Android Interview Questions and Answers (Complete Guide)-Part-1

Section 1: Android Basics (Fresher Level)

1. What is Android?

Answer:
Android is an open-source mobile operating system developed by Google based on the Linux kernel.

Features:

• Open source
• Multi-touch support
• Rich application framework
• Supports Java and Kotlin
• Large ecosystem

2. What are the main components of Android?

Answer:

Android has four major application components:

1. Activity
2. Service
3. Broadcast Receiver
4. Content Provider

Example:

class MainActivity : AppCompatActivity()

Activity represents a single screen.

3. What is an Activity?

Answer:

An Activity represents a user interface screen.

Example:

class MainActivity : AppCompatActivity() {

   override fun onCreate(savedInstanceState: Bundle?) {
       super.onCreate(savedInstanceState)
       setContentView(R.layout.activity_main)
   }
}

4. Explain Activity Lifecycle.

Answer:

Lifecycle methods:

onCreate()
onStart()
onResume()
onPause()
onStop()
onDestroy()

Lifecycle flow:

onCreate
  ↓
onStart
  ↓
onResume
  ↓
Running
  ↓
onPause
  ↓
onStop
  ↓
onDestroy

5. Difference between onStart() and onResume()

6. What is Intent?

Answer:

Intent is used for communication between Android components.

Example:

val intent = Intent(this, SecondActivity::class.java)
startActivity(intent)

7. Types of Intents

Explicit Intent

Intent(this, DetailsActivity::class.java)

Implicit Intent

Intent(Intent.ACTION_VIEW)

8. What is AndroidManifest.xml?

Answer:

It contains:

• Activities
• Services
• Permissions
• Broadcast Receivers
• Application metadata

Example:

<uses-permission android:name="android.permission.INTERNET"/>

9. What is Context?

Answer:

Context provides access to:

• Resources
• System services
• Application environment

Example:

Toast.makeText(this, "Hello", Toast.LENGTH_SHORT).show()

10. Difference between Application Context and Activity Context

Section 2: Android Components

11. What is a Service?

Answer:

Service performs background operations.

Example:

class MusicService : Service()

Types:

• Foreground Service
• Background Service
• Bound Service

12. What is Broadcast Receiver?

Answer:

Receives system-wide events.

Example:

class BatteryReceiver : BroadcastReceiver() {
   override fun onReceive(context: Context, intent: Intent) {
   }
}

13. What is Content Provider?

Answer:

Used to share data between applications.

Example:

contentResolver.query(...)

14. What is Fragment?

Answer:

Reusable UI component hosted inside an Activity.

Example:

class HomeFragment : Fragment()

15. Fragment Lifecycle

onAttach()
onCreate()
onCreateView()
onViewCreated()
onStart()
onResume()
onPause()
onStop()
onDestroyView()
onDestroy()

Section 3: Kotlin Interview Questions

16. Why Kotlin over Java?

Answer:

Advantages:

• Null safety
• Coroutines
• Less boilerplate
• Extension functions
• Data classes

17. What is a Data Class?

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

Automatically generates:

• equals()
• hashCode()
• copy()
• toString()

18. What is Null Safety?

var name: String? = null

Safe call:

name?.length

Elvis operator:

val length = name?.length ?: 0

19. What are Extension Functions?

fun String.greet() {
   println("Hello $this")
}

Usage:

"Android".greet()

20. What are Higher Order Functions?

fun execute(action: () -> Unit) {
   action()
}

Usage:

execute {
   println("Running")
}

Section 4: Jetpack Compose

21. What is Jetpack Compose?

Answer:

Modern declarative UI toolkit for Android.

Example:

@Composable
fun Greeting() {
   Text("Hello Android")
}

22. Difference between XML and Compose

23. What is @Composable?

Answer:

Marks a function that describes UI.

@Composable
fun HomeScreen()

24. What is State in Compose?

var count by remember {
   mutableStateOf(0)
}

State changes trigger recomposition.

25. What is Recomposition?

Answer:

Compose redraws affected UI when state changes.

Section 5: MVVM Architecture

26. What is MVVM?

Layers:

View
↓
ViewModel
↓
Repository
↓
Data Source

Benefits:

• Separation of concerns
• Testability
• Maintainability

27. What is ViewModel?

class HomeViewModel : ViewModel()

Stores UI state.

Survives configuration changes.

28. What is LiveData?

val users = MutableLiveData<List<User>>()

Lifecycle-aware observable.

29. LiveData vs StateFlow

30. What is Repository Pattern?

Single source of truth for data.

class UserRepository

Handles:

• API
• Database
• Cache

Section 6: Coroutines

31. What is Coroutine?

Lightweight thread.

viewModelScope.launch {
   fetchUsers()
}

32. launch vs async

launch

launch { }

Returns Job.

async

async { }

Returns Deferred.

33. What is Dispatcher?

Dispatchers.Main
Dispatchers.IO
Dispatchers.Default

34. What is suspend function?

suspend fun getUsers()

Can pause and resume execution.

35. What is Structured Concurrency?

Child coroutines are tied to parent lifecycle.

Section 7: Flow

36. What is Flow?

flow {
   emit(1)
}

Asynchronous data stream.

37. StateFlow vs SharedFlow

38. Flow Operators

map()
filter()
debounce()
combine()
zip()

Section 8: Dependency Injection

39. What is Dependency Injection?

Providing dependencies from outside.

Benefits:

• Testability
• Scalability
• Decoupling

40. Hilt vs Dagger

41. Hilt Setup

@HiltAndroidApp
class MyApp : Application()

42. Constructor Injection

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

Section 9: Networking

43. What is Retrofit?

Popular HTTP client.

@GET("users")
suspend fun getUsers()

44. Retrofit vs Volley

45. What is OkHttp?

Network layer used by Retrofit.

46. What is Interceptor?

class AuthInterceptor : Interceptor

Used for:

• Logging
• Authentication
• Headers

47. Difference between PUT and PATCH

48. How do you handle API errors?

try {
} catch (e: Exception) {
}

Use:

• Error models
• Result wrappers
• Sealed classes

Section 10: Room Database

49. What is Room?

Jetpack ORM for SQLite.

50. Room Components

@Entity
@Dao
@Database

Example:

@Entity
data class User(
   @PrimaryKey val id:Int
)

Section 11: Android Testing

51. Unit Testing

@Test
fun loginSuccess()

52. Mockito

whenever(repo.getUsers())

53. MockK

Popular Kotlin mocking framework.

54. Espresso

UI Testing framework.

onView(withId(R.id.button))

To be continue on next part