使用JAVA语言实现下列功能的系统 a)　　 系统能接受用户输入一个文件名，该文件名对应的文件A可能包含中文，英文字符，换行回车等字符。 b)　　 系统在确认用户输入的文件A存在后对文件A进行处理，生成另外一个文件B,要求文件B显式包含文件A的所有内容，并且不改变文件A中的已经有的内容。 c)　　 系统在文件A不存在的情况下，可以发现B中保留的A的内容被修改过。这种修改包括删除/增加A的某行信息，在A的内容中增加/删除/修改某个字符。-use JAVA following a function of the system) system will accept user input a name, the name of the paper document may contain A Chinese and English characters such as newline characters enter. B) System user input in identifying the existence of a document after document A pair of processed produce another document B, B requested documents Explicit document contains all the elements of A and A does not change the document has some content. C) A system in the document did not exist circumstances, it can be found B of A to retain the content has been modified. Such changes include the deletion / A increased to a certain line of information in the contents of A Increase / delete / change certain characters.