It is about having 2 versions: in Java with Processing and in Javascript with P5js.
The idea of this project is, on the one hand, to be able to create small 2D games by being able to understand and access the engine code without needing to understand C++ and on the other hand, especially for the JAVA version, to be able to use libraries to which game engines do not generally have access (such as to do FTP for example) and to use it in applications by completely mastering its graphical interface.
Everything is done using the Processing editor, which is much more accessible than the programs used by professionals.
The use of relatively advanced programming concepts, such as many design patterns, can also be educational for many people (it seems to me) who might find it useful to study its code.