More in Android & Kotlin — page 7
What is AndroidManifest.xml and what key elements does it declare?
This tests your grasp of the system-app contract. Good answers cover component registration, permissions, and build metadata like package name and target SDK. A red flag is omitting install-time system discovery.
How would you implement a type-safe Kotlin DSL for a UI Form?
Tests Kotlin DSL scoping with lambda receivers and extensions. Strong answers sketch a Form builder using initTag, explain T.() -> Unit implicit this for child elements, and add DslMarker to block scope leaks. Red flag: describing it as simple method chaining.
What is a reified type parameter in Kotlin?
Tests JVM type erasure and inline function mechanics. Strong answer: reified preserves generic types at runtime via inline expansion, enabling is T checks without Class<T> passing. Red flag: claiming reified works without inline or outside functions.
Describe coroutine cancellation mechanics and cooperative suspend functions
Tests cooperative cancellation mechanics. cancel() sets a Job to cancelling; suspend functions check this at suspension points and throw CancellationException, yet a tight non-suspending loop never checks and keeps running.
How do buffer, conflate, and collectLatest manage Kotlin Flow backpressure?
WHAT IT TESTS: Coroutine flow control and suspension-vs-dropping tradeoffs. ANSWER OUTLINE: Backpressure is fast emit vs slow collect; buffer() suspends the producer when full, conflate() drops stale values, and collectLatest() cancels active collection to…
Explain Kotlin's declaration-site variance with in and out
WHAT IT TESTS: Understanding declaration-site variance versus wildcards. ANSWER OUTLINE: out T means covariant producer (read), in T means contravariant consumer (write), removing wildcard noise. RED FLAG: Confusing in/out with bounds or claiming immutability.
What is a CoroutineDispatcher and when to use Default versus IO?
This tests thread pool selection and the CPU versus IO distinction. A strong answer maps CoroutineDispatcher to the thread pool, Default to CPU work, IO to blocking IO, and Main to the UI thread.
Hot vs cold Kotlin Flows and StateFlow use case
Tests grasp of flow lifecycle and collector behavior. A strong answer contrasts cold Flows, which restart per collector, with hot StateFlows broadcasting to all observers. Red flag: using Flow for UI state without citing config changes or initial value.
How does Structured Concurrency handle cancellations and exceptions?
This tests scope-bound lifecycle management preventing leaks. Cover scope cancellation cascading to children, exceptions propagating up to cancel siblings, and launch or async requiring a scope. A red flag is treating coroutines as fire-and-forget threads.
What is a suspend function in Kotlin and its compiler rules?
This tests your understanding of suspendable computations and compiler transformation. A strong answer notes non-blocking suspension, the call-from-suspend-context rule, and compiler support for pausing and resuming. A red flag is claiming they block threads.
Explain the difference between launch and async in Kotlin Coroutines
This tests scope behavior and side effects versus results. A strong answer says launch returns a Job for side effects, async returns a Deferred for results, and both are scope children. A red flag is using async for all tasks or ignoring exception handling.
What does inline solve for higher-order functions, and what is reified?
It tests lambda overhead and type erasure. Answer: inline flattens lambdas into call sites to remove allocation and virtual calls; reified needs inline so the compiler knows the concrete type at the call site, enabling is T checks.
Compare Kotlin apply and let scope functions
WHAT IT TESTS: Your grasp of Kotlin scope mechanics. ANSWER OUTLINE: Apply uses this and returns receiver for configuration; let uses it and returns lambda result for null-safe transforms. RED FLAG: Calling them interchangeable or ignoring return values.
When would you use a sealed class instead of an enum?
This tests closed hierarchies versus singleton constants. A strong answer contrasts enums with sealed class instances, shows a NetworkResult example with data-bearing branches, and highlights exhaustiveness.
Explain higher-order functions and implement filterAndTransform
Tests whether you can define higher-order functions and use lambdas idiomatically in Kotlin. A strong answer defines HOFs as functions that take or return functions, then implements filterAndTransform with filter and map.
Explain lateinit var versus val by lazy in Android
Tests deferred initialization and lifecycle coupling. Great answers contrast lateinit var's imperative assignment with lazy's first-access delegation, mapping lateinit to injected Activity fields and lazy to expensive computed objects.
What are the primary advantages of using a data class?
Tests Kotlin boilerplate reduction and value semantics. Name three generated functions like equals, hashCode, and copy; explain structural equality; and show copy updating immutable UI state.
What is an extension function? Write a hasWhitespace extension for String.
WHAT IT TESTS: Kotlin extensions are static dispatch, not true members. ANSWER OUTLINE: Explain receiverType.functionName adds behavior without inheritance; write hasWhitespace with any { it.isWhitespace() }. RED FLAG: Extensions modify classes or override.
Explain val vs var in Kotlin and null safety risks
WHAT IT TESTS: Kotlin mutability and compile-time null safety. ANSWER OUTLINE: val is read-only, var is mutable; nullables use ? like String?; risk is NullPointerException if checks are missed. RED FLAG: Calling val deep immutability or defaulting to !!.
Navigate between feature modules without direct dependencies?
Tests dependency inversion in modular apps. Answer by defining navigation interfaces in a shared module, implementing them in the :app module, and using DI to connect them. A red flag is suggesting direct module dependencies or using reflection for navigation.