Android Certified Application Developer (AND-X01) — Questions and Answers

Question 1: What is the purpose of Android App Bundles (.aab) compared to traditional APKs?

They combine multiple apps into a single download
They let Google Play deliver only the resources and code needed for a specific device (Correct answer)
They allow apps to run without installation
They enable apps to be distributed outside the Play Store

Correct answer: They let Google Play deliver only the resources and code needed for a specific device

App Bundles enable Dynamic Delivery, where Google Play generates and serves optimized APKs containing only the resources and code needed for each specific device configuration.

Question 2: Which Android feature prevents apps from running unsigned or tampered code?

APK Signature Verification (Correct answer)
Android Verified Boot
SafetyNet
ProGuard

Correct answer: APK Signature Verification

APK Signature Verification ensures that apps are signed with a trusted key and have not been tampered with since signing.

Question 3: Which approach minimizes object allocation in performance-critical Android code to reduce garbage collection pauses?

Always use ArrayList over arrays
Increase the app's maximum heap size
Use StringBuilder instead of String concatenation in tight loops (Correct answer)
Disable hardware acceleration for frequently-redrawn views

Correct answer: Use StringBuilder instead of String concatenation in tight loops

String concatenation with + in a loop creates many intermediate String objects; StringBuilder reuses its internal buffer, reducing GC pressure in tight loops.

Question 4: What is the principle of least privilege in Android development?

Giving users the least access to app features
Using the lowest API level possible
Requesting only the permissions absolutely necessary for the app to function (Correct answer)
Running the app with minimal system resources

Correct answer: Requesting only the permissions absolutely necessary for the app to function

The principle of least privilege means declaring only the minimum required permissions to reduce the attack surface and potential harm if the app is compromised.

Question 5: Which library is commonly used for type-safe HTTP client calls in Android?

Retrofit (Correct answer)
HttpURLConnection
OkHttp
Volley

Correct answer: Retrofit

Retrofit turns HTTP API calls into Kotlin/Java interfaces with annotations, providing type-safe REST client functionality.

Question 6: What is the purpose of the RecyclerView.RecycledViewPool in Android?

To persist scroll position across configuration changes
To cache network responses for list items
To share recycled ViewHolders across multiple RecyclerViews (Correct answer)
To limit the number of views that can be inflated

Correct answer: To share recycled ViewHolders across multiple RecyclerViews

RecycledViewPool allows multiple RecyclerViews to share a pool of recycled ViewHolders, reducing view inflation overhead when displaying similar list content.

Question 7: Which lifecycle callback is invoked when an Activity is partially obscured by a dialog-themed Activity but still visible?

onDestroy()
onStop()
onSaveInstanceState() only
onPause() (Correct answer)

Correct answer: onPause()

onPause() fires when the Activity loses focus but remains partially visible, while onStop() only fires when fully hidden.

Question 8: What does not have any UI components and runs in the background?

Services (Correct answer)
Intents
Content Providers
Applications

Correct answer: Services

A Service is an application component that can perform long-running operations in the background without providing a user interface. Services can continue to run even if the user switches to another application, making them suitable for tasks like playing music, performing network operations, or syncing data in the background.

Question 9: Which mode in Android can developers enable to detect accidental disk or network access on the main thread?

Debug mode
ART mode
StrictMode (Correct answer)
ProGuard mode

Correct answer: StrictMode

StrictMode detects and reports violations such as disk reads/writes and network calls on the main thread, helping developers catch performance mistakes early.

Question 10: Which Android API checks whether a runtime permission has been granted?

ContextCompat.checkSelfPermission() (Correct answer)
Permission.isGranted()
ActivityCompat.requestPermissions()
PackageManager.hasPermission()

Correct answer: ContextCompat.checkSelfPermission()

ContextCompat.checkSelfPermission() returns PERMISSION_GRANTED or PERMISSION_DENIED to indicate whether the app has a specific runtime permission.

Question 11: When using Room database, what should you avoid doing on the main thread to prevent ANR errors?

Annotating entity classes
Running database queries synchronously (Correct answer)
Using LiveData return types
Defining DAO interfaces

Correct answer: Running database queries synchronously

Room by default throws an exception if database queries are run on the main thread; they should be executed on a background thread (e.g., using coroutines or LiveData) to prevent blocking the UI.

Question 12: What is the purpose of the ContentProvider in Android?

To share data between apps using a standard interface (Correct answer)
To manage local SQLite databases
To sync data with a server
To provide UI content

Correct answer: To share data between apps using a standard interface

ContentProvider allows an app to expose its data to other apps through a standardized URI-based interface.

Question 13: What is a Flow in Kotlin coroutines?

An asynchronous stream of values that can be collected over time (Correct answer)
A type of coroutine dispatcher
A network stream
A database cursor

Correct answer: An asynchronous stream of values that can be collected over time

Kotlin Flow is a cold asynchronous stream that sequentially emits multiple values over time, built on top of coroutines.

Question 14: Which class is used to encrypt data using the Android Keystore in modern Android?

KeyGenerator
SecretKeyFactory
Cipher (Correct answer)
EncryptionManager

Correct answer: Cipher

The Cipher class from javax.crypto is initialized with keys from the Android Keystore to perform encryption and decryption operations.

Question 15: What does the suspend keyword do to a Kotlin function?

Delays its execution
Marks it as a suspending function that can be paused and resumed (Correct answer)
Makes it run on a background thread
Pauses the function permanently

Correct answer: Marks it as a suspending function that can be paused and resumed

The suspend keyword marks a function as a coroutine that can suspend its execution without blocking the calling thread.

Question 16: How do you perform a database migration in Room when the schema changes?

By providing a Migration object with SQL migration scripts (Correct answer)
By using @SchemaVersion annotation
By deleting and recreating the database
Room handles migrations automatically

Correct answer: By providing a Migration object with SQL migration scripts

Room requires you to provide a Migration object containing the SQL statements needed to transform the old schema to the new one.

Question 17: Which testing framework is used for writing unit tests in Android projects?

JUnit (Correct answer)
Espresso
Mockito
Robolectric

Correct answer: JUnit

JUnit is the standard testing framework for writing and running unit tests in Android and Java/Kotlin projects.

Question 18: What annotation marks a class as a Room database entity?

@Table
@DatabaseObject
@Model
@Entity (Correct answer)

Correct answer: @Entity

The @Entity annotation marks a Kotlin or Java class as a Room database table, with each field mapping to a column.

Question 19: After being installed on a device, each Android program is stored in a _______ .

Binder (Correct answer)
None of the above
Messenger
AIDL

Correct answer: Binder

After installation, each Android application runs in its own process, and inter-process communication (IPC) between these processes is facilitated by the Binder mechanism. The Binder is a high-performance IPC system that allows components from different applications to communicate securely and efficiently. It enables services to be called across process boundaries.

Question 20: What is the main benefit of using ConstraintLayout over nested LinearLayouts or RelativeLayouts?

It flattens the view hierarchy, reducing measure/layout passes (Correct answer)
It removes the need for ViewHolders in RecyclerView
It supports hardware acceleration by default
It automatically caches view positions

Correct answer: It flattens the view hierarchy, reducing measure/layout passes

ConstraintLayout expresses complex layouts in a single flat hierarchy, avoiding nested layouts that require multiple measure/layout passes and hurt rendering performance.

Question 21: In Android, which of the following are the screen sizes?

Extralarge
Large
All of the above (Correct answer)
Small

Correct answer: All of the above

Android supports a variety of screen sizes to accommodate the diverse range of devices available in the market. These categories include small, normal, large, and extra-large. Developers design their layouts to be flexible and responsive, ensuring a consistent and optimal user experience across all these different screen dimensions.

Question 22: What is SQL injection and how does Room protect against it?

Room encrypts all queries
Room validates input length
Room uses parameterized queries with placeholders that prevent user input from being interpreted as SQL (Correct answer)
Room uses stored procedures

Correct answer: Room uses parameterized queries with placeholders that prevent user input from being interpreted as SQL

Room's @Query annotation uses parameterized queries where user input is bound as data, not parsed as SQL, preventing injection attacks.

Question 23: What return type should a Room DAO method use to observe database changes reactively?

Observable<T>
LiveData<T>
Flow<T>
Both A and B (Correct answer)

Correct answer: Both A and B

Room supports both Flow<T> and LiveData<T> as return types for DAO queries, enabling reactive observation of database changes.

Question 24: In Kotlin, what does a 'sealed class' provide when modeling UI states like Loading, Success, and Error?

Persistence of state across sessions
Thread-safe state mutation
Automatic JSON serialization of each state
A restricted class hierarchy enabling exhaustive when-expression handling (Correct answer)

Correct answer: A restricted class hierarchy enabling exhaustive when-expression handling

Sealed classes limit subclasses to a known set, so a when expression can be checked for exhaustiveness at compile time.

Question 25: Which view group is recommended for building flat, complex UI hierarchies in Android?

LinearLayout
ConstraintLayout (Correct answer)
TableLayout
GridLayout

Correct answer: ConstraintLayout

ConstraintLayout allows you to create complex layouts with a flat view hierarchy, improving rendering performance.

Question 26: Which WorkManager work type is guaranteed to run even after a device reboot?

Both A and B (Correct answer)
Neither — WorkManager doesn't survive reboots
PeriodicWorkRequest with persistence
OneTimeWorkRequest

Correct answer: Both A and B

WorkManager persists both OneTimeWorkRequest and PeriodicWorkRequest to a database, ensuring they survive app restarts and device reboots.

Question 27: Which SQL clause is used in a Room @Query to filter results?

WHERE (Correct answer)
CONDITION
HAVING
FILTER

Correct answer: WHERE

The WHERE clause in Room SQL queries filters rows that meet a specified condition, just as in standard SQL.

Question 28: Which file access mode should be used to append data to a file in Android?

MODE_PRIVATE
MODE_APPEND (Correct answer)
MODE_WRITE_ONLY
MODE_WORLD_READABLE

Correct answer: MODE_APPEND

MODE_APPEND opens the file in append mode so new data is added to the end rather than overwriting existing content.

Question 29: Which Room annotation defines a foreign key relationship between two entities?

@ForeignKey inside @Entity (Correct answer)
@Relation
@Join
@Reference

Correct answer: @ForeignKey inside @Entity

The @ForeignKey annotation within @Entity defines referential integrity constraints between two Room database tables.

Question 30: What is a test double in Android unit testing?

An object that substitutes a real dependency in a test (mock, stub, fake, spy) (Correct answer)
A test that runs twice
A duplicate test scenario
A secondary test file

Correct answer: An object that substitutes a real dependency in a test (mock, stub, fake, spy)

A test double is any substitute object used in place of a real dependency during testing, including mocks, stubs, fakes, and spies.

Question 31: What method inflates a layout resource in Android?

Both A and B (Correct answer)
LayoutInflater.inflate()
Context.inflate()
View.inflate()

Correct answer: Both A and B

Both LayoutInflater.inflate() and View.inflate() can be used to instantiate a layout XML file into its corresponding View objects.

Question 32: What is the role of the 'launch profiling' feature in Android Studio's CPU Profiler?

It records CPU activity from the very beginning of app startup to diagnose slow launches (Correct answer)
It profiles GPU shader compilation
It tracks background service CPU usage
It simulates low-end device CPU speeds

Correct answer: It records CPU activity from the very beginning of app startup to diagnose slow launches

Launch profiling captures CPU traces from process start, enabling developers to identify initialization bottlenecks that contribute to slow cold or warm start times.

Question 33: Which component should be used to expose an app's data to other applications in a secure, structured way?

Fragment
Service
ContentProvider (Correct answer)
BroadcastReceiver

Correct answer: ContentProvider

ContentProvider is the standard component for sharing structured data across app boundaries with permission control.

Question 34: Which DataStore type stores typed objects using Protocol Buffers?

Proto DataStore (Correct answer)
Preferences DataStore
Object DataStore
Typed DataStore

Correct answer: Proto DataStore

Proto DataStore stores data as typed Protocol Buffer objects, providing type safety and avoiding string keys used in Preferences DataStore.

Question 35: Which Android feature allows deferring the inflation of part of a layout until it is actually needed, improving initial load time?

ConstraintLayout chains
MotionLayout
ViewStub (Correct answer)
Data Binding

Correct answer: ViewStub

ViewStub is a lightweight, invisible View that is replaced by the inflated layout only when explicitly made visible or inflated, reducing startup inflation cost.

Question 36: Which Jetpack component is the recommended replacement for SharedPreferences?

Room
LiveData
DataStore (Correct answer)
WorkManager

Correct answer: DataStore

Jetpack DataStore is the recommended replacement for SharedPreferences, offering asynchronous, consistent, and transactional data storage.

Question 37: Which Android image format is preferred for app assets because it offers superior lossless and lossy compression compared to PNG and JPEG?

BMP
SVG
TIFF
WebP (Correct answer)

Correct answer: WebP

WebP provides significantly better compression than PNG (lossless) and JPEG (lossy) at comparable quality, reducing APK size and runtime memory usage.

Question 38: What does the dp unit represent in Android?

Density-independent pixels (Correct answer)
Default pixels
Device pixels
Drawable pixels

Correct answer: Density-independent pixels

dp (density-independent pixels) is a virtual unit that scales based on screen density to ensure consistent physical size across devices.

Question 39: What is the purpose of the Truth assertion library in Android testing?

To validate JSON truthfulness
To verify UI truth states
To provide fluent, readable assertion methods as an alternative to JUnit assertions (Correct answer)
To check permissions truthfully

Correct answer: To provide fluent, readable assertion methods as an alternative to JUnit assertions

Google's Truth library provides a fluent API for writing assertions that produce more readable failure messages than standard JUnit assertions.

Question 40: What is the purpose of SharedPreferences in Android?

To manage user accounts
To store large files
To store small amounts of primitive key-value data persistently (Correct answer)
To share data between apps

Correct answer: To store small amounts of primitive key-value data persistently

SharedPreferences provides a mechanism for storing and retrieving small amounts of primitive data as key-value pairs that persist across app sessions.

Question 41: What is the purpose of BiometricPrompt in Android?

To register new biometric templates
To encrypt biometric data
To authenticate users using fingerprint, face, or device credentials (Correct answer)
To show a fingerprint scanner UI

Correct answer: To authenticate users using fingerprint, face, or device credentials

BiometricPrompt provides a standardized API for authenticating users with biometrics or device credentials like PIN/password.

Question 42: What is the role of an Intent filter declared on an Activity?

It caches intents for later delivery
It advertises which implicit intents the Activity can handle (Correct answer)
It blocks other apps from launching the Activity
It converts explicit intents into implicit ones

Correct answer: It advertises which implicit intents the Activity can handle

Intent filters let the system match implicit intents, such as viewing a URL, to Activities that declare they can handle them.

Question 43: What does the FLAG_SECURE window flag do in Android?

Prevents the screen content from appearing in screenshots and screen recordings (Correct answer)
Encrypts window data
Prevents screenshots from being saved
Locks the screen

Correct answer: Prevents the screen content from appearing in screenshots and screen recordings

FLAG_SECURE marks an Activity's window as secure, preventing its content from appearing in screenshots, recent apps thumbnails, and screen recordings.

Question 44: What is the purpose of declaring permissions in AndroidManifest.xml?

To hide the app from unauthorized users
To encrypt app data
To declare what capabilities or data access the app requires (Correct answer)
To restrict other apps from running

Correct answer: To declare what capabilities or data access the app requires

Declaring permissions in the manifest tells the Android system and users what sensitive resources or data the app needs access to.

Question 45: Which of the following businesses purchased Android?

None of the above
Nokia
Google (Correct answer)
Apple

Correct answer: Google

Android Inc. was originally founded in 2003 by Andy Rubin, Rich Miner, Nick Sears, and Chris White. Google acquired Android Inc. in 2005, recognizing the potential of its mobile operating system. This acquisition was a pivotal moment that led to Android's development and eventual release as a dominant mobile platform.

Android Certified Application Developer (AND-X01)

The AndroidATC AND-X01 certification validates skills in Android application development including core Android APIs, UI design, data storage, security, performance optimization, background processing, and testing.

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