To compile this program you need JDK17. Moreover, you'll have to add the Processing libraries as a module. To do this, add core.jar from your Processing repertory in the project dependencies.
Since we are using the Processing API, the Game class had to placed be inside a package, so we could give Processing access to it in the module-info file. It can be found in the tetris_game package.
To execute properly the code, you need to compile and launch Game.java from the parent directory of src and resources.
You will find in Documentation.pdf the more precise explanation of the program.