Android Developer Interview Questions
A hiring manager's question bank for Android developers — Kotlin, the activity and fragment lifecycle, coroutines, Jetpack Compose, and architecture. Built to separate people who can follow a tutorial from people who ship stable apps to millions of devices.
Hiring an Android developer means testing for a specific kind of discipline: writing code that behaves correctly across a lifecycle you do not control. Unlike a backend service, an Android app is constantly interrupted — the screen rotates, a call comes in, the OS kills your process to reclaim memory, the user backgrounds the app for three days and comes back expecting their state intact. A candidate who does not deeply understand the activity and fragment lifecycle will write code that leaks memory, loses state on rotation, or crashes when a configuration change destroys and recreates the activity. Beyond the lifecycle, modern Android is Kotlin-first, so you want fluency in null safety, coroutines and structured concurrency for async work, and increasingly Jetpack Compose for declarative UI. The strongest signal is architectural judgement: does the candidate keep logic out of activities and fragments, use a ViewModel that survives configuration changes, reason about the main thread versus background dispatchers, and think about memory, battery, and jank on real devices rather than a fast emulator? The questions below run from Kotlin fundamentals through the lifecycle and concurrency into UI and architecture. Pair a couple of lifecycle questions with one coroutine scenario and one "your app is janky and leaking memory" discussion, and you will quickly learn whether someone has shipped and maintained a production Android app or only built a sample.
How to use these questions
Pick six to eight questions across two or three categories instead of running the whole list. Start with a Kotlin or Lifecycle question to set a baseline, then spend real time on a Coroutines & Async scenario and one Architecture or performance discussion. Follow every clean answer with "what happens on a configuration change?" or "which thread does that run on?" — the follow-up is where production experience shows.
Kotlin Fundamentals
- How does Kotlin's null safety work, and what is the difference between ?., !!, and the Elvis operator ?:
- What is the difference between val and var, and between a val and a const val?
- Explain data classes — what do they give you for free, and when would you not use one?
- What are extension functions, and when have you used one to keep code clean?
- What is the difference between a companion object and a top-level function?
- Explain higher-order functions and lambdas, and how inline changes their behaviour.
- What is the difference between a list, a mutableList, and a sequence in Kotlin?
Lifecycle & Components
- Walk me through the activity lifecycle. What happens on a screen rotation, and how do you preserve state?
- What is a ViewModel, and why does it survive a configuration change when the activity does not?
- What is the difference between an activity and a fragment, and when do you use each?
- How does the fragment lifecycle differ from the activity lifecycle, especially around the view?
- What causes a memory leak from holding a Context or a View, and how do you avoid it?
- How do you pass data between fragments safely, and why is the Bundle size limited?
- What is savedInstanceState versus a ViewModel for surviving process death?
Coroutines & Async
- What problem do coroutines solve over callbacks and AsyncTask, and what is a suspend function?
- Explain structured concurrency and what a CoroutineScope gives you.
- What is the difference between Dispatchers.Main, Dispatchers.IO, and Dispatchers.Default?
- Why should you launch coroutines in viewModelScope, and what happens to them when the ViewModel clears?
- What is the difference between launch and async/await?
- What are Flow and StateFlow, and when would you use them over LiveData?
UI, Architecture & Performance
- What changes in your mental model going from XML views to Jetpack Compose's declarative UI?
- What is recomposition in Compose, and how do you avoid unnecessary recompositions?
- Explain an MVVM architecture on Android and where the repository fits.
- A list scrolls with visible jank. How do you diagnose and fix it?
- How do you keep the main thread free, and what is an ANR?
- How would you reduce an app's battery and memory footprint?
- How do you handle dependency injection — what does Hilt or Dagger give you?
Tips for interviewing Android candidates
- Probe the lifecycle hard — rotation and process death expose more real Android skill than any syntax question.
- Reward candidates who name the exact dispatcher or thread a piece of code runs on; that habit prevents ANRs.
- Ask about a memory leak or jank they actually fixed on a real device, not an emulator.
- Check for structured-concurrency thinking; coroutines leaked outside a scope are a common production bug.
- Do not over-weight the newest Compose API; solid lifecycle and architecture fundamentals matter far more.
- Watch for candidates who put logic in activities and fragments — that signals a thin architectural mental model.
Frequently asked questions
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