A DESCRIPTION OF THE REQUEST :
The current JavaFX file dialogs don't support FILES_AND_DIRECTORIES mode that the good old JFileChooser did support.

This is a 2017 refresh for this old RFE from 2012:
https://bugs.openjdk.java.net/browse/JDK-8102208

Previously, it was "Won't Fix" because of Windows XP and GTK 2. Since Java 9 has dropped support for Windows XP and now supports GTK 3 on Linux it might be time to reevaluate this request once again.

JUSTIFICATION :
Many application allow users to let users choose FILES_AND_DIRECTORIES. Having two buttons, "Choose directory..." and "Choose files..." as a workaround, is just bad UX when all the current OSes support file-or-folder choosers just fine.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Let users decide what they want to select, rather than limiting them to either files or folders from the get go.