Complex application can’t be built in a single .fxml file. Splitting application across different files help in building easy in maintenance software. Scene Builder support using multi .fxml files and it is really simple in use. If you have not used Scene Builder yet, don’t worry. You can download it from this website. It is powerful and easy to use software to build UI in JavaFX.
At the beginning create a project like an article from the link: JavaFX+Maven+Spring – Step by step
I use Maven project with Spring Boot framework because it makes programming faster and simpler. If you don’t want to use any of them, you don’t have to. The article is the most about using Scene Builder. The difference is that if you’re going to use Java 11 or higher, you have to import JavaFX library manually (here it is done by Maven’s dependencies).
Let’s see the video: