If you want to know better the emulator structure then you can look deeper on this code. Besides provides a great debugger too. After all he uses Java as language as most of you use Java or C you can easily the entire code.
J
The classic chip8 (or schip8) "emulator" project. That one is great because is written in a way easily to read. You can infere some acknowlegde from it. I recommend it if you want to learn about machine code and emulation.