1. Which type is used to expose a continuously updated value from a ViewModel to the UI?
- Intent
- Bundle
- StateFlow (or LiveData)
- Cursor
Answer: C) StateFlow (or LiveData)
Explanation: StateFlow holds the latest state and emits updates.
MCQs / Computer Science / Threading and Publishing Android Applications
Threading and Publishing Android Applications MCQs — Computer Science
34 multiple-choice questions on Threading and Publishing Android Applications from Computer Science, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.
2. AsyncTask was deprecated in:
- Android 14
- Android 8.0
- Android 11 (API 30)
- Android 5.0
Answer: C) Android 11 (API 30)
Explanation: AsyncTask is deprecated from API 30; use coroutines or executors.
3. Updating a TextView from a background thread causes:
- OutOfMemoryError
- NetworkOnMainThreadException
- CalledFromWrongThreadException
- ActivityNotFoundException
Answer: C) CalledFromWrongThreadException
Explanation: Only the UI thread may touch views.
4. "Structured concurrency" means:
- Threads are created manually
- All coroutines run in a fixed order
- Coroutines can only run once
- Coroutines are children of a scope, so cancelling the scope cancels them all
Answer: D) Coroutines are children of a scope, so cancelling the scope cancels them all
Explanation: It prevents leaked coroutines.
5. Which class is deprecated and replaced by WorkManager or JobIntentService alternatives?
- IntentService
- Activity
- Service
- Fragment
Answer: A) IntentService
Explanation: IntentService is deprecated from API 30.
6. Which method runs code on the UI thread from a background thread inside an activity?
- runInBackground
- Thread.sleep()
- runOnUiThread
- startService()
Answer: C) runOnUiThread
Explanation: runOnUiThread posts the block to the main thread.
7. Which dispatcher is best for CPU-intensive work like sorting a huge list?
- Dispatchers.Default
- Dispatchers.IO
- Dispatchers.Main
- Dispatchers.UI
Answer: A) Dispatchers.Default
Explanation: Default uses a pool sized to CPU cores.
8. Coroutines started in viewModelScope are cancelled when:
- The user scrolls
- The screen rotates
- The phone sleeps
- The ViewModel is cleared
Answer: D) The ViewModel is cleared
Explanation: viewModelScope survives rotation and is cancelled in onCleared.
9. Which is NOT a task to move off the main thread?
- Setting a TextView's text to a short string
- Decoding a large image
- Downloading a file
- Querying a large database
Answer: A) Setting a TextView's text to a short string
Explanation: Short UI updates belong on the main thread.
10. Music playback that continues with an ongoing notification should use a:
- Toast
- WorkManager job
- BroadcastReceiver
- Foreground service
Answer: D) Foreground service
Explanation: Foreground services perform user-noticeable ongoing work.
11. With Play App Signing, Google holds the:
- Debug keystore
- Source code
- App signing key, while the developer uses an upload key
- Developer's password
Answer: C) App signing key, while the developer uses an upload key
Explanation: Google re-signs delivered APKs with the app signing key.
12. The file that stores your release signing key is called a:
- Keystore (.jks)
- Gradle wrapper
- Bundle
- Manifest
Answer: A) Keystore (.jks)
Explanation: The keystore holds the private key and certificate.
13. R8 in release builds is used to:
- Sign the APK
- Create the keystore
- Shrink, optimise and obfuscate code and remove unused resources
- Upload to Play
Answer: C) Shrink, optimise and obfuscate code and remove unused resources
Explanation: R8 replaces ProGuard for shrinking and obfuscation.
14. The applicationId of a published app:
- Can be changed with every update
- Is the app's display name
- Must stay the same forever; changing it creates a different app
- Is optional
Answer: C) Must stay the same forever; changing it creates a different app
Explanation: Play identifies apps by their application ID.
15. A coroutine is best described as:
- A layout
- A lightweight, suspendable computation that does not block threads
- A database table
- A heavy operating-system thread
Answer: B) A lightweight, suspendable computation that does not block threads
Explanation: Coroutines suspend instead of blocking, so many can run on few threads.
16. WorkManager constraints can require that work runs only when:
- The device has a network connection or is charging
- The app is in landscape
- The screen is rotated
- A Toast is shown
Answer: A) The device has a network connection or is charging
Explanation: Constraints include network type, charging, battery not low, storage not low.
17. Which value must increase with every new version uploaded to Google Play?
- versionName
- applicationId
- versionCode
- minSdk
Answer: C) versionCode
Explanation: versionCode is an integer compared by Play to identify newer builds.
18. An ANR dialog appears when the main thread does not respond to input for about:
- 1 second
- 2 minutes
- 5 seconds
- 30 seconds
Answer: C) 5 seconds
Explanation: Input dispatch timeout is about 5 seconds.
19. Which Jetpack library is recommended for deferrable work that must run even after the app closes or the device restarts?
- WorkManager
- Navigation
- Room
- AppCompat
Answer: A) WorkManager
Explanation: WorkManager guarantees execution under constraints.
20. Two threads waiting for each other forever is called:
- ANR
- Fragmentation
- Race condition
- Deadlock
Answer: D) Deadlock
Explanation: Deadlock blocks both threads permanently.
21. The minimum interval of a periodic WorkManager request is:
- 1 hour
- 15 minutes
- 1 minute
- 1 day
Answer: B) 15 minutes
Explanation: PeriodicWorkRequest has a 15-minute minimum.
22. A Looper's job is to:
- Compile code
- Run a loop that takes messages from the MessageQueue and dispatches them
- Connect to Wi-Fi
- Loop animations
Answer: B) Run a loop that takes messages from the MessageQueue and dispatches them
Explanation: Each Looper processes its thread's message queue.
23. New apps on Google Play must be published as:
- ZIP files
- Android App Bundles (AAB)
- APK files only
- IPA files
Answer: B) Android App Bundles (AAB)
Explanation: AAB is mandatory for new apps since August 2021.
24. Which builder returns a result that can be awaited?
- post
- launch
- runOnUiThread
- async
Answer: D) async
Explanation: async returns a Deferred whose result is obtained with await().
25. A Handler is used to:
- Store preferences
- Post messages or runnables to a thread's message queue (e.g. delayed tasks)
- Draw layouts
- Sign APKs
Answer: B) Post messages or runnables to a thread's message queue (e.g. delayed tasks)
Explanation: Handlers work with Loopers and MessageQueues.
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Practise Threading and Publishing Android Applications MCQs
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