Google used Java source code and copied few of the modules and made their own JVM (Dalvik).
Now Oracle claims that, this is equal to copyright infringement since Java is developed under collaboration of many companies as an open source.
You can use/distribute Java like you want keeping the original license and information as it's, but what Google did is they made another fork of it and named "Dalvik" and as if they invented Java. This ****ed off Oracle and filed lawsuit against Google.
If Google had done that it would be a clear case of copyright infringement and they would have lost the case quickly.
The issue with copyright in this trial is that it's not about copying code (ie. an outright fork) but about APIs.
To put things in perspective, if APIs are finally ruled subject to copyright then Microsoft could sue Wine for it's reimplementation of the Windows libraries, as they are a clear room implementation (the code is completely different from that of Microsoft) but they obviously need to use the same APIs so Windows apps are able to call the Wine libraries' functions and work transparently.
It seems to me that applying copyrights to APIs would be hugely detrimental for the software industry, although on the other hand being an original piece of work the author has (as with any other work) the right to claim rights on it.
Both choices (copyright and no copyrights on APIs) have their tradeoffs.