Do not use interrupt calls to notify threads that are accessing a database, because Derby will catch the interrupt call and close the connection to the database. Use wait and notify calls instead.
This will not happen in a client/server environment, but if you want your application to work in either environment it is good practice to follow this rule.
There are special considerations when working with more than one database thread in an application. See Working with multiple connections to a single database and Working with multiple threads sharing a single connection.