I’ve coded everything in Processing IDE (PDE) version 3.5.4.
So if you click the download icon from my online sketch and transfer those files to the offline PDE it should just run.
Inside “.pde” files all classes we create are nested.
In order to have static methods inside a nested class its class has to be declared static as well.
On the other hand, top-level classes inside “.java” files are naturally static already.