filesystems - Files.move(Path, Path) in Java -

by reading this tutorial, have come across part not quite clear me.

empty directories can moved. if directory not empty, move allowed when directory can moved without moving contents of directory.

i thoroughly understand empty directories can moved. second part of quote seems me little confusing. able express same concept in other words? in advance.

on unix systems, moving directory within same partition consists of renaming directory. in situation, method works when directory contains files.

this next sentence in link posted, provides example when possible use move if directory not empty.