Hi Ayfri, welcome to the forum 
For me your program works in IntelliJ Idea.
Have you added to the project the Processing core libraries (the .jar files)?
In Idea you can add them as Libraries (to the current project) or Global Libraries (if you plan to use them in multiple projects).
Then you need to add them as Dependencies, clicking the + sign and Add Library (to choose libraries added in the previous step above).
Also, you don’t only need the core but a few other files. These are the ones needed in Linux:
Oops not sure why I had pde.jar in that project. Not needed.
What IDE are you using?