Android Interview Questions and Answers (Complete Guide) - Part-2

Section 12: Senior Android Questions

55. Explain Modularization.

Benefits:

• Faster builds
• Reusability
• Independent teams

Example:

app
core
network
feature-home
feature-profile

56. How do you reduce APK size?

Answer:

• R8
• Proguard
• App Bundles
• Image compression
• Remove unused resources

57. How do you optimize app performance?

• Lazy loading
• Paging
• Memory optimization
• Avoid memory leaks
• Baseline profiles

58. Explain Memory Leak.

Example:

object Singleton {
   var activity: Activity? = null
}

Activity never released.

59. How to detect memory leaks?

Tools:

• LeakCanary
• Android Profiler

60. Difference between ANR and Crash

Section 13: Android System Design (Lead/Architect)

61. Design WhatsApp Chat Module

Discuss:

• Offline first
• Room cache
• Paging
• WebSocket
• Push notifications

62. Design YouTube Feed

Topics:

• Pagination
• Caching
• Video preloading
• Analytics

63. Design Uber Driver Tracking

Topics:

• Real-time location
• Maps
• Background service
• Battery optimization

64. How would you architect a large-scale Android application?

Answer:

Presentation
   ↓
Domain
   ↓
Data

Use:

• Clean Architecture
• MVVM
• Hilt
• Coroutines
• Modularization

65. Explain Clean Architecture

UI Layer
  ↓
Domain Layer
  ↓
Data Layer

Benefits:

• Scalability
• Maintainability
• Testability

Advanced Android Interview Questions & Answers

66. What is the difference between Serializable and Parcelable?

• Serializable

class User(
   val id: Int,
   val name: String
) : Serializable

Advantages

• Easy to implement
• Java standard

Disadvantages

• Slow
• Uses Reflection
• More memory consumption

• Parcelable

@Parcelize
data class User(
   val id: Int,
   val name: String
) : Parcelable

Advantages

• Faster
• Android optimized
• Better performance

Disadvantages

• More code without Parcelize

67. What is IPC in Android?

IPC stands for Inter Process Communication.

Used when:

• One app communicates with another
• Bound services
• AIDL implementation

Example:

App A
 ↕
Binder
 ↕
App B

68. What is AIDL?

Android Interface Definition Language.

Used for communication between different processes.

Example:

interface IUserService {
   String getUserName();
}

Used in:

• Banking apps
• Enterprise apps
• Background services

69. What is Binder?

Binder is Android's IPC mechanism.

Flow:

Client
  ↓
Binder
  ↓
Service

Most Android framework services use Binder internally.

70. What happens when screen rotation occurs?

Before ViewModel:

Activity Destroyed
↓
Activity Recreated

Lifecycle:

onPause()
onStop()
onDestroy()

onCreate()
onStart()
onResume()

71. How does ViewModel survive configuration changes?

ViewModel is stored inside:

ViewModelStore

When Activity recreates:

Old Activity Destroyed
↓
ViewModel Retained
↓
New Activity Attached

Example:

class UserViewModel : ViewModel()

72. What is SavedStateHandle?

Used to restore state after process death.

Example:

class UserViewModel(
   private val state: SavedStateHandle
) : ViewModel()

Save:

state["userId"] = 10

Retrieve:

val userId = state["userId"]

73. What is Process Death?

Occurs when Android kills app process.

Reasons:

• Low memory
• Background restrictions
• System resource optimization

74. Configuration Change vs Process Death

75. What is WorkManager?

Recommended API for deferrable background work.

Example:

class SyncWorker(
   context: Context,
   params: WorkerParameters
) : Worker(context, params) {

   override fun doWork(): Result {
       return Result.success()
   }
}

76. Why WorkManager instead of Service?

77. Types of WorkManager Requests

One Time

OneTimeWorkRequestBuilder<SyncWorker>()

Periodic

PeriodicWorkRequestBuilder<SyncWorker>()

78. Explain Dependency Injection.

Without DI:

class UserRepository {
   private val api = ApiService()
}

Tightly coupled.

With DI:

class UserRepository(
   private val api: ApiService
)

Benefits:

• Testability
• Scalability
• Loose coupling

79. What is Constructor Injection?

class UserRepository @Inject constructor(
   private val api: ApiService
)

Recommended by Hilt.

80. What is Field Injection?

@Inject
lateinit var repository: UserRepository

Single instance across application.

82. What is Scoped Dependency?

Example:

@ActivityRetainedScoped
class UserRepository

Instance exists only for specific scope.

83. Explain SOLID Principles.

S - Single Responsibility

One class should have one responsibility.

Bad:

class UserManager {
   fun saveUser(){}
   fun sendEmail(){}
}

Good:

class UserRepository
class EmailService

O - Open Closed Principle

Open for extension.

Closed for modification.

L - Liskov Substitution

Child class should replace parent safely.

I - Interface Segregation

Small interfaces are better.

Bad:

interface Worker {
   fun code()
   fun cook()
}

D - Dependency Inversion

Depend on abstraction.

interface Api

Not concrete implementation.

84. Explain Clean Architecture.

Layers:

Presentation
   ↓
Domain
   ↓
Data

Presentation Layer

Contains:

• Activity
• Fragment
• Compose UI
• ViewModel

Domain Layer

Contains:

• UseCases
• Business logic

Example:

class GetUsersUseCase

Data Layer

Contains:

• Repository
• API
• Room

85. Repository Pattern

Repository acts as Single Source of Truth.

Example:

class UserRepository(
   private val api: ApiService,
   private val dao: UserDao
)

Flow:

ViewModel
↓
Repository
↓
API / DB

86. What is Single Source of Truth?

Only one component owns data.

Example:

Repository

instead of

Activity
Fragment
Repository

maintaining separate copies.

87. What is Offline First Architecture?

Flow:

UI
↓
Room
↓
Sync
↓
API

Benefits:

• Works without internet
• Faster UI
• Better UX

88. What is Paging 3?

Used for large datasets.

Example:

Pager(
   config = PagingConfig(
       pageSize = 20
   )
)

Benefits:

• Memory efficient
• Smooth scrolling

89. What is RemoteMediator?

Connects:

Network
↕
Room

for Paging 3.

Example:

class UserRemoteMediator

90. Explain StateFlow.

private val _state =
   MutableStateFlow(UiState())

Observe:

state.collect {}

Characteristics:

• Hot stream
• Always has value
• State holder

91. Explain SharedFlow.

MutableSharedFlow<Event>()

Used for:

• Navigation
• Snackbar
• One-time events

92. Why not use StateFlow for Events?

Problem:

Rotation
↓
State replayed
↓
Duplicate event

SharedFlow solves this.

93. What is Cold Flow?

Starts producing values when collected.

Example:

flow {
   emit(1)
}

94. What is Hot Flow?

Produces values regardless of collectors.

Examples:

StateFlow
SharedFlow

95. What is Backpressure?

When producer emits faster than consumer processes.

Solution:

buffer()
conflate()
collectLatest()

96. Difference Between collect and collectLatest

collect

Processes all emissions.

flow.collect {}

collectLatest

Cancels previous emission processing.

flow.collectLatest {}

Useful in search functionality.

97. Explain Mutex in Coroutines

Used to avoid race conditions.

Example:

val mutex = Mutex()

mutex.withLock {
   count++
}

98. What is SupervisorJob?

Failure of one child won't cancel others.

SupervisorJob()

99. Explain ANR.

ANR = Application Not Responding

Occurs when:

Main Thread Blocked > 5 seconds

Example:

Thread.sleep(10000)

Never perform network/database work on main thread.

100. How to Prevent ANR?

Use:

Dispatchers.IO
WorkManager
Background Threads
Coroutines

Avoid:

Heavy loops
Large DB queries
Network calls on UI thread

101. What is Choreographer?

Android component responsible for frame scheduling.

Target:

60 FPS

Frame budget:

16.67 ms

If exceeded:

Dropped Frames
↓
Jank

102. What is Jank?

UI stuttering caused by:

• Heavy recomposition
• Main thread blocking
• Large layouts
• Excessive allocations

103. How do you improve app startup time?

Techniques:

• App Startup library
• Lazy initialization
• Baseline Profiles
• Reduce dependency initialization
• SplashScreen API

104. What are Baseline Profiles?

Precompile critical code paths.

Benefits:

• Faster startup
• Faster navigation
• Better scrolling performance

105. How do you secure API keys?

Never:

const val API_KEY = "123456"

Use:

• Remote configuration
• Encrypted storage
• Backend token generation

106. What is Proguard/R8?

Used for:

• Code shrinking
• Obfuscation
• Optimization

Example:

minifyEnabled true

107. How do you secure local data?

Use:

EncryptedSharedPreferences

or

EncryptedFile

108. What is Android Keystore?

Stores encryption keys securely.

Example:

KeyGenParameterSpec.Builder(...)

109. Explain Certificate Pinning.

Prevents MITM attacks.

Implemented using:

OkHttp CertificatePinner