JavaFX pop up using seperate fxml file

Question

I have been scanning the forums and cannot find the solution I need, so apologies if this is a repost.
I have created an application in SceneBuilder, and want to call a pop up (also created separately in scene builder) when a certain button is pressed.
How?

Answer 1

I use something similar to the following because I want to access methods of the sub window's controller :
FXMLLoader loader = new FXMLLoader(getClass().getResource("/com/my/javafx/Stuff.fxml"));
Parent root = (Parent) loader.load();
MyStuffController controller = (MyStuffController) loader.getController();
Scene scene = new Scene(root);
Stage stage = new Stage();
stage.setScene(scene);
stage.setTitle("My Window");
stage.show();
You can also do it like this
FXMLLoader loader = new FXMLLoader(getClass().getResource("/com/my/javafx/Stuff.fxml"));
Parent root = (Parent) fxmlLoader.load();
Scene scene = new Scene(root);
Stage stage = new Stage();
stage.setScene(scene);
stage.setTitle("My Window");
stage.show();
if you want more of a popup feel, you can use other options to style the window and make it unmovable
stage.initModality(Modality.APPLICATION_MODAL);
stage.initStyle(StageStyle.UNDECORATED);