Even if there was a way to easily port an Objective-C application to Java, I wouldn't highly encourage it. iPhone users and Android users are two different families of users. The typical iPhone interface just wouldn't sit well with Android users who aren't familiar with how the iPhone works. Yes, I understand that the UIs of both iPhone and Android seem pretty trivial to learn to most people, but when you break a novice's comfort zone, it puts your applications (or websites) on a higher learning curve.
You should take the time to learn Android's language and UI and develop your application in a fashion that is consistent with how applications on Android work. As said in other answers, if your taught yourself Objective-C, you should find that Java will come pretty easily to you. In addition, in never hurts to know more than one programming language.
