In Eclipse exist a debugger which do the trace and show variables values but this mechanism need also to be learned before to be used.
Well, an other life.
Remain 7 from 9 (if I'm a cat and I don't know).
Until this year I have a lot of inspiration from some sites with java code samples but it became unavailable.https://www.java2s.com or https://www.java3d.org/tutorial.html