XPath or XQuery

Hello all.
I´m new at XQuery and XPath and I´m not clear about how it works.

I have a set of xml documents in a directory and I need to select the documents that satisfy a condition from a Java application. For example, to select all documents whose node Name was 'John'. I don´t want to use any kind of database. 
So, is it possible to make this query with XPath?. Can only XPath use to make a query to one document or can it make querys to a set of documents?. Should I use XQuery?.
Thanks in advance. 

 Noemí