Compiling FX with a recent build of JDK 9 gives the following error:

$ java -version
java version "9-ea"
Java(TM) SE Runtime Environment (build 9-ea+105-2016-02-10-235300.javare.4433)
Java HotSpot(TM) Client VM (build 9-ea+105-2016-02-10-235300.javare.4433, mixed mode)

$ gradle
...
/localhome/kcr/javafx/9-kcr/jfx/rt/modules/swing/src/main/java/javafx/embed/swing/JFXPanel.java:692: error: cannot find symbol
                newScaleFactor = ((SunGraphics2D)g).surfaceData.getDefaultScale();
                                                               ^
  symbol: method getDefaultScale()
  location: variable surfaceData of type SurfaceData

This is a result of changes to the sun.java2d.SurfaceData class for Windows Hi-DPI support -- see JDK-8073320. This class used to have a getDefaultScale() method and now has separate getDefaultScaleX() and getDefaultScaleY() methods.