What:由函数Uri.parse()想到的

该函数的原型是:

    public static Uri parse(String uriString)

从数据类型上说：该函数通过解析一个字符串型而生成一个Uri实例

uriString满足：an RFC 2396-compliant, encoded URI，至于rfc可查阅http://www.ietf.org/rfc/rfc2396.txt

Uri类：Immutable URI reference. A URI reference includes a URI and a fragment, the component of the URI following a '#'. Builds and parses URI references which conform to   RFC 2396.

URL和URN都是URI的子集