Easy interview questions in Android & Kotlin
Explain val vs var in Kotlin and null safety risks
Val is read-only, var is mutable; nullables use ? like String?; risk is NullPointerException if checks are missed.
Explain val vs. var and null safety in Kotlin
Tests your grasp of Kotlin's core principles: immutability and compile-time null safety. Define val (read-only) vs. var (mutable), declare nullables with ?, and identify the risk as runtime NullPointerExceptions.
Explain val, var, and null safety in Kotlin
This tests your grasp of immutability and Kotlin's compile-time null safety. Define val (immutable reference) vs. var (mutable), explain nullable types using ?, and state the risk is NullPointerException. A red flag is confusing val with a constant.
What do the safe call and Elvis operators do in Kotlin?
?. yields null if receiver is null; ?: provides the right operand when left is null; chain as val len = str?.length ?: 0.
Purpose of Kotlin's safe call (`?.`) and Elvis (`?:`) operators?
This tests your grasp of Kotlin's null safety philosophy. A good answer defines the safe call (?.) for conditional access and the Elvis operator (?:) for default values, then combines them. A red flag is using verbose if/else checks for simple cases.
Purpose of safe call (`?.`) and Elvis (`?:`) operators
This tests your grasp of Kotlin's idiomatic null safety. Explain the safe call (?.) for chaining on nullables and the Elvis operator (?:) for providing defaults. Combine them in a one-line example. A multi-line if/else is a red flag.
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.
Difference between launch and async in Kotlin Coroutines
This tests your grasp of coroutine result handling and exception propagation. Explain that launch is fire-and-forget (returns Job), while async is for results (returns Deferred). Mention async defers exceptions until await().
Explain launch vs. async in Kotlin Coroutines
Tests your grasp of structured concurrency, return values, and exceptions. launch is for fire-and-forget tasks (returns Job), while async is for tasks that produce a result (returns Deferred).
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.
What is a `suspend` function in Kotlin?
Tests your grasp of Kotlin's core concurrency primitive. A suspend function can pause and resume. It must be called from another suspend function or a coroutine builder.
What is a Kotlin `suspend` function and how does it work?
Tests your grasp of Kotlin's non-blocking concurrency. A great answer defines a suspend function as pausable, states its two calling rules (from another suspend function or coroutine builder), and mentions the compiler's CPS transformation.
Explain the difference between Kotlin's let, run, with, apply, and also
Group by this (apply, run, with) vs it (let, also), then by return type.
Explain Kotlin's scope functions: let, run, with, apply, also
This tests your grasp of idiomatic Kotlin and the two key differentiators: context object (this/it) and return value (object/lambda result). A great answer defines these axes, categorizes each function, and provides a clear example.
Explain Kotlin's five scope functions: let, run, with, apply, also
This tests your grasp of idiomatic Kotlin. A great answer categorizes functions by their context object (this/it) and return value (object/lambda result). Provide a clear use case for apply (object configuration).
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.
Purpose and Key Elements of AndroidManifest.xml
Tests if you know the manifest is the app's contract with the Android OS. A good answer defines its role and lists key elements like activities, permissions, and the launcher intent. A red flag is calling it just a generic 'config file'.
Describe the purpose of the AndroidManifest.xml file
This tests if you view the manifest as a contract with the OS. Define its role, then list key elements like components (<activity>), permissions (<uses-permission>), and hardware features. A red flag is just listing tags without explaining their purpose.
What is the difference between project-level and module-level build.gradle?
Project level sets plugin repos and shared versions; module level sets dependencies, build types, and flavors.
Difference between project and module build.gradle files?
This tests your understanding of Gradle's project structure and build configuration scope. The project-level file configures global settings like repositories, while the module-level file configures specifics like dependencies and app ID.
We are hiring for this. Every open role lists the topics its interview covers, so you can prepare for the real thing rather than guessing.
See open roles