Despite the development of the technology, building a thread-safe UI toolkit is still an enormous challenge due to the complexity of the events and state handling. JavaFX developers decided to follow Swing pattern, and instead of fighting endless deadlocks proclaimed that everything in the UI should be updated from and only from a special thread. It's called JavaFX Application Thread.
For simple programs, you don't notice this requirement, as common JavaFX program entry points are already run on this thread.
Once you started adding multithreading to your application, you will need to take care of the thread you use to update the UI. For example, it's a common approach to run a lengthy operation on the ...
