The concept for JavaFX seems to be that your JavaFX Application is the control center for everything. But what if you would like to run an application as a new screen and to be able to run multiple applications and the same application multiple times? This turns out to be difficult. I spent most of a day trying to figure out how to do it and I think that I came up with a reasonable solution and so wanted to share.

Here is the main utility class and method. You create an application that you want to display i.e. x = new MyApplication(). Then you just call JavaFXUtil.runApplication(…). This will make sure JavaFX is initialized, start your application and block until it is ready to be accessed externally.

public class JavaFXUtil {
   public static void runApplication(final Application application)
           throws InterruptedException {
      InitializeFXApplication.initializeJavaFX();
      final WaitObject wait = new WaitObject();
      Platform.runLater(
              new Runnable() {
         @Override
         public void run() {
            try {
               application.init();
               Stage stage = new Stage();
               application.start(stage);
               wait.ready();
            } catch (Exception ex) {
               Logger.getLogger(JavaFXUtil.class.getName()).log(Level.SEVERE, null, ex);
            }
         }
      });
      wait.waitUntilReady();
   }
   private JavaFXUtil() {
   }
}

This utility function depends on two other helper classes:

public class InitializeFXApplication extends Application {
   private static boolean started = false;
   private static WaitObject wait = new WaitObject();
   @Override
   public void start(Stage stage) throws Exception {
      started = true;
      wait.ready();
   }
   public static void initializeJavaFX() throws InterruptedException {
      if (started) {
         return;
      }
      new Thread() {
         @Override
         public void run() {
            Application.launch(InitializeFXApplication.class);
         }
      }.start();
      wait.waitUntilReady();
      Logger.getLogger(InitializeFXApplication.class.getName()).log(Level.INFO, "JavaFX initialized");
   }
}

This is the class that makes sure JavaFX environment is initialized.

public class WaitObject {
   private CountDownLatch latch = new CountDownLatch(1);
   public void ready() {
      latch.countDown();
   }
   public void waitUntilReady() throws InterruptedException {
      latch.await();
   }
   public boolean isReady() {
      return latch.getCount() == 0;
   }
}

This is just a helper object to manage waiting for resources to be available.