source code directory structure

root
  |-iabi
  |-art
  |-bionic  :google为android新做的类似glibc的库
  |-bootable
  |-build
  |-cts
  |-dalvik
  |-developers
  |-development
  |-device
  |-docs
  |-external    :第二方工具.注意google自有,所以不是第三方;非anrdoid 所有，所以不是第一方
  |-frameworks
  |-hardware
  |-libcore
  |-libnativehelper
  |-Makefile
  |-ndk
  |-out     : build out put files
  |-packages
  |-pdk
  |-prebuilts
  |-sdk
  |-system
  |-tools

------------------------------------------------
packages/app   : system\app\<*.apk> project
frameworks/base/core/java/android   : android api for android.jar android.*.*