The case has now been sent back to a trial which is meant to determine how much Google should pay for its infringement. In 2016, Oracle said that it was owed US$8.8 billion by Google.
Oracle initiated the appeal in February last year, following a May 2016 verdict that found Google's use of the Java APIs was covered by fair use.
A statement from Oracle general counsel Dorian Daley said: “The Federal Circuit’s opinion upholds fundamental principles of copyright law and makes clear that Google violated the law. This decision protects creators and consumers from the unlawful abuse of their rights.”
A Google statement said: “We are disappointed the court reversed the jury finding that Java is open and free for everyone.
“This type of ruling will make apps and online services more expensive for users. We are considering our options.”
The legal stoush has been going on since 2010 when Oracle sued Google shortly after it purchased Sun Microsystems and became the owner of Java, claiming that the search engine company had violated its copyright and patents.
But an appeal gave Oracle what it wanted: a ruling that APIs can be copyrighted. This ruling has put developers at risk, as they could be sued for using APIs that they could use freely prior to the trial.
In a second trial that ended in May 2016, a jury found that Google's use of 37 Java APIs in its Android mobile operating system was covered under fair use. As expected, Oracle was not happy with the verdict.