FULL PRODUCT VERSION :
java version "1.8.0_74"
Java(TM) SE Runtime Environment (build 1.8.0_74-b02)
Java HotSpot(TM) 64-Bit Server VM (build 25.74-b02, mixed mode)


ADDITIONAL OS VERSION INFORMATION :
 Microsoft Windows [Version 10.0.10586]

EXTRA RELEVANT SYSTEM CONFIGURATION :
MacBook Pro Retina running Boot Camp

A DESCRIPTION OF THE PROBLEM :
Screen.getPrimary().getDpi() returns 0 on MacBook Pro Retina Boot Camp Windows 10.
Happens on 2 tested MacBook Pros. Repeatable every time.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run a JavaFX Application under JVM 8u74 in a MacBook Pro Retina Boot Camp Windows 10 environment.
Call Screen.getPrimary().getDpi().

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The method should return the Retina screen's dots per inch, possibly modified by some scaling factor negotiated between Windows 10 and the JVM.
ACTUAL -
The method returns 0.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import javafx.application.Application;
import javafx.stage.Screen;
import javafx.stage.Stage;

public class DemoBadDpiOnMacRetinaBootCampWindows10 extends Application {

   @Override
   public void start( final Stage primaryStage ) throws Exception {
      System.out.println( "Screen.getPrimary().getDpi(): " + Screen.getPrimary()
                                                                  .getDpi() );
   }

   public static void main( final String[] args ) {
      launch( args );
   }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Check for an unreasonable value, and if so then fall back to AWT Toolkit.getDefaultToolkit().getScreenResolution().