In this context, I am very happy to see Google release the free tool J2ObjC: This library is targeted to translate Java Business Logic code (not UI code!!!) from the Java Source Code into Objective-C source code. The objective of this project really appears to be to share libraries between Java and iOS applications rather than translating entire applications (with UI) from Java into Objective-C: a limitation I think is a great strength!
I hope that soon we will be able to write Business Logic-level code just once and then embed it everywhere!!!