This is a small game I created in college on top of an open source Java Game Engine - https://github.com/divs1210/3Coffee It helped me understand the basics of Game development, along with multithreading programming in Java.
Instructions: To run the game without compiling, just run "AnasGame.jar". Ensure that the folder "media" is in the same directory as the jar file.
Source Code: Check the folder "src/gameanas"
Disclaimer: 3Coffee is not a professional game engine, and neither is it optimized. And though it is very possible to create production-quality games, a more skilled developer would probably be better off with a nicer engine.