Is there any documentation for the file?

Hi. I found the java code really not easy to understand. Is there anyone who can provide me with some documentations, links, or references of any kind? Many thanks.

Welcome to the GraphHopper forum. Please do not post duplicate topics. Also please be more descriptive and paste code only formatted. Otherwise others will have a hard time to read and understand what you need and this might decrease the chance that you get an answer.