US Supreme Court rules for Google over Oracle

Not quite; the court made no decision about whether or not the code in question is copyrightable, merely that fair use would cover the alleged infringements, and thus there's no reason to think about whether or not the code is copyrightable, because either it is, but fair use means no infringement, or it isn't and thus copyright cannot be infringed by Google's actions. Either way round, the result is that Google has obeyed the law.

The fair use test is actually a complex one. It's not a simple question of whether the copying falls into a bucket of allowed conduct. Instead, the court is supposed to consider multiple factors and decide how they balance each other. Those factors include:

• The amount of copying, both absolute and relative to the whole work
• How it's being used, i.e. commercial or non-profit
• Whether the copied work is likely to compete with the original
• Whether the copying is transformative

In this case, the amount of copying is small, both in absolute amount and relative to the total size of the project, it's used commercially, the court determined it's not likely to compete with the original, and the use was considered to be transformative. Based on that, the court decided it was fair use. But they easily could have decided otherwise if they felt it was likely to compete with Java. I'm not sure the decision was correct- I think it really is competing with Java- but deciding on fair use let the court sidestep the question of whether the code was copyrightable at all.