Android Interview Questions

Welcome to the android-interview-questions repository! This collection of categorized questions will help you prepare for interviews as an Android Developer.

Table of Contents

• Object-Oriented Programming
• Kotlin Language
• Android Framework & SDK
• Coroutines & Concurrency
• Architectures & Design Patterns
• Data & Storage
• Build, Dependencies & Tools
• Testing & Code Quality
• Security
• Accessibility & Miscellaneous

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Object-Oriented Programming

• What is the difference between method overloading and method overriding?
• How do abstract classes differ from interfaces?
• What happens when multiple interfaces declare the same method signature?
• If several interfaces provide default implementations, what issues can arise when implementing them together?
• How can you achieve multiple inheritance in Java/Kotlin?
• Explain polymorphism and inheritance with examples.

Kotlin Language

• What does the reified keyword do in generics?
• Compare let, run, with, also, and apply—when would you use each?
• How do you implement a singleton in Kotlin? Is your solution thread-safe?
• What is the difference between const val and val?
• Describe Kotlin’s visibility modifiers and explain lateinit vs lazy.
• What are inline and crossinline functions?
• How do you call a suspend function? What characteristics do suspend functions have?

Android Framework & SDK

• What is a Context, and what types of Context exist?
• Differentiate between Activity, Fragment, and Service.
• Can a fragment exist without a parent activity? In what scenario?
• What is an ANR, and after how many seconds does the system trigger it?
• How does Android protect an app’s data from unauthorized access by other apps?
• What is Doze Mode, and how does it affect background tasks and services?
• How does Android handle configuration changes (e.g., screen rotation), and how do you preserve UI state?
• Is it possible for an activity’s onDestroy() to run without onPause() or onStop() first? Explain.

Coroutines & Concurrency

• Define a coroutine and explain how it works.
• What is a CoroutineContext, and what contexts are commonly used?
• How do you start a coroutine? Compare error handling in launch vs. async.
• If a child coroutine fails inside a launch block, what happens to its siblings?
• How do you cancel a coroutine, and what must you do to ensure long-running tasks respect cancellation?
• Why is synchronized not recommended in coroutines? Can you use a Mutex instead?
• What is a race condition, and how can you prevent it?
• What concurrency utilities are available on Android?

Architectures & Design Patterns

• Compare MVVM and MVP. What other architectural patterns do you know?
• How would you integrate Jetpack Compose into an existing XML-based application?
• What responsibilities does the ViewModel have in MVVM?
• What is ViewModelScope, and why is it useful when working with coroutines?
• How do you implement dependency injection? Compare Koin and Hilt.
• What is Clean Architecture, and how does it structure application layers?
• How do you configure build variants vs. product flavors in Gradle?

Data & Storage

• Compare Room, DataStore, and SharedPreferences.
• What is a database migration, and how would you change a column’s type (e.g., String → Int) in a released app?
• How do you serialize data between screens? Compare Serializable and Parcelable.
• Why does Serializable work even though it has no methods?
• How would you store sensitive data locally to ensure security?
• Explain the differences between hot and cold streams. Compare Flow, StateFlow, and SharedFlow.
• What is back pressure in RxJava, and how do you handle it?

Build, Dependencies & Tools

• How can you verify a library doesn’t depend on outdated versions of other artifacts if you don’t have source access?
• Why can’t a Kotlin library module depend on an Android Library module?
• Compare R8 and ProGuard. Why are they necessary?
• What is linting, and which lint tools have you used?
• How do you configure build variants and flavors in Gradle?

Testing & Code Quality

• How do you write unit tests for ViewModels and coroutines? What should you cover?
• What makes a test reliable and maintainable?
• How do you detect and fix a memory leak? Provide an example.
• How do you ensure a Composable is stable and doesn’t cause unnecessary recompositions?
• Which tools do you use for performance monitoring and leak detection (e.g., LeakCanary)?

Security

• How do you protect an Android app from decompilation and unauthorized code access?
• How do you encrypt and securely store sensitive data on the device?
• How do ProGuard/R8 optimizations contribute to app security?

Accessibility & Miscellaneous

• How do you add accessibility content descriptions (TalkBack) for a Button in Compose?
• What constitutes a side effect in Compose, and how do you manage them?
• What benefits do data classes provide in Kotlin? Which methods are automatically generated?
• Can two apps with the same package name be installed on the same device?
• What is your favorite Kotlin feature, and why?
• How do you ensure your code can’t be improved further? What does that mean during code reviews?

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Good luck with your interview preparation!