You must install the Android SDK before you can develop apps.
Windows、Intel-based Mac OS X、i386-based Linux operating systems.
下载并解压后，更新PATH环境变量。
下载和安装SDK的前提条件：
Android SDK支持一下操作系统：
（1）Windows XP（32-bit），Vista（32- or 64-bit），or Windows 7（32- or 64-bit）.
（2）Mac OS X 10.5.8 or later（x86 only）
（3）Linux..........
JDK 6 or JDK 7
Apache Ant：1.8 or later so that you can build Android projects from the command line.
It is recommanded that you rename android-sdk-windows to android to avoid a potential emulator crash when attempting to run an app from within Eclipse.
To complete the installation, add the tools and platform-tools subdirectories to your PATH environment variable.