach a large, ambiguous project with no clear solution?
How do you manage stakeholders who have conflicting priorities?
Tell me about a time you took ownership of something outside your job description.
How do you approach architecture decisions for a feature that needs to scale?
Describe a time you had to balance technical debt with feature delivery.
How do you make decisions when your team is split on an approach?
Tell me about a time you had to say no to a stakeholder.
How do you evaluate whether a new technology is worth adopting?

Agile, Scrum & Team Collaboration

What is Agile and why do teams use it?
What is Scrum and how does it differ from Agile?
What happens in each Scrum ceremony?
What are story points and how do you estimate work?
What is sprint velocity and how is it used?
What is the Definition of Done?
How do you give effective feedback in code reviews?
How do you receive feedback on your own code?
How do you collaborate with product managers who don’t have technical context?
How do you handle a blocker that’s outside your control?
How does your team handle knowledge sharing?
How do you work effectively in a remote or distributed team?
What makes a good sprint retrospective?
How do you handle scope creep during a sprint?
How do you estimate work when requirements are unclear?
What’s your approach to working with designers?

Coding Tests

What Companies Expect

What are the common coding test formats?
What do evaluators look for in a submission?
What should a good README contain?
How important is Git history?
How should I structure a coding test project?
Should I use Jetpack Compose or XML Views?
What are the most common mistakes in coding tests?
How should I handle ambiguous requirements?
How should I manage time in a timed take-home test?
What does good architecture look like for a small coding test app?
How should I implement error handling?
What level of testing is expected?
How do I handle API keys securely?
How should I approach a live coding interview vs a take-home test?
What should I do if I can’t finish the coding test in time?
What differentiates a good submission from a great one?
How do I decide what to include and what to skip when time is limited?

Machine Coding Round

What is a machine coding round and how does it differ from a take-home assignment?
What are the common formats?
What do evaluators actually watch for?
What architecture should I default to?
How should I spend the first 10-15 minutes?
What’s a good time management strategy for a 90-minute round?
How do I handle API calls in a timed round?
How do I display a list quickly in Compose?
How do I deal with ambiguous requirements?
What patterns should I have memorized?
How do I add error handling quickly?
What should I NOT do in a machine coding round?
How do I write a quick unit test when time is short?
How do I handle the last 10 minutes?
What separates a strong submission from an average one?

Build: Todo App

How do you set up Room for a notes app?
How do you display notes in a LazyColumn?
How do you implement swipe-to-delete?
How do you implement undo delete with a Snackbar?
How do you build the add/edit note screen with form validation?
How do you implement search and filter for notes?
How do you implement sorting by date or priority?
How do you structure clean architecture for a notes app?
How do you set up Hilt for dependency injection?
How do you handle offline-first architecture in a notes app?
How do you support dark mode?
How do you unit test the ViewModel?
How do you write UI tests for the notes app?
Why is the to-do app a good test of fundamentals?
How do you handle the back press when editing a note with unsaved changes?

Build: Weather App

How do you set up Retrofit for API integration?
How do you parse JSON responses into Kotlin data classes?
How do you implement loading, error, and success states?
How do you handle network errors properly?
How do you structure MVVM for a weather/news feature?
How do you implement search functionality?
How do you implement pull-to-refresh?
How do you implement offline caching with Room?
How do you handle the separation between DTOs, entities, and domain models?
How do you handle empty states in a list-based app?
How do you unit test the repository layer?
How do you structure the data layer to make it testable?
How do you decide between StateFlow and LiveData for UI state?
What’s the difference between Retrofit and Ktor for API integration?
How do you handle configuration changes without losing UI state?

Build: Movie Listing

What is the master-detail pattern and why is it common in coding tests?
How do you build a scrollable list using LazyColumn in Compose?
How do you build the same list using RecyclerView?
How do you handle navigation from the list screen to the detail screen?
How do you load images with Coil in a list?
How do you structure the data layer for a list-detail feature?
How should the detail screen load its data?
How do you implement infinite scroll with Paging 3?
How do you implement search and filter in a list screen?
How do you handle state preservation on configuration changes?
How do you design a clean navigation setup for a single-activity app?
What is the difference between client-side and server-side pagination?
How do you handle error states in a paged list?
How do you optimize image loading in a large list?

Build: StackOverflow Users App

How do you set up Retrofit to call the StackOverflow or GitHub API?
How do you display the fetched users or repos in a LazyColumn?
How do you handle loading, error, and empty states?
How do you display user avatars with Coil?
How do you navigate to a detail screen?
How do you implement search with debounce?
How do you structure the project packages?
How do you implement pagination with Paging 3?
How do you implement manual pagination without Paging 3?
How do you separate DTOs from domain models?
How do you cache API responses in Room for offline access?
How do you set up Hilt dependency injection for this project?
How do you handle GitHub API rate limiting?
What’s the difference between the StackOverflow and GitHub API response structures?

Build: Custom UI Component

What is the difference between invalidate() and requestLayout()?
What are the three phases of custom View rendering?
How do you implement onMeasure in a custom View?
How do you draw on a Canvas in a custom View?
How do you handle touch events in a custom View?
How do you do custom drawing in Compose?
How do you create a custom layout in Jetpack Compose?
How do you handle gestures in Compose?
How do you animate a custom drawn component?
How do you design a reusable API for a custom component?
How do you make a custom component accessible?
How do you handle intrinsic measurements in a custom Compose layout?
How do you handle pinch-to-zoom in Compose?
What are common performance pitfalls with custom drawn components?
How would you build a custom chart component for a coding test?

Code Review & Refactoring

What are code smells and how do you spot them?
How do you improve naming conventions in a codebase?
How do you reduce coupling between classes?
How do you refactor a God Activity or God ViewModel?
What does it mean to refactor toward SOLID principles?
How do you spot and remove code duplication?
How do you extract use cases from a bloated ViewModel?
How do you replace callbacks with coroutines or Flow?
How do you improve testability of existing code?
What do you look for first when reviewing unfamiliar code?
How do you approach a refactoring challenge without breaking existing behavior?
How do you spot and fix memory leaks in a code review?
How do you identify and fix performance issues in a code review?
How do you refactor error handling from scattered try-catch to a structured approach?
How do you suggest architectural improvements without rewriting everything?

900+ Android Interview Questions

Android Interview Questions

Android Platform

Activity & Fragment Lifecycle

Android Components

Intents, Launch Modes & Navigation

Views, RecyclerView & Custom UI

Threading & Background Work

Storage & Data Persistence

Networking & API Communication

Notifications, Permissions & Security

Memory Management & Performance

Gradle & Build System

Android Internals & Process Management

App Links, Deep Links & Navigation

Sensors, Camera & Hardware APIs

Accessibility & Localization

Kotlin

Basics & Type System

Functions & Scope Functions

Collections, Sequences & Functional Patterns

Generics, Variance & Reified Types

Kotlin Under the Hood

Contracts, DSLs & Advanced Patterns

Kotlin Coroutines & Flows

Coroutines Basics

Coroutines Advanced

Cold Flows & Operators

Hot Flows, StateFlow & SharedFlow

Jetpack Compose

Fundamentals & Thinking in Compose

State Management

Side Effects & Lifecycle

Recomposition, Stability & Performance

Layouts, Modifiers & Custom Drawing

Animation APIs

Navigation, Theming & Architecture

Testing & Accessibility

Architecture & Design

Clean Architecture & SOLID Principles

MVVM, MVI & Architecture Patterns

Dependency Injection — Hilt, Dagger, Koin

Modularization & Multi-Module

Design Patterns in Android

Error Handling & Resilience

Testing Strategy & Testable Code

Android Libraries

Networking — OkHttp & Retrofit

Image Loading — Glide & Coil

Dependency Injection — Hilt & Dagger

RxJava

Firebase

Java

SOLID Principles

OOP Concepts

Collections & Generics

Objects & Primitives

Memory Model & Garbage Collector

Concurrency

Exceptions

Other Java Topics

Data Structures & Algorithms

Arrays, Strings & Hash Maps

Linked Lists

Stacks & Queues

Trees & Binary Search Trees

Tries & Advanced Trees

Graphs: BFS, DFS & Traversals

Graphs: Shortest Path & Advanced

Heaps, Priority Queues & Intervals

Sorting, Searching & Binary Search

Dynamic Programming Fundamentals

Dynamic Programming Advanced

Recursion, Backtracking & Greedy

Bit Manipulation & Math

System-Oriented DSA & Mobile Specific

Mobile System Design

Fundamentals of Mobile System Design

Design: Chat Application

Design: News Feed & Social Media