in order to be able to select directories, but it only allows directory selection. Not setting it only allows file selection. I wish to be able to select either a file OR a directory, which I haven't found a way to do with FileDialog.
Yes Sir. While it has the look and feel of Aqua, it does not have the behaviour ("column view") to which so many Mac users are accustomed. This is why it is (apparently) fairly common for Mac-conscious developers to detect the System OS, and use FileDialog for Macs, otherwise use JFileChooser, such as this: