How to visit code to get variable, class, and parameter

I am wanting to make a plugin that'll visit over on a class and check for a few things, for example:

I wanted to get the val name "test", the number "5" and the string "Hello", I couldn't find anywhere on how work with a visitor on the documentations.

I found an example which is for a `HighlightVisitor` which I kinda made it work correctly, however had to use Regex and some other methods to get the data I wanted, so I am assuming it's not the best way to do it.

What would be the best way to achieve this? Could someone show me an example?

Thank you!