about simplicity, while I wouldn't say Java is a complex language, and I might even agree that the language itself is easy, it's also quite verbose, and it doesn't feel as light to use as golang. I would personally mention two things (besides the verbosity of Java):
1) the OOP in Java kinda leads me to start designing around classes, and I feel I need a solid design/plan right from the start, while in golang I feel a bit more like I'm working with a scripting language, but the interfaces and the way the language works makes it quite easy to refactor code and move things as I need it, and in practice I end up with good organization and modular code precisely because it's very easy to move things around. just that frame of mind is a big change (though this is extremely subjective).
2) when I write Java I feel like I need an IDE. yeah, again partly because of the verbosity and boilerplate, but I also feel the environment is more complex. with golang I just write a "package main; func main() { some code }" and then run "go run myprogram.go". that makes the language feel really light and easy to use. I'm not afraid to try to write a demo program and run it even with my eyes closed. with Java I don't feel so much in direct control, and I regularly end up confused about random configurations and things. I don't try to argue that Java is significantly more complex as a language (the typical programming environment is quite different), but it still feels much heavier and complicated than golang.
well, I'll stop here or I'll end up sounding like a fanboy (I wasn't a big fan of many of the golang design choices at the start)