SDK 的版本是： http://dl.google.com/android/android-sdk_r17-linux.tgz
参考 http://developer.android.com/sdk/exploring.html
目录：
SDK：
- build-tools
- platforms
- platform-tools
- api
- api-versions.xml
- api-versions.xml
- adb
- fastboot
- NOTICE.txt
- source.properties
- api
- tools
- ant
- apps
- lib
- proguard
- support
- templates
- adb_has_moved.txt
- android
- ddms
- dmtracedump
- draw9patch
- emulator
- emulator64-arm
- emulator64-mips
- emulator64-x86
- emulator-arm
- emulator-mips
- emulator-x86
- etc1tool
- hierarchyviewer
- hprof-conv
- jobb
- lint
- mksdcard
- monitor
- monkeyrunner
- NOTICE.txt
- source.properties
- sqlite3
- traceview
- uiautomatorviewer
- zipalign
<sdk>/build-tools/
tools目录里面包含了重要的编译工具，比如aapt、aidl、逆向调试工具dexdump和编译脚本dx。
<sdk>/platform/
存放Android SDK Platforms平台相关文件，包括字体、res资源、皮肤、模板等
platforms是每个平台的SDK真正的文件，里面会根据APILevel划分的SDK版本，这里就以Android2.2来说，进入后有一个android-8的文件夹，android-8进入后是Android2.2SDK的主要文件，其中ant为ant编译脚本，data保存着一些系统资源，images是模拟器映像文件，skins则是Android模拟器的皮肤，templates是工程创建的默认模板，android.jar则是该版本的主要framework文件.
<sdk>/platform-tools/
Contains platform-dependent tools for developing and debugging your application.
These tools support the latest features of the Android platform and are typically updated only when a new platform becomes available.
These tools are always backward compatible with older platforms, but you must be sure that you have the latest version of these tools when you install a new SDK platform.
<sdk>/tools/
Contains tools for debugging and testing, plus other utilities that are required to develop an app.
If you've just installed the SDK starter package, then you already have the latest version of this package.
Make sure you keep this up to date.
ddms用于启动Android调试工具draw9patch则是绘制android平台的可缩放png图片的工具
sqlite3可以在PC上操作SQLite数据库
monkeyrunner则是一个不错的压力测试应用，模拟用户随机按键
mksdcard则是模拟器SD映像的创建工具，
emulator是Android SDK模拟器主程序
traceview作为android平台上重要的调试工具。