J2ObjC is an open-source command-line tool from Google that translates Java code to Objective-C for the iOS (iPhone/iPad) platform. This tool enables Java code to be part of an iOS application's build, as no editing of the generated files is necessary. The goal is to write an app's non-UI code (such as data access, or application logic) in Java, which is then shared by web apps (using GWT), Android apps, and iOS app
J2ObjC supports most Java language and runtime features required by client-side application developers, including exceptions, inner and anonymous classes, generic types, threads and reflection. JUnit test translation and execution is also supported
The project homepage is here, and along with Google's Web Toolkit, seems to be under an acceptable FOSS license
It does not strive to be a full replacement for all things Java, and as it notes:
when new projects first start working with it, they usually find new bugs to be fixed. Apparently every Java developer has a slightly different way of using Java, and the tool hasn't translated all possible paths yet
Long time readers of this blog will recall that I have been a critic of Java in FOSS projects particularly in the LSB standards context, and as I predicted, the Oracle anti-FOSS Java lawsuit [against Google it turns out, because they are a juicy target] was filed a couple years later. People working for nasty corporate masters earn their futures
This is not to say that translation layers are without warts and flaws, but at least this provides a partial roadway away from a Java dependency into a code generator that may emit freely licensable code. I'll be tracking this with interest. I have a sample conversion in mind ...