@tiox... Yes, I believe this is a Java issue (although do you have any proof that it dosen't work? 
) Anyways, try different Java themes (search up "how to make java apps use gtk theme" on Google ) and when you find one that works, use that.
This could also be a Materia issue.
If you're talking about @Med_Medin's post on the other hand, it dosen't run into the same issue - that was the materia theme, but I was using materia-compact as my base, so it's more compact - compare @Philippe's screenshot to mine on my site (of gtk3-widget-factory)