J2ObjC is an open-source command-line tool from Google that can help with the translation of Java to Objective-C.

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 apps.