Android interview questions

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1. What is Android?

Answer: Android is an open-source, Linux-based operating system used primarily on mobile devices, such as smartphones and tablets. Developed by Google, it offers a unified approach to application development for mobile devices, meaning developers need to develop for Android, and their applications should be able to run on different devices powered by Android.

2. Describe the Android application architecture.

Answer: Android application architecture has several components such as:

  • **Activities** that represent a single screen with a user interface,

  • **Services** for background processing,

  • **Content Providers** for data management,

  • **Broadcast Receivers** for listening to system events,

  • All these components are glued together by the **AndroidManifest.xml** file that describes each component of the application and how they interact.

3. What are Activities in Android?

Answer: An Activity in Android is a single screen with a user interface. It's like a window or frame of Java. Starting from one activity, you can start another activity and send data to it using intents.

4. Explain the Activity lifecycle.

Answer: The Activity lifecycle includes seven methods that manage the lifecycle of an Activity:

  • `onCreate()`

  • `onStart()`

  • `onResume()`

  • `onPause()`

  • `onStop()`

  • `onRestart()`

  • `onDestroy()`

These methods create a cycle from the start of an activity to its end and help manage resources.

5. What are Intents?

Answer: Intents are messaging objects used to request an action from another app component. There are two types of intents in Android:

  • **Explicit Intents** specify the component to start by name.

  • **Implicit Intents** declare a general action to perform, allowing a component from another app to handle it.

6. What is a Fragment?

Answer: A Fragment represents a behavior or a portion of the user interface in an Activity. You can combine multiple fragments in a single activity to build a multi-pane UI and reuse a fragment in multiple activities.

7. Explain the concept of Services in Android.

Answer: A Service is an application component that can perform long-running operations in the background and does not provide a user interface. Services can run in the background even when the user is interacting with another application.

8. What are Broadcast Receivers?

Answer: Broadcast Receivers simply respond to broadcast messages from other applications or from the system itself. These messages can be anything from battery low warnings to app component communications.

9. What is a Content Provider?

Answer: A Content Provider manages access to a central repository of data. It is a standard interface that connects data in one process with code running in another process.

10. Explain the AndroidManifest.xml file.

Answer: The AndroidManifest.xml file contains information about your application that the Android system must know before the codes can be executed. This includes the package name, components like services, activities, broadcast receivers, content providers, etc., permissions, and the minimum level of the Android API that the application requires.

11. How do you persist data in Android?

Answer: Data in Android can be persisted using SharedPreferences, files (internal & external storage), SQLite databases, and Content Providers.

12. What is ANR in Android?

Answer: ANR stands for Application Not Responding, which is a dialog that appears to the user when an application has been unresponsive for a long period of time.

13. Explain AsyncTask in Android.

Answer: AsyncTask is used to perform background operations and publish results on the UI thread without having to manipulate threads and handlers.

14. What are the main components of an APK file?

Answer: The main components of an APK file include:

  • **DEX** files (compiled byte code),

  • **Resources** (images, strings, layouts etc.),

  • **Assets**,

  • **Native libraries**,

  • And the **AndroidManifest.xml**.

15. Describe how you can update the UI from a background thread.

Answer: The UI can be updated from a background thread using the Activity's runOnUiThread method, a Handler, or using AsyncTask.

16. What is the Android testing framework?

Answer: The Android testing framework includes instrumentation tools, unit tests, and UI tests to test Android applications. The framework provides hooks into the Android component and application lifecycle.

17. Explain the concept of Application class in Android.

Answer: The Application class in Android is the base class within an Android app that contains all other components such as activities and services. The Application object is created before any other application components.

18. What are Grad

le and Gradle files?

Answer: Gradle is an advanced build toolkit used to manage dependencies and other aspects of building Android applications. Gradle files are scripts where you define your settings and dependencies for Gradle in your project.

19. How do you ensure your Android app is accessible?

Answer: Ensure your app is accessible by using content descriptions for views, making UI elements accessible with touch gestures, testing with screen readers like TalkBack, and following the accessibility guidelines provided by Google.

20. What is a RecyclerView?

Answer: RecyclerView is a more advanced and flexible version of ListView that helps in displaying large datasets by recycling views that are no longer visible on the screen, thus improving performance.

21. What are Android App Widgets?

Answer: App Widgets are miniature application views that can be embedded in other applications (like the home screen) and receive periodic updates.

22. What is ADB?

Answer: ADB stands for Android Debug Bridge. It is a command-line tool that allows developers to communicate with an emulator instance or connected Android-powered devices for debugging and testing purposes.

23. Explain the use of the `Volley` library.

Answer: Volley is an HTTP library that makes networking for Android apps easier and faster, for making network requests, image loading, and caching.

24. What is Material Design?

Answer: Material Design is a comprehensive guide for visual, motion, and interaction design across platforms and devices introduced by Google, aiming to provide a consistent, intuitive experience across all device sizes.

25. How do you handle multi-threading in Android?

Answer: Multi-threading in Android can be handled using Java threads, AsyncTask, or using libraries like RxJava to manage complex asynchronous operations and event chains.

26. What is the use of the ConstraintLayout?

Answer: `ConstraintLayout` allows you to create large and complex layouts with a flat view hierarchy (no nested view groups). It's similar to RelativeLayout but more flexible and easier to use.

27. What is Doze Mode in Android?

Answer: Doze Mode is a power-saving feature introduced in Android 6.0 (Marshmallow) that defers background CPU and network activity for apps when the device is unused for long periods.

28. Explain Android Jetpack.

Answer: Android Jetpack is a suite of libraries, tools, and architectural guides that help developers follow best practices, reduce boilerplate code, and write code that works consistently across Android versions and devices.

29. What are the steps to optimize battery usage in an Android app?

Answer: Optimize battery usage by managing wake locks, using job scheduling tasks, optimizing network requests, using the AlarmManager sparingly, and testing with Battery Historian.

30. How can you use Kotlin in Android development?

Answer: Kotlin is fully supported for Android development, offering a concise, expressive, and safe programming language that can interoperate with Java and run on the JVM. You can use Kotlin to write new Android apps or gradually convert existing Java apps to Kotlin.

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