https://www.vice.com/en_us/article/jgqyn7/supreme-court-rules-reimplementing-an-api-is-not-a-crime

The Supreme Court ruled on Monday that Google’s reimplementation of Oracle's Java API in Android was fair use and not a copyright violation. The ruling puts to bed a decade-long legal saga and is a huge win not only for Google but for all software developers, as reimplementing APIs is very common in software development.

APIs, or Application Programming Interfaces, are libraries of code that can be reimplemented to perform various functions. The Supreme Court has now ruled that this practice, already common among programmers, falls under the fair use exception for copyright.