Not entirely correct, its slightly more complicated than that.
Say you write an short story. And you file a copyright for it with the copyright office.
Now, an anthology editor reads your story and wishes to include it in a collection of short stories that he is preparing. It contains, say 20 other short stories as well. This anthology is a "collective work". The anthology editor did not have copyright over the individual stories - he probably only has certain royalty arrangement with each individual author. But the editor can certainly copyright the layout of the anthology. Maybe he put together a brief intro for each story, maybe he ordered them in some artistic fashion based on progression of ideas in the stories etc. This would be a "collective work" copyright. Under a collective work copyright, the editor could sue another editor for producing a substantially duplicate anthology for copyright infringement. But if another magazine published just one of the stories by itself, the editor could not claim copyright infringement.
So in the case of oracle, oracle could have copyright the design of each API individally, and then also copyrighted the entire collection of APIs, thus copyrighting the "collective work" representing the entire language API. But they didn't. They only copyrighted the entire collection as a single work. Thus they (supposedly) cannot claim copyright infrigement when only a small part of it might have been copied by google. (I am not quite certain here).
What oracle is claiming instead - is that they copyrighted Java as a "collective work". which would allow them to claim copyright over the design of the entire API design, rather than just the source code of API implementation. They claim that this design is their creative input. But in this case, then they would also have needed to copyright individual APIs if they wanted to sue for infringement in those individual APIs. Otherwise they could only sue if someone someone copied the entire (or a very substantial part of) the design. They did not copyright those individual pieces.
Back to the analogy:
According to groklaw, Oracle actually copyrighted the entire anthology as an original single work. Oracle claims it copyrighted the anthology as a "collective work" - this is under question. Also, if it DID actually copyright the anthology as a collective work, it seems they did not file copyrights for the individual stories. As a collective work, thus, they can sue for infringement if another anthology is published with substantially the same layout, copying the creativity that went into putting the anthology together. But, if someone copied just one of the stories, they might not be able to sue for infringement as that would not duplicate the creative work of the anthology itself.
On the other hand, if they claim to have copyright the entire anthology as a single work, then if someone copies just the titles of each story and publishes another anthology with different content but same titles for each story, it might not count as infringement.
At least thats my understanding.