Android is an open-source operating system developed by Google, primarily used in mobile devices such as smartphones, tablets, smart TVs, and wearables. It is based on the Linux kernel and supports both native and managed application development.
Key Components of Android Architecture
1. Linux Kernel
- Provides core system services such as process management, memory management, and security.
- Hardware abstraction and device driver management.
2. Hardware Abstraction Layer (HAL)
- Interfaces between the device hardware and the Android runtime.
- Standardizes access to device capabilities.
3. Android Runtime (ART)
- Executes Android apps, replacing the older Dalvik VM.
- Uses Ahead-Of-Time (AOT) compilation for better performance.
4. Libraries
- Includes C/C++ libraries for core functionality (e.g., SQLite, SSL, WebKit).
- Exposed to developers through the Android framework.
5. Application Framework
- Java/Kotlin APIs used to build Android applications.
- Components: Activity Manager, Content Providers, Notification Manager, etc.
6. Applications
- User-installed or system apps (e.g., dialer, browser, messaging).
- Built with components like Activities, Services, Broadcast Receivers, and Content Providers.
Android App Components
| Component | Description |
|---|---|
| Activity | UI component representing a single screen (e.g., login page). |
| Service | Background component performing long-running tasks (e.g., music playback). |
| Broadcast Receiver | Responds to broadcast messages (e.g., battery low notification). |
| Content Provider | Shares data between applications (e.g., contacts, files). |
Android Development Tools
| Tool | Purpose |
|---|---|
| Android Studio | Official IDE, supports Java, Kotlin, and C++. |
| ADB (Android Debug Bridge) | CLI for device communication. |
| Gradle | Build automation tool used to compile and package apps. |
| AVD Manager | Creates Android virtual devices for testing. |
| Android SDK | Libraries and tools to build Android apps. |
Android Programming Languages
- Java: Original language of Android development.
- Kotlin: Modern, concise alternative to Java, now officially preferred.
- C/[[C++]]: Used with the NDK for performance-critical tasks.
App Distribution and Publishing
- Apps are typically distributed via Google Play Store or other marketplaces (e.g., Amazon Appstore).
- Apps are packaged as
.apkfiles (Android Package). - Requires digital signing and adherence to Google’s publishing guidelines.
Android App Lifecycle (Simplified)
Activity Lifecycle
onCreate() → onStart() → onResume() → [App Running] → onPause() → onStop() → onDestroy()Service Lifecycle
onCreate() → onStartCommand() → [Running] → onDestroy()Managing lifecycle events properly is critical for performance, stability, and battery usage.