Android OS: A Deep Dive into the Android Software Stack PDF

what Android isn't: 1. Not a Java ME implementation: Android apps are written using the Java programming language, but they don’t run on a Java ME (Mobile Edition) virtual machine. Regular Java programs won’t work directly on Android. 2. Not part of certain mobile standards organizations: Androi...

what Android isn't: 1. Not a Java ME implementation: Android apps are written using the Java programming language, but they don’t run on a Java ME (Mobile Edition) virtual machine. Regular Java programs won’t work directly on Android. 2. Not part of certain mobile standards organizations: Android uses an open-source Linux kernel, but it’s not directly tied to organizations like the Linux Phone Standards Forum (LiPS) or the Open Mobile Alliance (OMA). These organizations have similar goals, but Android’s approach is broader, covering more areas. 3. Not just an application layer: While Android has an application layer, it’s more than that. The term “Android” refers to the entire software stack. This includes not only the apps but also the operating system and the programming tools. 4. Not a single mobile phone handset: Android provides a design that manufacturers can use, but there isn’t just one “Android phone.” Instead, Android is made to work on various devices from different manufacturers. 5.Android is not Google's answer to the iPhone: The iPhone is a completely closed system (both hardware and software) made by a single company, Apple. In contrast, Android is an open-source software platform supported by the Open Handset Alliance (OHA). It’s designed to work on any device that is compatible, not just a single phone made by one company. what Android is and what it includes What is Android? Google’s Andy Rubin described Android as the first truly open and complete platform for mobile devices. It includes everything needed to run a phone—like the operating system, user interface, and applications—without the restrictions that other platforms have. Today, Android has grown beyond just mobile phones. It’s also used on tablets, TVs, and other devices. Android as an Ecosystem: Android can be thought of as a combination of three main components: 1. A free, open-source operating system for devices like smartphones and tablets. 2. A development platform that lets developers create applications. 3. Devices that run the Android OS and the apps built for it. What makes up Android? Android consists of several important parts: 1. Compatibility Definition Document (CDD) and Compatibility Test Suite (CTS): These ensure that any device that wants to run Android meets the required standards. 2. Linux Kernel: This is the core of the Android operating system. It handles interactions with the hardware, manages memory, and controls processes, all optimized for mobile and embedded devices. 3. Open-source Libraries: Includes tools for app development like SQLite (for databases), WebKit (for browsing), OpenGL (for graphics), and a media manager. 4. Runtime Environment: Android apps run on the Dalvik Virtual Machine (VM), which is designed to be lightweight and efficient for mobile devices. It also includes core libraries for Android-specific functions. 5. Application Framework: Provides tools and system services to apps, such as managing windows, accessing location data, databases, phone features, and sensors. 6. User Interface Framework: The system used to display and manage apps on the device. 7. Core Pre-installed Apps: Android comes with essential apps already installed, like messaging, phone, and browser apps. Native Android Applications: What comes preinstalled on Android devices? Most Android devices come with a set of built-in apps that are part of the Android Open Source Project (AOSP). These typically include: Email client: For sending and receiving emails. SMS management: For text messaging. PIM suite (Personal Information Management): Includes a calendar and contacts list. Web browser: Based on WebKit for browsing the internet. Music player and picture gallery: For playing music and viewing photos. Camera and video recorder: To take photos and videos. Calculator: For basic math operations. Home screen: The main interface you see when you unlock your phone. Alarm clock: For setting alarms and reminders. Additional Google apps (often found on Android devices) Many Android phones also come with Google’s proprietary apps, which are not part of the open-source project but are commonly included: Google Play Store: To download apps, games, and content. Google Maps: Includes StreetView, turn-by-turn navigation, satellite view, and real-time traffic updates. Gmail: For managing emails with a Google account. Google Talk (now Google Chat): For instant messaging. YouTube: To watch and upload videos. Customization by manufacturers Because Android is open-source, companies that build Android devices can customize the user interface and include their own apps. This flexibility is why different Android phones can look and feel different even though they run on the same underlying system. Android SDK (Software Development Kit) Features: Why is Android great for developers? The real strength of Android is its APIs (Application Programming Interfaces). These allow developers to create apps that can integrate ideal with the phone's built-in features, making them feel just as integrated as the apps that come preinstalled on the device. Key Features of the Android SDK: 1. Support for various network types: Works with GSM, 3G, 4G, and LTE networks for making calls, sending SMS, or transferring data. 2. Location-based services: Provides comprehensive tools for using GPS and network-based methods to detect the device’s location. 3. Maps and navigation integration: Includes APIs to integrate maps directly into apps, making it easy to create navigation or location-aware applications. 4. Wi-Fi and peer-to-peer connections: Allows access to Wi-Fi hardware for internet and peer-to-peer connections. 5. Multimedia support: Full control over media playback and recording, including access to the camera and microphone.Supports various audio, video, and image formats. 6. Sensor hardware support: APIs for accessing sensors like accelerometers, compasses. 7. Bluetooth and NFC capabilities: Includes support for Bluetooth and NFC (Near Field Communication) for device- to-device data sharing. 8. Inter-process communication (IPC): Supports message passing between different apps or processes for efficient communication. 9. Shared data and social integration: Provides access to shared contacts, calendar, social networks, and multimedia data for integration into apps. 10. Background services and processes: Supports apps that run in the background, like music players or data sync services. 11. Home-screen widgets and live wallpapers: Allows developers to create interactive widgets and dynamic wallpapers. 12. Web browser support: Includes an integrated, open-source HTML5 browser based on WebKit. 13. Graphics support: Optimized for 2D and 3D graphics with libraries for hardware-accelerated graphics. 14. Reusable application components: Encourages developers to reuse and replace parts of existing apps, making development more efficient. These features make Android a powerful and flexible platform for creating a wide range of apps, from simple utilities to complex, integrated solutions. Android SDK Features and Capabilities: 1. Access to Hardware: APIs for hardware like camera, GPS, and sensors are provided. This means developers can easily access device hardware without worrying about compatibility across different devices. 2. Data Transfers Using Wi-Fi, Bluetooth, and NFC: Android supports data sharing between devices using Bluetooth, Wi-Fi Direct. You can create apps that connect and transfer data between devices. 3. Maps, Geocoding, and Location Services: Maps integration allows you to include Google Maps in your apps. Location-based services use GPS or network-based methods to find the device's position.Geocoding APIs let you convert addresses to map coordinates or get addresses from coordinates. 4. Background Services: Android lets you run apps or services in the background, even when not actively visible to the user. This is useful for apps like music players or data syncing. 5. SQLite Database for Data Storage: Android includes a lightweight SQLite database for storing app data efficiently. 6. Shared Data and Inter-Application Communication: Intents allow apps to send messages or requests to other apps (like opening a web link or sharing a photo). 7. Widgets and Live Wallpaper: You can create widgets and live wallpapers that display dynamic information directly on the home screen, making it easier for users to interact with your app without opening it. 8. Extensive Media Support and 2D/3D Graphics: Android supports 2D and 3D graphics using libraries like OpenGL. It includes support for popular media formats such as MPEG4, H.264, MP3, AAC, JPG, and GIF. 9. Cloud to Device Messaging (C2DM): C2DM (Cloud to Device Messaging) allows you to send real-time notifications or updates from your server to a user’s device, keeping your app connected without draining the battery. 10. Optimized Memory and Process Management: Android uses a virtual machine (VM) to manage memory and kill processes when needed to free up resources. The app the user is currently interacting with gets the highest priority, while others may be stopped to optimize performance. Android Software Stack: What is the Android Software Stack? The Android software stack is a set of software components organized into layers. It is built on a Linux kernel and includes libraries, a runtime environment, an application framework, and applications. Each layer has a specific function to make the Android operating system work efficiently on devices. Key Layers of the Android Software Stack: 1. Linux Kernel: Core Services: Manages hardware drivers, processes, memory, security, networking, and power. Provides an abstraction layer between the device hardware and the rest of the software stack. Uses Linux kernel version 2.6 to handle low-level system operations. 2. Libraries: These are C/C++ libraries that sit above the Linux kernel. Includes: Media library: For playing audio and video files. Surface Manager: Manages display and rendering of user interface elements. Graphics libraries: Provides support for 2D (SGL) and 3D (OpenGL) graphics. SQLite: A lightweight database engine used for local data storage. SSL and WebKit: Used for web browsing and secure internet communications. 3. Android Runtime: This is the core environment that runs Android apps and makes an Android device different from other Linux-based systems. It consists of: Core Libraries: These are similar to Java libraries but are designed specifically for Android. Dalvik Virtual Machine (VM): A register-based VM optimized to run multiple apps efficiently. It uses the Linux kernel for memory management and process control. 4. Application Framework: Provides a set of classes that developers use to build Android applications. Handles the user interface, hardware access, and application resources. Offers system services like window management, location services, and content providers. 5. Application Layer: This is where all Android apps (both native and third-party) live. These applications are built using the same API libraries provided by the Android framework. Apps in this layer run within the Android runtime environment using the available classes and services. What Comes in the Box The Android SDK includes everything you need to start developing, testing, and debugging Android applications: The Android SDK (Software Development Kit) is a collection of tools and resources for developers to create Android applications. 1. Android APIs: ○ The core of the SDK, these are the same libraries Google uses to create native Android apps. These APIs provide access to Android's features and functions, allowing developers to build applications. 2. Development Tools: ○ The SDK includes tools for compiling, debugging, and turning Android source code into executable applications. 3. Android Virtual Device (AVD) Manager and Emulator: ○ The Android emulator simulates a mobile device, allowing you to test and see how your app looks and behaves on a real device. It runs within an Android Virtual Device (AVD) that mimics different hardware configurations. The emulator is a great environment for testing since it's hardware-neutral. 4. Full Documentation: ○ The SDK comes with detailed reference materials explaining how each API package and class works. The documentation also includes guides on best practices, the fundamentals of Android development, and in-depth information on framework topics. 5. Sample Code: ○ The SDK provides sample applications and programs that demonstrate Android capabilities. These samples help you learn how to use specific API features and build your own apps. 6. Online Support: ○ Android has a large, active developer community. Google Groups and Stack Overflow are great resources for asking questions and finding answers. These forums offer advice from experienced developers, as well as input from Google's engineering team. Android Architecture android architecture or Android software stack is categorized into five parts: 1. linux kernel 2. native libraries (middleware), 3. Android Runtime 4. Application Framework 5. Applications 1) Linux kernel It is the heart of android architecture that exists at the root of android architecture. Linux kernel is responsible for device drivers, power management, memory management, device management and resource access. 2) Native Libraries On the top of linux kernel, their are Native libraries such as WebKit, OpenGL, FreeType, SQLite, Media, C runtime library (libc) etc. The WebKit library is responsible for browser support, SQLite is for database, FreeType for font support, Media for playing and recording audio and video formats. 3) Android Runtime In android runtime, there are core libraries and DVM (Dalvik Virtual Machine) which is responsible to run android application. DVM is like JVM but it is optimized for mobile devices. It consumes less memory and provides fast performance. 4) Android Framework On the top of Native libraries and android runtime, there is android framework. Android framework includes Android API's such as UI (User Interface), telephony, resources, locations, Content Providers (data) and package managers. It provides a lot of classes and interfaces for android application development. 5) Applications On the top of android framework, there are applications. All applications such as home, contact, settings, games, browsers are using android framework that uses android runtime and libraries. Android runtime and native libraries are using linux kernal. Types of Android Application: 1. Foreground Applications These apps are useful only when they are actively in use (visible to the user). When they are not in the foreground, they are often paused or suspended. Characteristics: Highly interactive and require the user's full attention. Typically do not run in the background when the user is not interacting with them. Examples: Games: Such as Candy Crush, PUBG, where user interaction is constant. 2. Background Applications These apps do most of their work in the background with minimal user interaction. Once configured, they generally run without the need for the user to open them frequently. Characteristics Typically run services that work without direct user input. Mostly stay hidden until they need to notify the user or require configuration. Examples: Call screening apps: Automatically block unwanted calls. Alarm clocks: Work in the background to notify the user at set time. 3. Occasionally Applications These are versatile applications that have both foreground and background functionalities. They might need user interaction occasionally but can perform tasks in the background as well. Characteristics: Can function as a foreground app when the user interacts with it but also perform significant background tasks. Balance between foreground interaction and background processing. Examples: Media players: Like Spotify or YouTube Music, where users may interact to select songs but also let them play in the background. Email clients: Such as Gmail, which fetch emails in the background and notify the user when a new message arrives. News apps: Like Google News, which update content in the background and notify users of breaking news. 4. Widgets and Live Wallpapers These are specialized applications that don't have a typical user interface. Instead, they are represented as home-screen widgets or live wallpapers, providing information or interaction directly on the user's home screen. Characteristics: Minimal user interaction; primarily display data or visual content. Continuously update content based on background processes (e.g., weather widgets). Examples: Widgets: Weather updates, calendar events, or stock tickers displayed directly on the home screen. Live Wallpapers: Animated backgrounds that react to user actions or change over time. ---