说明：  java中字符截取substring 　　public String substring(int beginIndex)返回一个新的字符串，它是此字符串的一个子字符串。该子字符串始于指定索引处的字符，一直到此字符串末尾。
(java in character interception substring public String substring (int beginIndex) returns a new string, which is a substring of this string. The substring begins at the specified index of the character, has been at the end of this string.)