To reproduce, run the following test program in jigsaw mode:

import javafx.application.Application;
import javafx.application.HostServices;
import javafx.application.Platform;
import javafx.stage.Stage;

public class HostServicesTest extends Application {

    @Override public void start(Stage stage) {
        HostServices hs = getHostServices();
        Platform.exit();
    }
}


$ java HostServicesTest
java.lang.ClassNotFoundException: com.sun.deploy.uitoolkit.impl.fx.HostServicesFactory
at jdk.internal.loader.BuiltinClassLoader.loadClass(java.base@9-internal/BuiltinClassLoader.java:366)
at java.lang.ClassLoader.loadClass(java.base@9-internal/ClassLoader.java:419)
at java.lang.Class.forName0(java.base@9-internal/Native Method)
at java.lang.Class.forName(java.base@9-internal/Class.java:378)
at com.sun.javafx.application.HostServicesDelegate.lambda$getInstance$0(javafx.graphics@9-internal/HostServicesDelegate.java:52)
at java.security.AccessController.doPrivileged(java.base@9-internal/Native Method)
at com.sun.javafx.application.HostServicesDelegate.getInstance(javafx.graphics@9-internal/HostServicesDelegate.java:45)
at javafx.application.HostServices.<init>(javafx.graphics@9-internal/HostServices.java:52)
at javafx.application.Application.getHostServices(javafx.graphics@9-internal/Application.java:334)
at HostServicesTest.start(HostServicesTest.java:9)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$9(javafx.graphics@9-internal/LauncherImpl.java:843)
at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$12(javafx.graphics@9-internal/PlatformImpl.java:452)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$10(javafx.graphics@9-internal/PlatformImpl.java:421)
at java.security.AccessController.doPrivileged(java.base@9-internal/Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$11(javafx.graphics@9-internal/PlatformImpl.java:420)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(javafx.graphics@9-internal/InvokeLaterDispatcher.java:96)
at com.sun.glass.ui.gtk.GtkApplication._runLoop(javafx.graphics@9-internal/Native Method)
at com.sun.glass.ui.gtk.GtkApplication.lambda$runLoop$8(javafx.graphics@9-internal/GtkApplication.java:195)
at java.lang.Thread.run(java.base@9-internal/Thread.java:843)