Interview Q/A 2025 ~ Code 4 Kotlin

Android Engineer interview requires a solid understanding of Android technologies, frameworks, and practices.

Preparing for a Senior Android Engineer interview requires a solid understanding of Android technologies, frameworks, and practices. Here are 10 potential questions and answers for each topic you mentioned:

1. Kotlin

Q: What are extension functions in Kotlin, and how are they used?
A: Extension functions allow adding new functionality to existing classes without modifying their code. They’re defined with a receiver type and used like a regular member function.
Example:
```
 fun String.removeWhitespace() = this.replace(" ", "")
```
Q: What is the difference between var and val?
A: val is read-only and immutable once initialized, while var is mutable and can be reassigned.
Q: Explain Kotlin's null safety features.
A: Kotlin uses nullable types (e.g., String?) and operators (?., !!, ?:) to minimize null pointer exceptions.
Q: What are higher-order functions in Kotlin?
A: Functions that take other functions as parameters or return them.
Q: Describe Kotlin's sealed classes.
A: Sealed classes represent restricted hierarchies and allow exhaustive when-checks.
Q: How does data class differ from a regular class?
A: Data classes provide default implementations for equals(), hashCode(), and toString().
Q: What is the purpose of companion object?
A: It acts as a static equivalent for class members.
Q: How do you use inline functions, and why?
A: Inline functions prevent function call overhead by replacing the function call with its body at compile time.
Q: What is a lambda expression in Kotlin?
A: It’s a short, unnamed function defined using the {} syntax.
Q: Explain by lazy in Kotlin.
A: It initializes a property only when it’s accessed for the first time.

2. Coroutines

Q: What are coroutines in Kotlin?
A: Coroutines are a lightweight, concurrency framework for managing asynchronous tasks.
Q: What’s the difference between launch and async?
A: launch returns a Job, while async returns a Deferred which can provide results via await().
Q: How does suspend function work?
A: It’s a function that can suspend execution without blocking the thread.
Q: Explain the difference between runBlocking and CoroutineScope.
A: runBlocking blocks the thread, while CoroutineScope does not.
Q: What is a CoroutineScope?
A: A scope defines the lifecycle of coroutines launched within it.
Q: What is the purpose of Dispatchers in coroutines?
A: Dispatchers determine the thread pool used (e.g., Main, IO, Default).
Q: Explain structured concurrency.
A: It ensures that coroutines are launched in a structured way, tied to a scope, and complete predictably.
Q: How does withContext differ from launch?
A: withContext switches context and waits for the result; launch launches a new coroutine.
Q: What are Flow and its advantages over RxJava?
A: Flow is a Kotlin-native solution for handling streams of data asynchronously. It integrates better with coroutines and has less overhead.
Q: How do you handle exceptions in coroutines?
A: Using try-catch blocks or CoroutineExceptionHandler.

3. Compose

Q: What is Jetpack Compose?
A: It’s Android’s modern UI toolkit for building native UI declaratively.
Q: Explain the @Composable annotation.
A: Marks a function as composable, meaning it can define UI in a declarative manner.
Q: How does state management work in Compose?
A: Using remember, mutableStateOf, and State classes.
Q: What is remember in Compose?
A: It retains state across recompositions.
Q: How do you create a list in Compose?
A: Using LazyColumn or LazyRow.
Q: What is the difference between Modifier and LayoutModifier?
A: Modifier allows UI transformations; LayoutModifier deals specifically with layout constraints.
Q: How do you handle themes in Compose?
A: Using MaterialTheme and custom Theme composables.
Q: Explain SideEffect in Compose.
A: Executes code whenever there’s a recomposition.
Q: What is recomposition?
A: The process of redrawing the UI when state changes.
Q: How does navigation work in Compose?
A: Using NavHost and NavController.

4. MVVM

Q: What is MVVM?
A: Model-View-ViewModel, a design pattern to separate UI from business logic.
Q: Why is MVVM preferred in Android?
A: It provides a clear separation of concerns and makes UI testing easier.
Q: How does LiveData fit into MVVM?
A: It observes and reacts to changes in data, driving UI updates.
Q: What is the role of ViewModel?
A: It handles business logic and prepares data for the UI.
Q: What are common pitfalls in MVVM?
A: Overloading ViewModel with UI logic, improper lifecycle management.
Q: How do you test ViewModel?
A: Using unit tests with mocking frameworks like Mockito.
Q: Explain the role of Repository in MVVM.
A: It abstracts data sources and manages operations like caching and remote API calls.
Q: How does Hilt assist in MVVM?
A: By providing dependency injection for ViewModel and other components.
Q: How does Coroutines improve MVVM?
A: It enables asynchronous calls within ViewModel using viewModelScope.
Q: What’s the difference between MVVM and MVC?
A: In MVVM, the ViewModel communicates directly with the View, unlike the Controller in MVC.

5. Retrofit

Q: What is Retrofit, and why is it used?
A: Retrofit is a type-safe HTTP client for Android and Java, used for API calls and parsing responses.

Q: How do you define a Retrofit API interface?
A: Using annotations like @GET, @POST, and methods returning Call, Deferred, or Flow.
Example:

@GET("users/{id}")
suspend fun getUser(@Path("id") userId: Int): User

Q: What is the purpose of @Query annotation?
A: It appends query parameters to the URL.
Example: @GET("search") suspend fun searchUsers(@Query("name") name: String): List<User>
Q: How do you handle JSON responses with Retrofit?
A: By using converters like GsonConverterFactory or MoshiConverterFactory.
Q: How can you cancel a Retrofit request?
A: Use Call.cancel() or ensure proper coroutine scope cancellation when using suspend.
Q: What are interceptors in Retrofit?
A: Interceptors (via OkHttp) are used for logging, adding headers, or handling authentication.
Q: How do you handle API errors in Retrofit?
A: By checking the response code and parsing the error body if needed.
Q: What is enqueue in Retrofit?
A: It performs an asynchronous call and handles success or failure in a callback.
Q: How do you add dynamic headers to a Retrofit request?
A: Use @Header annotation or an interceptor.
Q: What’s the difference between Call and suspend in Retrofit?
A: Call is used for synchronous or asynchronous calls, while suspend integrates better with coroutines for cleaner, asynchronous API usage.

6. Dependency Injection (Hilt)

Q: What is Hilt, and why is it used?
A: Hilt is a dependency injection library for Android, simplifying Dagger integration.
Q: What is the role of @HiltAndroidApp?
A: It sets up Hilt for the entire app and generates a base class for dependency injection.
Q: What is a Module in Hilt?
A: A class annotated with @Module that provides dependencies using @Provides or @Binds.
Q: How do you inject dependencies in a ViewModel using Hilt?
A: By annotating the ViewModel with @HiltViewModel and using constructor injection.
Q: Explain the use of @Singleton in Hilt.
A: It ensures a single instance of a dependency is used throughout the app lifecycle.
Q: What is @EntryPoint in Hilt?
A: It allows dependency injection in classes not directly supported by Hilt (e.g., BroadcastReceiver).
Q: How does Hilt handle activity and fragment-scoped dependencies?
A: Using annotations like @ActivityScoped and @FragmentScoped.
Q: What’s the difference between @Provides and @Binds?
A: @Provides creates an instance, while @Binds maps an interface to an implementation.
Q: How do you test classes using Hilt?
A: Use the HiltAndroidRule and @BindValue for dependency overrides in tests.
Q: What are the benefits of using Hilt over manual DI or Service Locator patterns?
A: Simplifies setup, improves testability, ensures lifecycle-awareness, and reduces boilerplate.

7. Jetpack Architecture Components

Q: What are Jetpack Architecture Components?
A: A collection of libraries to implement modern Android app architecture, like LiveData, ViewModel, Room, etc.
Q: How does LiveData work?
A: It observes data changes and updates the UI reactively.
Q: What is the role of the ViewModel in Jetpack?
A: To manage UI-related data in a lifecycle-aware manner.
Q: What is Room, and how is it used?
A: Room is a SQLite abstraction library that provides type-safe database interactions.
Q: How do you observe LiveData in an Activity or Fragment?
A: Using the observe method.
Example: viewModel.data.observe(this) { data -> /* Update UI */ }
Q: What is DataStore, and how is it different from SharedPreferences?
A: DataStore is a modern and more robust solution for key-value storage, using Coroutines.
Q: How does Paging help in Jetpack?
A: It loads data gradually, reducing resource usage.
Q: What is WorkManager?
A: A library to schedule and manage deferrable, guaranteed background work.
Q: How do you implement lifecycle-aware components?
A: By using LifecycleObserver or LifecycleOwner.
Q: What’s the purpose of SavedStateHandle in Jetpack?
A: To save and restore UI state across configuration changes.

8. GSON

Q: What is GSON?
A: A library to convert Java/Kotlin objects to JSON and vice versa.
Q: How do you deserialize JSON using GSON?
A: Using Gson().fromJson(jsonString, MyClass::class.java).
Q: What is the difference between @SerializedName and a regular field?
A: @SerializedName maps JSON keys to class properties.
Q: Can GSON handle nested JSON?
A: Yes, by mapping nested objects to corresponding classes.
Q: How do you handle unknown fields in JSON with GSON?
A: Use JsonElement or custom deserializers.
Q: What is a TypeToken in GSON?
A: It helps deserialize generic types like List<T>.
Q: How do you serialize Kotlin data classes with default values?
A: Use the default GSON configuration, or customize the serialization policy.
Q: How do you configure GSON to exclude null values?
A: Use GsonBuilder().serializeNulls() to include or exclude nulls.
Q: What is a custom serializer in GSON?
A: A class that implements JsonSerializer or JsonDeserializer to define custom logic.
Q: How does GSON handle arrays and lists?
A: Automatically maps JSON arrays to Kotlin/Java lists.

9. Test-Driven Development (TDD)

Q: What is TDD?
A: A development methodology where tests are written before writing the actual code.
Q: What are the main benefits of TDD?
A: Improved code quality, fewer bugs, and easier refactoring.
Q: How does TDD differ from traditional testing?
A: Tests guide code implementation instead of verifying existing code.
Q: What is a red-green-refactor cycle in TDD?
A: Write a failing test (red), make it pass (green), and refactor for optimization.
Q: How do you write a unit test for ViewModel?
A: Mock dependencies and verify the outputs using assertions.
Q: What is the role of mocking in TDD?
A: It isolates the unit being tested by simulating dependencies.
Q: How do you ensure code coverage in TDD?
A: By writing comprehensive tests for all possible scenarios.
Q: What tools can you use for TDD in Android?
A: JUnit, Mockito, Espresso, Robolectric.
Q: How does TDD integrate with Agile?
A: It fits naturally into Agile’s iterative and incremental development approach.
Q: What are common pitfalls of TDD?
A: Over-testing, slow development pace, and poorly written tests.

10. CI/CD (Continuous Integration and Continuous Deployment)

Q: What is CI/CD, and why is it important?
A: CI/CD automates the integration, testing, and deployment processes, ensuring faster delivery and better quality.
Q: What tools are commonly used for CI/CD in Android development?
A: Jenkins, GitHub Actions, Bitrise, CircleCI, Travis CI.
Q: How do you set up a CI/CD pipeline for an Android project?
A: Use a CI/CD tool to automate build, run tests, and deploy APK to a distribution service (e.g., Firebase App Distribution).
Q: What is the purpose of build.gradle files in CI/CD?
A: They define how the project is built, including dependencies, plugins, and configurations.
Q: How do you implement versioning in a CI/CD pipeline?
A: Use scripts to increment versionCode and versionName dynamically during the build process.
Q: How do you run UI tests in CI/CD pipelines?
A: Use frameworks like Espresso or UIAutomator, triggered by the CI/CD tool.
Q: What is a release pipeline, and how does it differ from a build pipeline?
A: A release pipeline automates deployment to production, while a build pipeline focuses on compiling and testing.
Q: How do you ensure security in CI/CD pipelines?
A: Use secure credentials management, encrypt API keys, and limit access to pipelines.
Q: What is trunk-based development, and how does it relate to CI/CD?
A: It involves frequent merging of small changes into a shared mainline, ensuring a smooth CI/CD process.
Q: How do you integrate Firebase Crashlytics into a CI/CD pipeline?
A: Use Firebase CLI to upload dSYM or mapping files during the build process.

11. Design Patterns

Q: What are design patterns, and why are they important in Android development?
A: They are reusable solutions to common problems, ensuring cleaner, maintainable, and scalable code.
Q: Explain the MVVM pattern.
A: It separates the UI (View), business logic (ViewModel), and data source (Model) for better code management.
Q: What is the Singleton pattern, and where is it used in Android?
A: It ensures only one instance of a class exists; used in dependency injection or managing resources.
Q: How does the Observer pattern work in Android?
A: Used by LiveData, it notifies observers when data changes.
Q: What is the Factory pattern?
A: A pattern that creates objects without exposing the instantiation logic.
Q: How does the Builder pattern work in Android?
A: Simplifies object creation by providing a step-by-step construction process, e.g., AlertDialog.Builder.
Q: What is the Repository pattern in MVVM?
A: It abstracts data sources (network, database) from the ViewModel.
Q: How does the Adapter pattern apply in Android?
A: It bridges the gap between data and UI components, e.g., RecyclerView.Adapter.
Q: Explain the Strategy pattern.
A: It defines a family of algorithms, encapsulates each one, and makes them interchangeable.
Q: What is the Decorator pattern, and where is it used?
A: It adds new functionality to objects dynamically; e.g., chaining operations with OkHttp interceptors.

12. Flow

Q: What is Flow in Kotlin?
A: A cold asynchronous stream that emits values sequentially.
Q: How does Flow differ from LiveData?
A: Flow is coroutine-based and supports more operators, while LiveData is lifecycle-aware.
Q: What are the types of Flows in Kotlin?
A: Flow, StateFlow, and SharedFlow.
Q: What is the purpose of collect() in Flow?
A: It consumes emitted values from a Flow.
Q: How do you handle exceptions in a Flow?
A: Use operators like catch or onCompletion.
Q: What is StateFlow?
A: A state-holder observable that always holds the latest value and emits updates.
Q: How do you debounce API calls using Flow?
A: Use the debounce() operator to delay emissions.
Q: How do you transform data in a Flow?
A: Use operators like map, flatMapConcat, or filter.
Q: What is combine() in Flow?
A: It merges multiple flows into one by combining their emissions.
Q: How do you convert Flow into LiveData?
A: Use the asLiveData() extension function.

13. Agile Methodology

Q: What is Agile methodology?
A: An iterative and incremental approach to software development focusing on flexibility and collaboration.
Q: What are the core principles of Agile?
A: Customer satisfaction, welcoming changes, frequent delivery, and teamwork.
Q: What is the role of a sprint in Agile?
A: A time-boxed iteration where the team delivers a potentially shippable product increment.
Q: What is a Scrum Master?
A: A facilitator who ensures the Agile process runs smoothly and removes impediments.
Q: What are the differences between Scrum and Kanban?
A: Scrum is sprint-based, while Kanban focuses on continuous flow without time constraints.
Q: What is a Product Backlog?
A: A prioritized list of tasks or features for the team to work on.
Q: What is the purpose of a daily stand-up?
A: To synchronize team activities, discuss progress, and identify roadblocks.
Q: How do you handle changes to requirements during a sprint?
A: Changes are minimized in a sprint, but they can be added to the backlog for future sprints.
Q: What is a retrospective meeting?
A: A meeting to reflect on what went well, what didn’t, and how to improve.
Q: How do you measure success in Agile?
A: By delivering working software frequently, team collaboration, and customer satisfaction.

14. Kotlin Coroutines

Q: What is a coroutine in Kotlin?
A: A lightweight thread that provides concurrency without blocking the main thread.
Q: How do you start a coroutine in Kotlin?
A: Using launch, async, or runBlocking builders within a CoroutineScope.
Q: What is the difference between launch and async?
A: launch returns a Job and does not return a result, while async returns a Deferred and is used for obtaining a result.
Q: What are suspend functions?
A: Functions that can be paused and resumed, making them ideal for asynchronous programming.
Q: What is CoroutineScope?
A: A lifecycle-bound scope that manages the coroutines within it.
Q: How do you handle exceptions in coroutines?
A: Using try-catch blocks or CoroutineExceptionHandler.
Q: What is the difference between withContext and launch?
A: withContext switches the context and waits for execution to complete, whereas launch starts a new coroutine.
Q: What is Dispatchers in coroutines?
A: Dispatchers like Main, IO, and Default determine the thread on which a coroutine runs.
Q: Explain structured concurrency in Kotlin Coroutines.
A: Ensures all coroutines are completed or canceled when their parent scope ends.
Q: How do you use flowOn in coroutines?
A: To change the dispatcher for a Flow without affecting downstream operations.

15. Android Jetpack Compose

Q: What is Jetpack Compose?
A: A modern, declarative UI toolkit for building Android user interfaces.
Q: How does Compose differ from the traditional View system?
A: Compose uses a reactive programming model and eliminates the need for XML layouts.
Q: What is a Composable function?
A: A function annotated with @Composable that defines UI components.
Q: How do you manage state in Jetpack Compose?
A: Using remember and mutableStateOf for local state, or State and ViewModel for shared state.
Q: What is LaunchedEffect in Jetpack Compose?
A: A composable function that runs a block of code once when the key changes.
Q: How do you handle navigation in Jetpack Compose?
A: Using the NavHost and NavController from the Navigation Compose library.
Q: What is the role of Modifier in Compose?
A: To modify UI elements' layout, behavior, and appearance.
Q: How does recomposition work in Jetpack Compose?
A: It updates only the parts of the UI tree where state has changed.
Q: What is SideEffect in Compose?
A: A composable function that performs non-composable side effects when recomposition occurs.
Q: How do you test Jetpack Compose UIs?
A: Using ComposeTestRule and Semantics to write UI tests.

16. Test-Driven Development (TDD)

Q: What is Test-Driven Development?
A: A methodology where tests are written before writing the actual code.
Q: What are the benefits of TDD?
A: Improved code quality, fewer bugs, and better design.
Q: How do you write a unit test for a ViewModel in TDD?
A: Mock dependencies using Mockito and write tests using JUnit to validate the ViewModel’s behavior.
Q: What are mocks and stubs?
A: Mocks simulate objects for testing interactions, while stubs return predefined data for testing methods.
Q: How do you write a failing test in TDD?
A: Write a test case for functionality that hasn't been implemented yet.
Q: What is the red-green-refactor cycle in TDD?
A: Red: Write a failing test. Green: Write code to pass the test. Refactor: Optimize the code.
Q: How do you mock network responses in TDD?
A: Use libraries like MockWebServer or create custom fake repositories.
Q: How is TDD applied to UI testing?
A: Write UI tests using Espresso or Compose Test before implementing the UI components.
Q: How do you ensure code coverage in TDD?
A: By writing tests for all use cases and validating using tools like JaCoCo.
Q: What challenges are common in TDD, and how do you overcome them?
A: Writing tests for complex scenarios; use dependency injection and mocks.

17. Android Jetpack Architecture Components

Q: What are Android Jetpack components?
A: A set of libraries for building Android applications faster and easier.
Q: What is the purpose of the Lifecycle component?
A: It helps manage UI components' lifecycle-aware behavior, like LiveData.
Q: Explain LiveData and its use cases.
A: A lifecycle-aware observable that updates the UI when data changes.
Q: What is a ViewModel in Android?
A: A component that stores UI-related data to survive configuration changes.
Q: How does the Navigation component help in Android development?
A: It simplifies navigation and deep linking, reducing boilerplate code.
Q: What is DataStore in Jetpack?
A: A library for storing key-value pairs or typed objects using Kotlin Coroutines.
Q: What is Paging in Jetpack?
A: A library for loading and displaying data incrementally in RecyclerView.
Q: How does WorkManager differ from JobScheduler?
A: WorkManager is more flexible, supporting both immediate and deferred background tasks.
Q: What is the Room database?
A: A persistence library that provides an abstraction over SQLite for easier database access.
Q: How does Hilt simplify dependency injection?
A: It generates and provides bindings for Android classes, reducing boilerplate.

18. REST API and Networking

Q: What is a REST API?
A: REST (Representational State Transfer) API is a web service that uses HTTP methods (GET, POST, PUT, DELETE) to perform CRUD operations on resources.
Q: How do you integrate a REST API in an Android app?
A: By using libraries like Retrofit or Volley for HTTP requests and GSON or Moshi for parsing JSON responses.
Q: What is the purpose of an API response code?
A: It indicates the status of an HTTP request (e.g., 200 OK, 404 Not Found, 500 Internal Server Error).
Q: How do you handle API errors in an Android app?
A: By implementing error-handling mechanisms using try-catch, Retrofit interceptors, and parsing error response bodies.
Q: What is the difference between synchronous and asynchronous API calls?
A: Synchronous calls block the thread until completion, while asynchronous calls allow the thread to continue execution.
Q: How do you optimize network calls in Android?
A: By caching responses, using pagination, minimizing payload sizes, and leveraging efficient libraries like Retrofit with OkHttp.
Q: What is an interceptor in Retrofit?
A: It is a mechanism to intercept and modify requests or responses before they reach the server or client.
Q: How do you handle token-based authentication in API calls?
A: By including the token in the Authorization header of HTTP requests and refreshing expired tokens.
Q: What is the role of @SerializedName in GSON?
A: It maps JSON keys to Kotlin/Java object fields during serialization/deserialization.
Q: How do you test API calls in Android?
A: By using tools like Postman for manual testing and libraries like MockWebServer for unit tests.

19. GSON and JSON Parsing

Q: What is GSON, and how is it used in Android?
A: GSON is a Java library for converting JSON to Java/Kotlin objects and vice versa.
Q: How do you parse a JSON response using GSON?
A: By creating a data class matching the JSON structure and using Gson().fromJson() to parse.
Q: How do you handle nested JSON objects with GSON?
A: By creating corresponding nested data classes.
Q: How do you convert a Kotlin object to a JSON string?
A: By using Gson().toJson().
Q: What is the purpose of the @Expose annotation in GSON?
A: To include/exclude fields during serialization/deserialization.
Q: How do you deserialize a JSON array in GSON?
A: By using TypeToken to specify the type of the list.
Q: What is the difference between JsonElement and JsonObject in GSON?
A: JsonElement represents any JSON type, while JsonObject represents a JSON object specifically.
Q: How do you handle unknown or dynamic JSON fields in GSON?
A: By using JsonObject or a Map<String, Any>.
Q: Can GSON handle custom deserialization?
A: Yes, by implementing a custom JsonDeserializer.
Q: How do you handle optional or nullable fields in GSON?
A: By using Kotlin's nullable types or default values.

20. Android Security

Q: What are the best practices for securing sensitive data in an Android app?
A: Use EncryptedSharedPreferences, the Android Keystore system, and avoid hardcoding sensitive data.
Q: How do you secure API keys in Android?
A: By storing them in the local.properties file or using secure backend services.
Q: What is ProGuard, and how does it enhance app security?
A: ProGuard is a tool that obfuscates code, making it harder to reverse-engineer.
Q: How do you secure network communication in an Android app?
A: By using HTTPS, certificate pinning, and secure libraries like Retrofit or OkHttp.
Q: What is the role of permissions in Android security?
A: Permissions regulate access to sensitive data and system features.
Q: How do you implement biometric authentication in Android?
A: Using the BiometricPrompt API.
Q: What is an intent-filter vulnerability, and how can it be prevented?
A: It occurs when unprotected components are exposed; prevent it by declaring android:exported=false.
Q: How do you prevent SQL injection in SQLite?
A: By using parameterized queries or ORM libraries like Room.
Q: What is the Android Keystore system?
A: A secure container for cryptographic keys that cannot be extracted.
Q: How do you implement encryption in Android?
A: By using libraries like Cipher for symmetric encryption or KeyPairGenerator for asymmetric encryption.

21. Performance Optimization

Q: How do you improve UI performance in Android?
A: By optimizing layouts, reducing overdraw, and avoiding blocking the main thread.
Q: What tools do you use to monitor app performance?
A: Android Studio Profiler, Firebase Performance Monitoring, and Systrace.
Q: How do you reduce app launch time?
A: By optimizing the splash screen, preloading resources, and deferring initialization of heavy components.
Q: What is overdraw, and how do you fix it?
A: Overdraw occurs when a UI element is drawn multiple times; fix it by simplifying layouts and using LAYER_TYPE_NONE.
Q: How do you optimize RecyclerView performance?
A: By using DiffUtil, ViewHolder, and enabling setHasFixedSize.
Q: How do you detect memory leaks in an Android app?
A: By using tools like LeakCanary or Android Profiler.
Q: What are the best practices for handling large bitmaps in Android?
A: By using BitmapFactory.Options for scaling and loading in smaller resolutions.
Q: How do you improve battery efficiency in Android apps?
A: By minimizing background work, using WorkManager, and batching network requests.
Q: How do you reduce APK size?
A: By enabling code shrinking with R8, removing unused resources, and using vector drawables.
Q: How do you optimize database operations in Android?
A: By using indexing, caching queries, and keeping the database schema simple.

22. Multi-Module Architecture

Q: What is multi-module architecture in Android?
A: It's a project structure that divides an app into multiple modules, promoting reusability, faster build times, and modularized code.
Q: What types of modules can you create in an Android project?
A: App Module, Feature Module, Library Module, and Dynamic Feature Module.
Q: What are the benefits of modularizing an Android app?
A: Improved scalability, reduced build times, parallel development, and easier testing.
Q: How do you manage dependencies across multiple modules?
A: By using a centralized buildSrc or Gradle's version catalog for dependency management.
Q: How do you enable communication between modules?
A: Through interfaces, dependency injection (like Hilt), or Navigation Component for navigation.
Q: What is a dynamic feature module?
A: A module that allows specific features to be downloaded on demand using Play Feature Delivery.
Q: What is the role of the base module in a multi-module project?
A: It contains shared resources like networking, database, and core utilities.
Q: How do you structure packages in a feature module?
A: By following clean architecture layers like data, domain, and presentation.
Q: What challenges arise with multi-module architecture?
A: Managing dependencies, increased complexity, and potential code duplication without careful planning.
Q: How do you test individual modules in a multi-module app?
A: By writing unit tests for each module and integration tests to test communication between modules.

23. Android Jetpack Libraries

Q: What is Android Jetpack?
A: A collection of libraries, tools, and architectural guidance to accelerate Android app development.
Q: Name some popular Android Jetpack libraries.
A: Room, WorkManager, Navigation, LiveData, ViewModel, DataStore, Paging.
Q: How does the Navigation Component simplify navigation?
A: By providing a single source of truth for navigation and handling back stack management.
Q: What is the role of WorkManager in Android?
A: To schedule deferrable and guaranteed background tasks.
Q: How do you use Room for database management?
A: By defining entities, DAOs, and a database class annotated with @Database.
Q: What is LiveData, and how does it work?
A: LiveData is a lifecycle-aware observable data holder that updates UI components when data changes.
Q: How does the Paging library help with large datasets?
A: By loading data incrementally, reducing memory usage and improving performance.
Q: What is DataStore, and how is it different from SharedPreferences?
A: DataStore is a modern solution for data storage using Kotlin Coroutines and Flow, offering better performance and type safety.
Q: How do you implement a ViewModel in Jetpack?
A: By extending the ViewModel class and providing data to the UI using LiveData or Flow.
Q: What are the advantages of using Jetpack Compose over XML?
A: Faster UI development, declarative syntax, better state management, and integration with Kotlin.

24. Advanced Dependency Injection

Q: What is dependency injection?
A: A design pattern where dependencies are provided rather than hard-coded, improving testability and maintainability.
Q: Why use Hilt for dependency injection?
A: Hilt simplifies DI setup in Android by providing a pre-defined structure and integrating with Jetpack components.
Q: What is the difference between @Singleton and @ViewModelScoped in Hilt?
A: @Singleton creates a single instance for the entire application, while @ViewModelScoped ties the instance's lifecycle to a ViewModel.
Q: How do you inject dependencies in a Fragment using Hilt?
A: Annotate the Fragment with @AndroidEntryPoint and use @Inject for fields or constructors.
Q: What is the purpose of a @Module in Hilt?
A: To define how dependencies are provided, using @Provides or @Binds.
Q: How do you handle dependencies that require runtime arguments in Hilt?
A: By using assisted injection or passing the argument into a factory class.
Q: What is the difference between @Provides and @Binds?
A: @Provides creates an instance of a class, while @Binds maps an interface to its implementation.
Q: How do you test Hilt-injected components?
A: By using the HiltAndroidRule in tests and creating test-specific modules.
Q: How do you scope a dependency to an Activity or Fragment in Hilt?
A: By using @ActivityScoped or @FragmentScoped.
Q: What is the @EntryPoint annotation in Hilt?
A: It allows access to Hilt-generated components outside of Hilt's managed classes.

25. Test-Driven Development (TDD) in Android

Q: What is TDD?
A: A software development approach where tests are written before the actual code, ensuring the code meets requirements.
Q: What are the benefits of TDD in Android development?
A: It improves code quality, ensures reliability, and reduces debugging time.
Q: What types of tests are typically written in TDD?
A: Unit tests, integration tests, and UI tests.
Q: How do you write a failing test in TDD?
A: By creating a test case for an unimplemented feature or functionality.
Q: What is the "Red-Green-Refactor" cycle in TDD?
A: Write a failing test (Red), make it pass (Green), and refactor the code for optimization.
Q: Which tools are used for TDD in Android?
A: JUnit, Mockito, Espresso, Robolectric.
Q: How do you test a ViewModel in MVVM architecture?
A: By mocking dependencies and asserting LiveData or Flow outputs.
Q: How do you handle dependencies in TDD for Android?
A: By using dependency injection frameworks like Hilt or mocking libraries like Mockito.
Q: What are some challenges in implementing TDD?
A: Initial time investment, complex test cases, and maintaining test coverage.
Q: How do you measure TDD success in a project?
A: By tracking code coverage, reduced bugs, and consistent delivery of features.

26. Advanced Kotlin Features

Q: What are extension functions in Kotlin, and why are they useful?
A: Extension functions add functionality to existing classes without modifying their source code. They are useful for keeping the code clean and reusable.
Q: What is a sealed class in Kotlin, and how does it differ from an enum class?
A: A sealed class represents a restricted class hierarchy, where subclasses are known at compile-time. Unlike enum class, each subclass of a sealed class can hold different types of data.
Q: Explain the difference between inline, noinline, and crossinline in Kotlin.
A:
- inline: Inlines the lambda code into the call site, reducing overhead.
- noinline: Prevents the lambda from being inlined.
- crossinline: Ensures the lambda doesn’t return directly from the enclosing function.
Q: How does lazy initialization work in Kotlin?
A: lazy initializes a property only when it is first accessed. It's thread-safe by default unless specified otherwise.
Q: What are coroutines' context and dispatcher?
A:
- context: Holds metadata about the coroutine (e.g., job, dispatcher).
- dispatcher: Determines the thread on which the coroutine runs (Dispatchers.Main, Dispatchers.IO).
Q: How do you implement delegation in Kotlin?
A: By using the by keyword. For example, property delegation (val name: String by lazy { "Value" }).
Q: What is the difference between == and === in Kotlin?
A: == checks structural equality, while === checks referential equality.
Q: What are inline classes in Kotlin, and when should they be used?
A: Inline classes wrap a value and are used to avoid overhead at runtime, like type wrappers for primitives.
Q: How do you handle nullable types in Kotlin?
A: By using nullable types (?), safe calls (?.), the Elvis operator (?:), and the not-null assertion operator (!!).
Q: Explain the use of higher-order functions in Kotlin.
A: A higher-order function is a function that takes another function as a parameter or returns a function. It allows functional programming constructs like map, filter, and reduce.

27. Networking and API Handling

Q: What is Retrofit, and why is it widely used in Android?
A: Retrofit is a type-safe HTTP client for Android that simplifies API calls by converting JSON responses into Kotlin/Java objects.
Q: How do you handle network errors in Retrofit?
A: By using try-catch, onFailure callbacks, or implementing a global error-handling mechanism.
Q: What are interceptors in OkHttp, and how are they used?
A: Interceptors intercept HTTP requests and responses for logging, modifying headers, or adding authentication tokens.
Q: How do you cache API responses in Retrofit?
A: By adding a caching layer using OkHttp and setting cache policies in the client.
Q: Explain the difference between synchronous and asynchronous API calls in Retrofit.
A:
- Synchronous calls block the current thread.
- Asynchronous calls execute in the background and use callbacks to return results.
Q: How do you implement pagination with Retrofit?
A: By adding query parameters like page or offset in the API request and handling responses iteratively.
Q: What is the role of Gson in Retrofit?
A: Gson is used as a converter to serialize and deserialize JSON data.
Q: How can you use Flow with Retrofit for continuous data streams?
A: By wrapping the API response in a Flow and collecting it downstream.
Q: How do you handle SSL pinning in Retrofit?
A: By configuring OkHttp with a CertificatePinner to validate server certificates.
Q: What is the advantage of using Response wrappers in Retrofit?
A: It provides access to both the API response and metadata like HTTP status codes.

28. Jetpack Compose Advanced Topics

Q: What is recomposition in Jetpack Compose?
A: Recomposition is the process where the UI is redrawn when the state changes.
Q: How do you manage state in Jetpack Compose?
A: Using remember, rememberSaveable, or state management libraries like StateFlow and ViewModel.
Q: What is the difference between remember and rememberSaveable?
A: remember keeps state only during recomposition, while rememberSaveable persists state across configuration changes.
Q: How do you handle navigation in Jetpack Compose?
A: Using the Navigation library, NavHost, and composable routes.
Q: What are the performance best practices in Jetpack Compose?
A:
- Minimize recompositions.
- Use key for list items.
- Avoid using heavy computations in Composable functions.
Q: How do you create a custom Composable function?
A: By defining a function annotated with @Composable and using Composable building blocks like Box, Row, and Column.
Q: How does Compose handle accessibility?
A: Using semantics modifiers to describe UI elements for screen readers.
Q: What is a Modifier in Jetpack Compose?
A: A Modifier is a collection of functions that modify the appearance and behavior of a Composable.
Q: How do you debug Jetpack Compose UIs?
A: Using Debug inspector, logging state changes, and the Compose UI Tooling.
Q: What are SideEffects in Jetpack Compose?
A: They allow you to trigger non-UI operations in response to state changes (LaunchedEffect, SideEffect, DisposableEffect).

29. Kotlin Flow and Reactive Programming

Q: What is Kotlin Flow?
A: Flow is a cold stream of asynchronous data used for reactive programming.
Q: How does Flow differ from LiveData?
A: Flow is coroutine-based and supports more operations like transformations and cancellation.
Q: What are the three main operators in Flow?
A:
- emit: To send data downstream.
- collect: To receive and act on the data.
- transform: To modify emitted data.
Q: How do you handle backpressure in Flow?
A: Flow automatically handles backpressure by suspending the producer until the consumer is ready.
Q: What is the purpose of StateFlow?
A: A StateFlow emits the latest value and is hot, meaning it stays active even without a collector.
Q: How do you convert a LiveData to Flow?
A: Using the asFlow() extension function.
Q: What is the difference between StateFlow and SharedFlow?
A: StateFlow holds a single up-to-date value, while SharedFlow can emit multiple values to multiple collectors.
Q: How do you handle exceptions in Flow?
A: By using catch or onCompletion operators.
Q: What is combine in Flow?
A: It merges multiple flows into a single flow by combining their latest emitted values.
Q: How do you test Flows in unit tests?
A: By using the runBlockingTest coroutine scope and asserting emitted values.