Opera Software has ported the mini version of its eponymous browser onto Google's Android platform.
Opera Mini is a Java ME (Micro Edition) application, so Opera Labs ported an open source application called MicroEmulator to Android, which allowed it to run its existing code without modification. MicroEmulator is designed to run Java ME applications on top of Java SE (Standard Edition), and as the Android APIs are based on Java SE it wasn't too complex to get MicroEmulator running on Android.
The most difficult part of the project was apparently dealing with the lack of documentation on the Android APIs, and the fact that there's no Android hardware to work with.
Android devices should be up to running Opera Mobile, the version optimised for smartphones, but that version isn't written in Java so will be a more complex porting task.
The lack of hardware is certainly what's driving Opera to do this work; manufacturers around the world are looking to make Android handsets, and all those handsets are going to need a web browser.
Companies using Symbian or Windows Mobile handsets have obvious default options, but those looking at Android might be more open to pre-installation of Opera. ®