Mobile phone companies used to license Java from Oracle. Instead, they all now use Android instead, a ripped off implementation of Java. Oracle claims they had intentions of moving further into the smartphone space (most mobile Java implementations a decade ago were on dumbphones, AFAIK), but Android shot their plans and the value of their purchase of Java to heck.
In short, Oracle has claimed they bought Java from Sun to make a mobile OS that would've been licensed to manufacturers, and by stealing the Java API from them, devalued that purchase by launching Android for free.
Having coded for Android and JavaME, I can say that JavaME would have never worked right in the smartphone space. It's whole process lifetime architecture is wrong for smartphones. It basically only works with one app running that gets killed on quit otherwise you kill your battery as if your phone doesn't go to sleep.
In fact, the law is intended to protect your business from competition, when that competition is repackaging and reselling your original work. That's the entire point of intellectual property law.
Prior to all of this, for practically a decade, open source projects had been reimplementing parts of Java. For example, I used Java for coding on the original Palm Pilot via Ghost (http://www.cs.utah.edu/~mcdirmid/ghost/) and SuperWaba projects. (https://en.wikipedia.org/wiki/SuperWaba) No one had any problem with this activity prior to Oracle, not even Sun, it was pretty much established a long history that this was acceptable behavior, Sun even encouraged it to some extent, as long as you didn't call the result Java(TM).
Mobile and embedded environments can't run the full Java, and Sun's attempts at this (Embedded Java, Personal Java, MIDP/Jave ME) were awful. Oracle's claims that they were going to make a competitive mobile OS are dubious at best. I joined Oracle's Mobile division in 2001 until 2006, and at the point I left, my impression was that they were more or less wrapping it up, and merged the OracleMobile division back into Oracle Collaboration Suite to work on Enterprise apps like Calendar and Mail.
It is much more likely, given Oracle's history, and the public statements of James Gosling, that Oracle was more or less interested in purchasing Sun's customer base/rolodex, and patent portfolio to shakedown. They had no interest in Sun Labs, Solaris, UltraSPARC T1/Rock/MAGC, or making products out of any of cool tech Sun had developed. Sun had a lot of customers who would buy expensive Solaris boxes, who would be prime customers for databases and ERP software.
The computer industry got its start in spite of copyright, not because of it. Homebrew hackers cloned commercial systems. PC clone makers cloned IBM's BIOS. Intel clone makers clean room cloned x86 chips. Piracy was rampant, and it was the primary way other engineers learned. In the early days of the Web, the very nature of "View Source" allowed everyone to copy everyone else's Website, their markup techniques, their CSS, their Javascript. Again, it is how people learned, how the ecosystem evolved.
Look at what you're doing, someone who has claimed support for OSS in the past, you're supporting the argument that a corporation (Oracle), known for taking a buzz saw to acquisitions to get their customer base Gorden Gecko style, who ships mostly badly engineered software, poor poor Oracle, had their plans for a licensing shakedown, foiled by someone creating a viable smartphone OS that has enabled literally thousands of OEMs to build a vast ecosystem of devices for free.
Would you say the same thing about the developers of WINE if it actually started making an impact in Windows value? What if Google held a copyright over some Web APIs (perhaps Widevine video DRM stuff) that every website used, and they sued Mozilla over a cleanroom implementation that devalued the acquisition, would you be against Mozilla?
I'm literally shocked by anyone taking the position that clean-room API reimplementations deserve copy protection, especially people who claim to support OSS, and anyone defending the rights of $100 billion market cap companies to own API copyrights. This isn't some small time 3rd party library developer being deprived of living expenses. The ability for clean-room reimplementations to happen is how we break monopolies, its how network path-dependencies get disrupted by providing inter-rim migration paths. It's the entire history of the computer industry. It's how Coherent cloned Unix.
GNU and Linux largely cloned AT&T's existing Unix suite of tools in user space. These are essentially APIs, and their organization and collection, certainly represents a creative endeavor. If we were to accept this defense of Oracle, we would be forced to conclude that Unix was massively devalued as well.
The fact that competition that executes better on your idea than you do can devalue your product should not be a defense to have government and courts intervene on your behalf.
As a supporter of open source software, I wholly support Oracle's fight to catch Google trying to evade the GPL. I'm not sure how an open source supporter could really be supportive of your employer lifting from the paid version of a product to avoid having to comply with the GPL. Google's actions here pose a massive threat to anyone who has developed open source software funded by a commercial licensing option.
What I find dubious is not that Oracle might try to make a mobile OS (your argument against this is the subjective opinion that it was "awful"), but Google's claims that their use of the Java API was "fair use". Building a non-interoperable competitor for commercial licensing based on their work doesn't come anywhere near the terms of fair use. By Google's own admission, the choice to do this was an attempt to leech off of developer familiarity with Java rather than any sort of compatibility need.
Open Source -- as in Source Code. GPL protects source. The stuff you actually fork when you type 'git clone'. You really think Richard Stallman would be opposed to someone cleanroom re-implementing a GNU GPL'ed software from scratch that has a compatible API? Stallman called Android a major step forward, and if anything, his problems had nothing to do with subsetting Oracle's API, but issues surrounding Tivoization and binary blobs.
java.io, java.util, java.lang are re-mixes of every other OO runtime going back to smalltalk. I'm not buying this idea that reimplementing List, Map, Set, InputStream, et al, without copying source needs protection.
Moreover, the fact that oodles of subsets of the Java APIs existed for a decade, and Sun never once took any of them to court, buttresses the argument that the CREATORS of the API were not interested in protecting against reimplementation. Even GNU Classpath wasn't a proper fully compatible version of the Java APIs, it could not pass the TCKs, but Sun did not threaten it.
Yes, Google likely chose Java because hundreds of thousands of developers already spoke it. Just like Objective-C choose C and Smalltalk, because so many people already spoke it. What's wrong with building a system that will have a low learning curve and easy to transition to if it is very similar to what people already know? C# was created by Microsoft to resemble Java for similar reasons.
In short, Oracle has claimed they bought Java from Sun to make a mobile OS that would've been licensed to manufacturers, and by stealing the Java API from them, devalued that purchase by launching Android for free.