JavaFX : When/Where are elements/controls instantiated?

Question

All right, I have my first JFX App Up & Running.

Now, I am asking myself how everything is nicely wrapped-up behind the scene. How is all this bunch of FXML transformed into java code with proper instantiation and all ? How does it work ?

I'd Google that if I knew what to write but so far I find a lot about how to use it but not much about how it is made.

Answer 1

The magic happens inside the FXMLLoader .

It receives an FXML file, and parses it with an XML parser. You are forced to use a well-defined set of XML nodes, and the loader knows how to "transform" every type of these XML nodes to the corresponding java object (to a JavaFX Node ) at runtime. If the format of the XML file is not correct (does not fit the defined structure) you will get an exception. This way your nodes are created, one thing left: populate the controller.

To populate the controller, it will use reflection to create an instance of the specified controller class and to set its data members. It iterates through the @FXML annoted fields inside and then set each of them to one of the created objects with the matching fx:id attribute.

In the end by default the public initialize method is called on the controller instance.