android是什么

What is Android?
Android is a software stack for mobile devices that includes an operating system,middleware and key applications.The Android SDK provides the tools and APIs necessary to begin developing applications on the Android platform using the Java programming language.
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安卓是什么？
安卓是一个包含操作系统、中间件和关键应用的软件栈。

安卓二次开发套件提供了使用Java 编程语言在安卓平台上开发应用程序的工具和应用程序接口。

Features
Application framework enabling reuse and replacement of components
Dalvik virtual machine optimized for mobile devices
Integrated browser based on the open source WebKit engine
Optimized graphics powered by a custom2D graphics library;3D graphics based on the OpenGL ES1.0specification(hardware acceleration optional)
SQLite for structured data storage
Media support for common audio,video,and still image formats(MPEG4,H.264,MP3, AAC,AMR,JPG,PNG,GIF)
GSM Telephony(hardware dependent)
Bluetooth,EDGE,3G,and WiFi(hardware dependent)
Camera,GPS,compass,and accelerometer(hardware dependent)
Rich development environment including a device emulator,tools for debugging, memory and performance profiling,and a plugin for the Eclipse IDE
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功能特性：
使组件能够被重用和替换的应用程序框架。

为移动设备优化的戴尔维科虚拟机。

集成基于开源的Webkit引擎的浏览器。

特有二维图形库优化的二维图形；基于OpenGL ES1.0说明文档的三维图形（可选硬件加速）。

结构化数据存储利器SQLite数据库。

对日常声音、视频和各种图片格式媒体的支持。

GSM电话技术（须硬件支持）。

蓝牙、edge、3g和wifi（须硬件支持）。

摄像头、全球定位系统、指南针、加速计（须硬件支持）。

包含设备模拟器、调试工具、内存和表现配置和Eclipse插件的富开发环境。

Android Architecture
The following diagram shows the major components of the Android operatingsystem.Each section is described in more detail below.
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安卓构架
下图揭示安卓系统的主要组成部分。

后面每节都有更详细的描述。

Applications
Android will ship with a set of core applications including an email client,SMS program, calendar,maps,browser,contacts,and others.All applications are written using the Java programming language.
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应用
安卓内置包含电子邮件客户端、短消息系统程序、日历、地图、浏览器、通讯录等等的核心应用。

所有应用都是用java语言写的。

Application Framework
By providing an open development platform,Android offers developers the ability to build extremely rich and innovative applications.Developers are free to take advantage of the device hardware,access location information,run background services,set alarms,add notifications to the status bar,and much,much more.
Developers have full access to the same framework APIs used by the core applications.The application architecture is designed to simplify the reuse of components;any application can publish its capabilities and any other application may then make use of those capabilities(subject to security constraints enforced by the framework).This same mechanism allows components to be replaced by the user.
Underlying all applications is a set of services and systems,including:
A rich and extensible set of Views that can be used to build an application,including lists,grids,text boxes,buttons,and even an embeddable web browser
Content Providers that enable applications to access data from other applications (such as Contacts),or to share their own data
A Resource Manager,providing access to non-code resources such as localized strings,graphics,and layout files
A Notification Manager that enables all applications to display custom alerts in the status bar
An Activity Manager that manages the lifecycle of applications and provides a common navigation backstack
For more details and a walkthrough of an application,see the Notepad Tutorial.
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应用框架
通过提供一个开放的开发平台，安卓使开发者能够建立丰富而且有创造性的应用。

开发者可以自由地利用设备硬件、访问位置信息、运行后台服务、设定警报、在状态栏添加通知等等。

开发者对核心应用使用的框架应用程序接口有完全的访问权限。

应用构架被设计为简化组件重用；任何应用都能发布它的性能，而且这些性能可以被其他应用程序利用（在框架强制的安全限制之下）。

这种机制允许用户替换组件。

在所有的应用之下有一套服务和系统，包括：
一个丰富而且可扩展的外观。

它能用来建立一个包含列表、网格、文本框、按钮甚至内置网络浏览器的应用。

Content Provider们使一个应用能够访问另一个应用（比如通讯录）的数据或者分享自己的数据。

一个资源管理器为诸如本地化字符串、图片和布局文件等非代码资源提供访问。

一个通知管理器使所有应用能在状态栏显示自定义的警报。

一个活动管理器管理应用的生命周期并且提供了一个共同的导航记录栈。

欲知更多细节和应用攻略，请参看记事本教程。

Libraries
Android includes a set of C/C++libraries used by various components of the Android system. These capabilities are exposed to developers through the Android application framework.Some of the core libraries are listed below:
System C library-a BSD-derived implementation of the standard C system library (libc),tuned for embedded Linux-based devices
Media Libraries-based on PacketVideo's OpenCORE;the libraries support playback and recording of many popular audio and video formats,as well as static image files, including MPEG4,H.264,MP3,AAC,AMR,JPG,and PNG
Surface Manager-manages access to the display subsystem and seamlessly composites2D and3D graphic layers from multiple applications
LibWebCore-a modern web browser engine which powers both the Android browser and an embeddable web view
SGL-the underlying2D graphics engine
3D libraries-an implementation based on OpenGL ES1.0APIs;the libraries use either hardware3D acceleration(where available)or the included,highly optimized3D software rasterizer
FreeType-bitmap and vector font rendering
SQLite-a powerful and lightweight relational database engine available to all applications
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库
安卓包含一套被许多安卓系统组件使用的C/C++库。

这些性能通过安卓应用框架暴露在开发者眼前。

部分核心库如下所示：
c系统库。

为基于嵌入式linux设备调整的标准C系统库的BSD衍生补集。

媒体库。

基于PacketVideo的OpenCORE；该库支持许多音频、视频的回调和录制。

外表管理器。

管理显示子系统的访问和无缝结合多个应用的二维三维图片层。

LibWebCore。

一个现代网络浏览器引擎。

SGL。

三维库。

FreeType。

位图和矢量字表现。

SQLite。

一个强大的轻量级关系数据库引擎。

Android Runtime
Android includes a set of core libraries that provides most of the functionality available in the core libraries of the Java programming language.
Every Android application runs in its own process,with its own instance of the Dalvik virtual machine.Dalvik has been written so that a device can run multiple VMs efficiently.The Dalvik VM executes files in the Dalvik Executable(.dex)format which is optimized for minimal memory footprint.The VM is register-based,and runs classes compiled by a Java language compiler that have been transformed into the.dex format by the included"dx"tool.
The Dalvik VM relies on the Linux kernel for underlying functionality such as threading and low-level memory management.
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安卓运行时
安卓包含一套核心库。

这些库提供大多数java语言核心库里一样的功能。

每个安卓应用在各自的Dalvik虚拟机实例里运行自己的进程。

一个设备可以运行多个dalvik虚拟机。

dalvik虚拟机执行为小内存优化的扩展名为“.dex”的dalvik可执行文件。

虚拟机是基于寄存器的，运行java语言编译器dx工具编译成dex格式的类。

dalvik虚拟机依靠linux内核实现基本功能如进程和低级内存管理。

Linux Kernel
Android relies on Linux version2.6for core system services such as security,memory management,process management,network stack,and driver model.The kernel also acts as an
abstraction layer between the hardware and the rest of the software stack.
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linux内核
安卓依靠2.6版的linux内核实现核心系统服务如安全、内存管理、进程管理、网络栈和驱动模型。

内核也作为硬件和软件栈之间的抽象层。