Questions for Android Engineer Interview

Question:

What is the difference between implicit and explicit Intents in Android?

Answer:

In Android, Intents are used for communication between components of the app, such as starting activities, services, or broadcasting messages. There are two main types of Intents: explicit and implicit. Here’s a breakdown of the differences:

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1. Explicit Intent:

• Definition: An explicit intent explicitly specifies the target component (usually an Activity, Service, or BroadcastReceiver) by providing the exact class name.

• Usage: Used when you know exactly which component to start (i.e., you specify the name of the target class directly).

• Example: If you want to start a specific activity within your app, you would use an explicit intent to target that activity by its class name.

  Code Example:

  Intent intent = new Intent(MainActivity.this, SecondActivity.class);
  startActivity(intent);

  • Here, you are explicitly stating that you want to start SecondActivity from MainActivity.

• Key Points:

  • The component to be invoked is explicitly defined.
  • It is used within an app when there is a direct reference to the target component.
  • Example use cases: starting another activity, starting a service, or sending a broadcast within the same app.

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2. Implicit Intent:

• Definition: An implicit intent does not specify the target component directly. Instead, it declares an action to be performed, and the system determines which component is best suited to handle that action based on the intent filters.

• Usage: Used when you want to allow other apps or components to handle the intent. The system looks for a component that can handle the action, often using intent filters defined in the manifest.

• Example: If you want to open a webpage or send an email, you don’t specify which app to use; instead, you use an implicit intent that specifies the action (e.g., ACTION_VIEW for opening a webpage).

  Code Example:

  Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse("https://www.example.com"));
  startActivity(intent);

  • Here, you are using an implicit intent to open a URL. The system will choose the appropriate app (e.g., a browser or web view) to handle this request.

• Key Points:

  • The component is not explicitly specified. The system chooses which component to use based on the action and data.
  • It can be used for inter-app communication.
  • Example use cases: opening a web page, sending an SMS, sharing content, opening a map, or taking a picture.

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Summary of Differences:

Feature	Explicit Intent	Implicit Intent
Target Component	Specifies a specific component (e.g., activity, service).	Does not specify a target component.
Use Case	Used when the target component is known.	Used when the action is generic and handled by any suitable app.
Action	Directly specifies the class of the target component.	Specifies an action (e.g., view, send) and the system resolves it.
Example	Intent intent = new Intent(MainActivity.this, SecondActivity.class);	Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse("http://example.com"));

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When to Use Each:

• Use Explicit Intents:

  • When starting a specific component within your own app.
  • When you know the exact class you want to interact with (e.g., to open a specific activity or start a service).

• Use Implicit Intents:

  • When you want to perform an action (e.g., view a URL, send an email, take a photo) and are open to allowing any app that can handle that action to do so.
  • Useful for inter-app communication, where the system will decide which app can handle the intent based on intent filters.

  Question:

What are the major components of Android architecture?

Answer:

Android architecture is a complex stack that consists of several layers, each with distinct responsibilities for how the system works. Below are the major components of the Android architecture:

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1. Application Layer:

This is the topmost layer where Android apps reside. Applications run on top of the Android operating system and interact with the various Android services and components.

• Key Components:
  • Activities: User interface components that interact with the user.
  • Services: Background tasks that run without a UI.
  • Broadcast Receivers: Handle system-wide broadcast messages (e.g., battery low, Wi-Fi status change).
  • Content Providers: Used to manage and share data between applications.

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2. Application Framework Layer:

This layer provides high-level services for building Android applications. It includes a rich set of APIs and system services that manage core functionality like user interface, location, telephony, and more.

• Key Components:
  • Activity Manager: Manages the lifecycle of activities and keeps track of what happens when an app starts, stops, or switches.
  • Content Providers: Handle data access and sharing between apps.
  • Resource Manager: Provides access to various resources (like strings, images, and layouts) in the application.
  • Notification Manager: Manages notifications shown to users.
  • Package Manager: Manages installed apps, their metadata, and app installation and updates.
  • Telephony Manager: Manages phone-related services like calling, SMS, and network status.
  • Location Manager: Handles location-based services such as GPS, Wi-Fi positioning, etc.
  • Window Manager: Manages the placement and display of UI elements on the screen.

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3. Android Runtime (ART) and Dalvik Virtual Machine (DVM):

In the Android runtime layer, the apps are executed. Originally, Android used the Dalvik Virtual Machine (DVM), but now it uses the Android Runtime (ART).

• ART: ART is the new runtime for Android that replaces DVM, providing improved performance, better memory management, and more efficient app execution. ART uses Ahead of Time (AOT) compilation for converting app code into machine code.

• Key Components:

  • Dalvik Virtual Machine (DVM): An older VM for executing Android applications.
  • Android Runtime (ART): The modern runtime that runs apps in a more efficient manner.
  • JNI (Java Native Interface): Used to call C or C++ code from Java (native code interaction).

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4. Libraries Layer:

This layer contains a set of native libraries used by Android applications and services. These libraries are written in C/C++ and provide low-level functionality to Android.

• Key Libraries:
  • SQLite: A lightweight, relational database for storing app data.
  • OpenGL ES: A graphics API for rendering 2D and 3D graphics.
  • WebKit: A web browser engine used for rendering web pages.
  • Surface Manager: Manages the display of graphical content on the screen.
  • Media Framework: Supports audio, video, and image handling.
  • FreeType: A font rendering library.
  • SSL: Provides support for secure network connections.

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5. Linux Kernel Layer:

At the lowest level, the Linux kernel forms the foundation of the Android operating system. It is responsible for managing low-level system resources such as memory, processes, and hardware.

• Key Components:
  • Linux Kernel: Provides basic operating system functionality (memory management, process management, device drivers, etc.).
  • Hardware Abstraction Layer (HAL): A set of interfaces that provide access to hardware features like camera, audio, sensors, etc.
  • Security: Android’s security model (such as user permissions) is built on top of the Linux kernel.

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Summary of the Android Architecture Components:

Layer	Description	Key Components
Application Layer	Contains Android apps and core components (activities, services, broadcast receivers, etc.).	Activities, Services, Broadcast Receivers, Content Providers
Application Framework	Provides high-level APIs for Android app development.	Activity Manager, Content Providers, Notification Manager, Package Manager, etc.
Android Runtime (ART)	Runs apps and provides a runtime environment (ART/DVM).	ART, Dalvik VM (older), JNI (Java Native Interface)
Libraries Layer	Contains native libraries providing low-level functionality.	SQLite, OpenGL ES, WebKit, Media Framework, SSL, FreeType
Linux Kernel	Provides low-level system services, including memory management, device drivers, and hardware access.	Linux Kernel, Hardware Abstraction Layer (HAL), Security

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Conclusion:

Android architecture is designed to provide a rich, flexible, and powerful platform for mobile application development. The architecture’s layered approach ensures that Android apps can interact with hardware, system services, and native libraries efficiently while being isolated from the complexities of the operating system.

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