What is Android?

Android is an operating system, middleware, and key application.ProgramSoftware set. The android SDK provides necessary tools and APIs for developing applications using Java on the Android platform.

 

Android platform features:

1. Application Framework:Provides reusable and replaceable components.
2. Davlik virtual machine:Virtual machines optimized for mobile devices.
3. Built-in browser:WebKit-based built-in browser.
4. Optimized graphic processing:Supports custom 2D graphics libraries and 3D graphics libraries based on OpenGL ES 1.0 (hardware acceleration)
5. SQLite:Lightweight databases for structured data storage.
6. Multimedia support:Supports common audio, video, and static image formats (mpeg3, H.264, MP3, AAC, Amr, JPG, PNG, and GIF)
7. GSM call(Depends on hardware)
8. Bluetooth, edge network, 3G, and WiFi(Depends on hardware)
9. Complete development environment:It includes simulators, debugging tools, memory and performance analysis, and Android plug-in ADT on Eclipse.

Android architecture:
The main components of Android are displayed, and each layer is described in more detail below.

 

Android applications:

Android included the e-mail client, SMS application, calendar, MAP, communication, and other core application sets. All applications are written in Java.

 

Android Application Framework:

By providing an open development platform, developers can build rich and creative applications. Developers can freely use the hardware of devices, access local information, run background services, Set alarms, and add prompts on the status bar.

Developers can access the android API. adnroid application framework like android core applications to simplify Component reuse. Any application can publish its functional blocks, and any other application can use these functional blocks (the security access restrictions of the framework must be observed ). This application reuse mechanism allows the component to be replaced by the user program.

All of the following applications are composed of a series of services and system functions, including:

1. A rich and scalable view (Views) that can be used to build an application interface. Including lists, grids, text boxes, buttons, and even an embedded web browser.
2. Content Providers (content providers) provide the ability to share data. Applications can access data (such as contacts) of other applications or share their own data.
3. A resource manager class that providesCodeData capabilities, such as local character length, images, and layout files)
4. A notification manager. Applications can display customer notification messages in the status bar.
5. An activity Manager manages the lifecycle of an application and provides common failover functions.

Android Library:

Android contains a C/C ++ library used by different components in the Android system. These libraries are provided to developers after being encapsulated by the Android Application Framework. Here are some major core libraries:

1. System C Library: a standard system C library (libc) inherited from BSD. libc is a C Library specially designed for Embedded Linux devices.
2. Media Library: opencres Based on packetvideo's. This Library supports recording and recording many popular audio and video formats, as well as static image files, including mpeg3 and H. 264, MP3, AAC, Amr, JPG, and PNG.
3. Surface MANAGER: manages display subsystems and provides seamless connections between 2D and 3D layers for multiple applications.
4. Libwebcore: The latest web browser engine that supports Android browsers and embedded web views.
5. SGL: a built-in 2D graphics engine.
6. 3D libraries: a 3D Library Based on OpenGL ES 1.0 APIs. This library can be accelerated using 3D hardware (if available) or with highly optimized 3D software.
7. FreeType: Display of Bitmap and Vector Fonts.
8. SQLite: a lightweight relational database available for all applications.

Android Runtime Library:

Android contains a core library that provides JavaProgramming LanguageMost features of the core library.

Each Android Application runs in its own process and has an independent davlvik Virtual Machine instance. Dalvik is designed to efficiently run multiple VMS instances at the same time. The Dalvik virtual machine executes the Dalvik executable file (suffixed with. Dex), which is optimized for small memory. The virtual machine is for registers. Classes running on the virtual machine are compiled by the Java compiler and converted to. Dex format by the android DX tool.

The Dalvik virtual machine depends on some features of the Linux kernel, such as the thread mechanism and the underlying memory management mechanism.

 

Linux Kernel:
Android is based on the linux2.6 kernel and provides some core system services through the Linux kernel, such as security, memory management, process management, network protocol stack, and driver module. This kernel also serves as the hardware abstraction layer between hardware and software.