This is such a key point and yet also quite confusing. Obviously copyright is not patents. Copyright is about preventing literal copying of someone's creation.

So.., if you implement an API in a different programming language, such that the text and structure is different, and yet the function remains the same... then have you not infringed any copyright?

Copyright is about literal reuse of someones functional product, not about reuse of the abstract ideas that make up it.

To me an API, is just a formalization of declaring your intention to implement a particular functionality.

That basically used to be true, but this trial was over the "sequence, structure, and organization" of the API.

How can you copy an API without looking at the original API? They might not have looked the implementation, but if the API itself is copyrighted, won't looking at it suffice to be infringement?

If there is one thing I've learnt for sure from all the random forum posts used in this trial, it is that "IANAL" is a good thing to say!

Nonetheless, I don't think the clean-roomness or otherwise of an implementation has an impact on this. Otherwise someone could copy music by listening to it and replaying it.

Like you said: the copyright is on the text, pattern and structure of the code. But it doesn't matter how it was replicated.

Reverse engineering is not a defense against infringement if the subject of reverse engineering is copyright-protected.

It generally is. That's the whole point of clean-room reimplementation. You have one set of engineers that reverse engineers a product to develop a spec, and another set that implements the same functionality from the spec. That's kosher and has been upheld in several court cases.

The trouble for doing that with Java APIs is the spec basically is the class declarations. You don't just need to "do the same thing" you need a tangible source file that has at least in part the same text.

It kind of depends - in some jurisdictions, for example, interoperability requirements is a sufficient defense against copyright infringement, i.e., if you've built your product so that interoperating with it requires [re]using copyrighted parts, then it's okay to do so (up to the extent required for interoperability) even if you explicitly forbid it.

Sane laws such as that automatically prevent issues such as this Java API dispute and also things such as the attempts to block interoperability for coffee machine "pods" by requiring a copyrighted magic string and using DMCA to prevent others from using it.