Android ---Check System Version at Runtime（在软件运行时检查判断系统版本）

Android为我们提供了一个常量类Build，其中最主要是Build中的两个内部类VERSION和VERSION_CODES

VERSION表示当前系统版本的信息，其中就包括SDK的版本信息，用于成员SDK_INT表示；

对于VERSION_CODES在ＳＤＫ开发文档中时这样描述的，Enumeration of the currently known SDK version codes. These are the values that can be found in SDK. Version numbers increment monotonically with each official platform release.

在我们自己开发应用过程中，常常使用如下的代码形式判断运行新API还是旧的API:

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB)  {  // 包含新API的代码块 } else { // 包含旧的API的代码块 }

以下为版本号:

int	BASE	October 2008: The original, first, version of Android.
int	BASE_1_1	February 2009: First Android update, officially called 1.1.
int	CUPCAKE	May 2009: Android 1.5.
int	CUR_DEVELOPMENT	Magic version number for a current development build, which has not yet turned into an official release.
int	DONUT	September 2009: Android 1.6.
int	ECLAIR	November 2009: Android 2.0 Applications targeting this or a later release will get these new changes in behavior: The Service.onStartCommand function will return the new START_STICKY behavior instead of the old compatibility START_STICKY_COMPATIBILITY.
int	ECLAIR_0_1	December 2009: Android 2.0.1
int	ECLAIR_MR1	January 2010: Android 2.1
int	FROYO	June 2010: Android 2.2
int	GINGERBREAD	November 2010: Android 2.3 Applications targeting this or a later release will get these new changes in behavior: The application's notification icons will be shown on the new dark status bar background, so must be visible in this situation.
int	GINGERBREAD_MR1	February 2011: Android 2.3.3.
int	HONEYCOMB	February 2011: Android 3.0.
int	HONEYCOMB_MR1	May 2011: Android 3.1.
int	HONEYCOMB_MR2	June 2011: Android 3.2.
int	ICE_CREAM_SANDWICH	October 2011: Android 4.0.
int	ICE_CREAM_SANDWICH_MR1	December 2011: Android 4.0.3.
int	JELLY_BEAN	June 2012: Android 4.1.
int	JELLY_BEAN_MR1	Android 4.2: Moar jelly beans! Applications targeting this or a later release will get these new changes in behavior: Content Providers: The default value of android:exported is now false.