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

Question 1: What is Java bytecode compiled into while developing an Android app?

Dalvik byte code (Correct answer)
Java class files
source code
Java source code

Correct answer: Dalvik byte code

During Android app development, Java source code is first compiled into standard Java bytecode (.class files). This Java bytecode is then further processed by the Dex Compiler (historically `dx`, now `d8`) into Dalvik bytecode (.dex files). This Dalvik bytecode is optimized for the Android Runtime (ART) or the older Dalvik virtual machine, which executes the app on the device.

Question 2: What does the Android vitals metric 'ANR rate' measure?

The rate at which background processes are killed by the OS
The average number of crashes per session
The percentage of daily active users who experienced an Application Not Responding dialog (Correct answer)
The percentage of sessions with network request failures

Correct answer: The percentage of daily active users who experienced an Application Not Responding dialog

ANR (Application Not Responding) rate in Android vitals measures the proportion of daily active users who encountered an ANR dialog, a key indicator of main-thread blocking issues.

Question 3: Which Android API is used to detect if the device is rooted or compromised?

SafetyNet Attestation API (deprecated)
Root Checker API
Play Integrity API
Both A and B (Correct answer)

Correct answer: Both A and B

Both the Play Integrity API (current) and the deprecated SafetyNet Attestation API assess device integrity and detect rooting or tampering.

Question 4: What does the FLAG_SECURE window flag do in Android?

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

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 5: What does ProGuard/R8 do in Android release builds?

Validates permissions
Encrypts APK resources
Shrinks, obfuscates, and optimizes code (Correct answer)
Signs the APK

Correct answer: Shrinks, obfuscates, and optimizes code

ProGuard/R8 removes unused code, renames classes and methods to short names, and optimizes bytecode to reduce APK size and hinder reverse engineering.

Question 6: Which method is used to get or create an instance of a Room database?

RoomDatabase.create()
Room.getInstance()
RoomDatabase.build()
Room.databaseBuilder() (Correct answer)

Correct answer: Room.databaseBuilder()

Room.databaseBuilder() creates or opens a Room database with the specified context, class, and database name.

Question 7: What does the LiveData class guarantee that a plain observable does not?

Lifecycle-aware delivery, so observers only receive updates while active (Correct answer)
Observers are notified even after onDestroy()
Updates are delivered on a background thread
Values are persisted across reboots

Correct answer: Lifecycle-aware delivery, so observers only receive updates while active

LiveData respects the observer's lifecycle, delivering data only to started or resumed components and auto-removing destroyed ones.

Question 8: Which library is used for mocking dependencies in Android unit tests?

Robolectric
Espresso
JUnit
Mockito (Correct answer)

Correct answer: Mockito

Mockito is a popular mocking framework that creates fake implementations of dependencies, allowing you to isolate the code under test.

Question 9: Which component should be used to expose an app's data to other applications in a secure, structured way?

Fragment
BroadcastReceiver
ContentProvider (Correct answer)
Service

Correct answer: ContentProvider

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

Question 10: Where are Android unit tests located in a project structure?

test/unit/java
src/androidTest/java
src/main/test
src/test/java (Correct answer)

Correct answer: src/test/java

Unit tests are placed in the src/test/java directory and run locally on the JVM without Android framework dependencies.

Question 11: Which method should you override to handle the result of a runtime permission request?

onPermissionResult
onPermissionGranted
onRequestPermissionsResult (Correct answer)
onActivityResult

Correct answer: onRequestPermissionsResult

onRequestPermissionsResult is called after the user responds to a permission request dialog, providing the granted or denied results.

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

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

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 13: What happens to data in getCacheDir() when the device runs low on storage?

The app crashes
Nothing happens
The system may delete cache files automatically (Correct answer)
The data is moved to external storage

Correct answer: The system may delete cache files automatically

Files in the cache directory may be deleted by the system when storage is low, so apps should not rely on them for critical data.

Question 14: Which layout in Android arranges child views in a single row or column?

LinearLayout (Correct answer)
RelativeLayout
FrameLayout
ConstraintLayout

Correct answer: LinearLayout

LinearLayout arranges its child views sequentially in either a horizontal or vertical direction.

Question 15: What is the primary purpose of the AndroidManifest.xml file?

Storing user preferences at runtime
Defining Gradle build dependencies
Holding string translations
Declaring app components, permissions, and metadata to the system (Correct answer)

Correct answer: Declaring app components, permissions, and metadata to the system

The manifest declares Activities, Services, permissions, and other essential app information to the Android system.

Question 16: Which Room annotation is used to define data access methods?

@Database
@Repository
@Dao (Correct answer)
@Query

Correct answer: @Dao

@Dao marks an interface or abstract class as a Data Access Object, which contains methods for interacting with the database.

Question 17: What is the principle of least privilege in Android development?

Giving users the least access to app features
Requesting only the permissions absolutely necessary for the app to function (Correct answer)
Using the lowest API level possible
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 18: How do you perform a database migration in Room when the schema changes?

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

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 19: What does APK size optimization technique 'code shrinking' do via R8 or ProGuard?

Splits the APK by screen density
Reduces the number of Activities in the manifest
Compresses image assets into WebP format
Removes unused classes, fields, methods, and attributes from the compiled output (Correct answer)

Correct answer: Removes unused classes, fields, methods, and attributes from the compiled output

Code shrinking with R8/ProGuard analyzes the code graph and removes unused classes, fields, methods, and attributes, producing a smaller, faster APK.

Question 20: Which Android API checks whether a runtime permission has been granted?

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

Correct answer: ContextCompat.checkSelfPermission()

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

Question 21: What is the main benefit of using ConstraintLayout over nested LinearLayouts or RelativeLayouts?

It removes the need for ViewHolders in RecyclerView
It flattens the view hierarchy, reducing measure/layout passes (Correct answer)
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 22: What is the difference between unit tests and instrumentation tests in Android?

Unit tests run on JVM; instrumentation tests run on an Android device or emulator (Correct answer)
Unit tests are slower than instrumentation tests
There is no difference
Instrumentation tests don't require an emulator

Correct answer: Unit tests run on JVM; instrumentation tests run on an Android device or emulator

Unit tests run locally on the JVM and are fast, while instrumentation tests run on an Android device/emulator and can access the Android framework.

Question 23: What is the recommended way to load large bitmaps efficiently to avoid OutOfMemoryError in Android?

Increase the app's heap size in the manifest
Use BitmapFactory.Options to subsample the bitmap before decoding (Correct answer)
Load the full bitmap and then scale it in an ImageView
Convert all images to PNG format

Correct answer: Use BitmapFactory.Options to subsample the bitmap before decoding

Setting BitmapFactory.Options.inSampleSize decodes a subsampled version of the bitmap, reducing memory usage significantly before the bitmap is loaded into memory.

Question 24: What does the term REST stand for in the context of Android networking?

Resource Exchange Standard Transfer
Remote Execution State Transfer
Reliable Endpoint Service Transfer
Representational State Transfer (Correct answer)

Correct answer: Representational State Transfer

REST (Representational State Transfer) is an architectural style for building scalable web services using standard HTTP methods.

Question 25: What return type should a Room DAO method use to observe database changes reactively?

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

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 26: Which Android Jetpack library provides an abstraction layer over SQLite for local data persistence?

Room (Correct answer)
LiveData
SQLiteOpenHelper
DataStore

Correct answer: Room

Room is a persistence library that provides compile-time verification of SQL queries and abstracts SQLite database access.

Question 27: What is SQL injection and how does Room protect against it?

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

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 28: What annotation marks a class as a Room database entity?

@Table
@Model
@DatabaseObject
@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 29: Which approach minimizes object allocation in performance-critical Android code to reduce garbage collection pauses?

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

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 30: What does the @Before annotation do in JUnit?

Indicates a precondition assertion
Marks a method to run before each test method in the class (Correct answer)
Marks a setup method that runs once
Runs code before the test class loads

Correct answer: Marks a method to run before each test method in the class

@Before marks a method that JUnit executes before each @Test method, commonly used for test setup like initializing objects.

Question 31: What is the purpose of the NetworkSecurityConfig in Android?

To manage VPN connections
To define trusted Certificate Authorities and network security policies (Correct answer)
To configure WiFi settings
To set firewall rules

Correct answer: To define trusted Certificate Authorities and network security policies

NetworkSecurityConfig allows you to customize network security settings like trusted CAs, cleartext traffic, and certificate pinning via XML.

Question 32: Which SQL clause is used in a Room @Query to filter results?

CONDITION
HAVING
FILTER
WHERE (Correct answer)

Correct answer: WHERE

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

Question 33: What does the term 'memory leak' mean in Android development?

The GPU runs out of texture memory
An object is kept in memory longer than its intended lifecycle (Correct answer)
The app writes too much data to disk
The app uses too much network bandwidth

Correct answer: An object is kept in memory longer than its intended lifecycle

A memory leak occurs when references prevent the garbage collector from reclaiming objects whose lifecycle has ended, such as an Activity referenced by a static field.

Question 34: When using DiffUtil with RecyclerView, what is the main performance advantage over calling notifyDataSetChanged()?

It calculates the minimal set of changes and animates only affected items (Correct answer)
It prevents the RecyclerView from scrolling during updates
It batches all updates into a single transaction
It moves list operations to a background thread automatically

Correct answer: It calculates the minimal set of changes and animates only affected items

DiffUtil computes the difference between two lists and dispatches granular add/remove/move/change events, avoiding the full rebind that notifyDataSetChanged() triggers.

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

ViewStub (Correct answer)
MotionLayout
Data Binding
ConstraintLayout chains

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 RecyclerView component is responsible for measuring and positioning item views?

RecycledViewPool
LayoutManager (Correct answer)
ItemDecoration
ViewHolder

Correct answer: LayoutManager

The LayoutManager in RecyclerView handles the layout strategy for its child views, such as linear, grid, or staggered arrangements.

Question 37: In Android, which of the following are the screen sizes?

Small
Large
All of the above (Correct answer)
Extralarge

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 38: Which HTTP method is used to update a resource partially in REST APIs?

PATCH (Correct answer)
POST
PUT
UPDATE

Correct answer: PATCH

PATCH is used to apply partial modifications to a resource, while PUT replaces the entire resource.

Question 39: What is the purpose of the RecyclerView.RecycledViewPool in Android?

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

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 40: You'll need an AVD to make an emulator. What exactly does it mean?

Android Virtual Display
Active Virtual Device
Application Virtual Display
Android Virtual Device (Correct answer)

Correct answer: Android Virtual Device

AVD stands for Android Virtual Device. It is a configuration that defines the characteristics of an Android phone, tablet, or other device that you want to simulate in the Android Emulator. An AVD specifies the Android version, hardware features, and screen size for the virtual device, allowing developers to test their apps on various configurations.

Question 41: Which library is used for efficient image loading from URLs in Android apps?

Glide
All of the above (Correct answer)
Picasso
Coil

Correct answer: All of the above

Glide, Picasso, and Coil are all popular Android image loading libraries that handle downloading, caching, and displaying images from URLs.

Question 42: Which component in Material Design is used to display brief, non-disruptive messages at the bottom of the screen?

AlertDialog
Dialog
Toast
Snackbar (Correct answer)

Correct answer: Snackbar

Snackbar provides brief feedback about an operation at the bottom of the screen and can include an optional action.

Question 43: What permission is required for an Android app to access the internet?

android.permission.ONLINE
android.permission.INTERNET (Correct answer)
android.permission.NETWORK
android.permission.ACCESS_NETWORK

Correct answer: android.permission.INTERNET

The android.permission.INTERNET permission must be declared in AndroidManifest.xml for an app to make network requests.

Question 44: What is the purpose of the EncryptedSharedPreferences in Android?

To encrypt network traffic
To store encrypted database credentials
To share encrypted files between apps
To encrypt both keys and values stored in SharedPreferences (Correct answer)

Correct answer: To encrypt both keys and values stored in SharedPreferences

EncryptedSharedPreferences from Jetpack Security encrypts both the keys and values using AES-256, protecting sensitive preference data at rest.

Question 45: What does WAL mode stand for in SQLite?

Web API Layer
Write and Load
Write Access Lock
Write-Ahead Logging (Correct answer)

Correct answer: Write-Ahead Logging

WAL (Write-Ahead Logging) mode in SQLite allows concurrent reads and writes, improving performance in multi-threaded apps.

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.

Questions

90 min

Time Limit

70%

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