Java APIs

I've been seeing a lot of discussion about covariance and generics around the forums and it seems to me that generics and covariant return types totally separate concepts. It seems to me that covariance and generics can be used to achieve some of the same goals but that they are not inherently tied to each other. Is this a correct assesment? It also seems to me the covaraince would be much easier to add to Java than generics and I can't really think of a reason not to add it. Any comments?