[VBprogrammer]

> Is also a matter of performance (no wonder Java code is that slow)

Surely these would be trivially inlined?

[Someone]

All public non-final methods in Java are virtual, so it is not _that_ trivial. You would have to check all subclasses that might get passed as an argument and check that again whenever new classes are loaded into the JVM.

[wging]

JVMs are quite smart about this sort of thing, and a nonfinal method can still be inlined, even though the JVM has to safely undo that optimization if a class is loaded. I'm not sure where I learned this originally, but Aleksey Shipilev has a post on method dispatch that should explain it. https://shipilev.net/blog/2015/black-magic-method-dispatch/

[_old_dude_]

It's exactly what the JVM does, it's called Class Hierarchy Analysis (CHA). The VM checks if a method is actually overridden or not.

When a new class is loaded, the analysis checks which codes are no longer valid and mark them for deoptimization.