I would have expected patent law to be closer, as patents deal with inventions. If I patented a foot-driven can opener, and you started manufacturing something that worked the same, then I could potentially sue you.

I imagine the reason Oracle are trying their luck under copyright law is that they never applied for a patent for their API (whereas in Berne convention countries, copyright applies to works automatically). Plus in patent law prior art is important, and the design of the Java language (though not much of the API) borrows a lot from C++ and C.