How do I create stubs for IO files to unit test in Java?

For a testing course assignment, I need to create unit tests for my already-coded system using JUnit. My system is heavily dependent on each other and it also writes/reads from a couple of text files on my disk. I realize I have to eliminate all dependancies to successfully unit test, I just don't know how to create stubs for Files.

Any help in code, tools or concepts is welcome