I didn't understand the following sentence in an assignment: "In either case, the program must allow the user to specify the location of the database, ..." I solved the problem in the following matter: that the standalone client is allowed to choose a database and there is a hint on the mask to choose a local database. In my opinion it doesn't make sense that the network client can choose a database on the server computer. The RMI network client is in my opinion only interested in reserving hotel rooms.
You start the application with [<mode>] mode can be alone or server or nothing for the network client java -jar <path_and_filename> [<mode>]
I can't imagine that I need a GUI where the user can choose local mode or remote mode and the user can choose a database - file for the network client.