WindowsFilenameTabCompleter.startsWithRoot() is implemented to treat strings containing :\ as absolute paths.

This does not handle UNC paths (network shares) which start with a double backslash. The rest of the path is also not sensitive to whether you use forward or backward slashes, so perhaps it should consider paths containing :/ as absolute too.

Are there situations where "new File(path).isAbsolute()" would not work?