(Some changes in Python 3 I can recall: bytes/str/unicode being the biggest one; fixing mutable variables in nested functions; changing some obscure behavior in class hierarchies and overload resolution; changing things like range() and map() to lazy evaluation.)
For better or for worse, Java has maintained very good (not perfect) compatibility throughout, even with painful changes like generics in 1.5, lambdas in 8, modules in 9, eventual removal of applets and SecurityManager, etc. This also contrasts with C#/.NET, which I think had some breaking changes over the decades.