Introduction to Android: Architecture, Components & Features

App components are the essential building blocks of an Android app. Each component is an entry point through which the system or a user can enter your app. Some components depend on others.

What Is Android?

Android is an open-source mobile operating system developed by Google, primarily designed for touchscreen devices such as smartphones, tablets, smart TVs, wearables, and automotive systems.

Key Points

🔸 Based on Linux Kernel
🔸 Written mainly in Java, Kotlin, and C/C++
🔸 Apps run inside a sandboxed environment
🔸 Highly customizable by device manufacturers

Android Architecture (Layered Design)

Android follows a layered architecture, where each layer has a specific responsibility.

Android Architecture Layers (Top to Bottom)

1. Applications Layer

This is the topmost layer, visible to users.

Examples:

🔸 Phone
🔸 Messages
🔸 Camera
🔸 WhatsApp
🔸 Instagram
🔸 Chrome

Key characteristics:

🔸 Written using Java/Kotlin
🔸 Each app runs in its own process
🔸 Secure through application sandboxing

2. Application Framework

This layer provides APIs and system services used by applications.

Important components:

🔸 Activity Manager – Manages activity lifecycle
🔸 Window Manager – Manages windows and UI
🔸 Content Providers – Enables data sharing between apps
🔸 Notification Manager – Handles notifications
🔸 Resource Manager – Manages strings, layouts, and images

🔸 Developers interact mostly with this layer

3. Android Runtime (ART)

ART is responsible for running Android applications.

Key features:

🔸 Ahead-of-Time (AOT) compilation
🔸 Garbage collection
🔸 Memory optimization
🔸 Improved app performance

🔸 Replaced Dalvik Virtual Machine
🔸 Each app runs in its own runtime instance

4. Native Libraries

These libraries are written in C/C++ and provide low-level functionality.

Examples:

🔸 SQLite – Database management
🔸 OpenGL ES – Graphics rendering
🔸 WebKit – Web browser engine
🔸 Media Framework – Audio and video playback

🔸 Accessed through Android Framework APIs

5. Linux Kernel (Core Layer)

This is the foundation of the Android operating system.

Responsibilities:

🔸 Process management
🔸 Memory management
🔸 Device drivers
🔸 Power management
🔸 Security

🔸 Ensures hardware abstraction
🔸 Optimized Linux kernel for mobile devices

Core Android Application Components

Every Android application is built using four main components.

1. Activity

Represents a single screen with a user interface.

Examples:

🔸 Login screen
🔸 Dashboard screen

Key points:

🔸 Has a lifecycle (onCreate, onStart, onResume, etc.)
🔸 Managed by the Activity Manager

2. Service

Used to perform background operations without a user interface.

Examples:

🔸 Music playback
🔸 File uploads
🔸 Data synchronization

Types of services:

🔸 Foreground Service
🔸 Background Service
🔸 Bound Service

3. Broadcast Receiver

Listens for system-wide or application-level events.

Examples:

🔸 Battery low
🔸 Internet connectivity change
🔸 SMS received

Key characteristics:

🔸 Does not have a UI
🔸 Short-lived component

4. Content Provider

Used to share data between applications.

Examples:

🔸 Contacts
🔸 Media Store

Key points:

🔸 Uses URI-based access
🔸 Enforces permissions for data security

Android App Manifest (AndroidManifest.xml)

The Android Manifest file acts as the control center of an application.

It defines:

🔸 Application components
🔸 Required permissions
🔸 App name and icon
🔸 Minimum SDK version
🔸 Entry (launcher) activity

Example:

Key Android Features

1. Open Source

🔸 Developers can inspect and modify the source code
🔸 Encourages innovation and customization

2. Multitasking

🔸 Multiple applications can run simultaneously
🔸 Efficient memory and process management

3. Security

🔸 Application sandboxing
🔸 Permission-based access control
🔸 Secure inter-process communication

4. Hardware Support

🔸 Camera
🔸 GPS
🔸 Bluetooth
🔸 Sensors such as accelerometer and gyroscope

5. Rich UI and Customization

🔸 Material Design support
🔸 Custom themes
🔸 Smooth animations and transitions

6. Connectivity

🔸 Wi-Fi
🔸 Bluetooth
🔸 NFC
🔸 Cellular networks (4G and 5G)

Why Android Architecture Matters (Interview Point)

🔸 Clear separation of concerns
🔸 Better performance
🔸 High scalability
🔸 Strong security isolation
🔸 Easy maintenance and updates

Interview Tip:

Android architecture allows developers to build scalable, secure, and performance-optimized applications.

Quick Revision

🔸 Android – Open-source mobile operating system
🔸 Architecture – Layered software stack
🔸 Components – Activity, Service, Broadcast Receiver, Content Provider
🔸 Runtime – ART executes applications
🔸 Kernel – Manages hardware and memory
🔸 Features – Secure, customizable, multitasking