@groengeel, you do not have to change the target, android operating systems run all apps designed for that version or for any version older than these. For example, I designed this around 2.2, but it will run on my nexus 7, which runs jellybean (4.1/4.2). As for your other question, android coding is quite different from Greenfoot coding. It all runs java, but the methods are different. I am thinking about doing a tutorial to show some of the major differences like you suggested, but there may be a couple other options in the near future (they are mentioned in this discussion: http://www.greenfoot.org/topics/find/4412#post_4412).

@Erdelf, its fine, this is meant to be a learning thing. @paulmartin42, honestly, downloading android and eclipse is complicated, and I think that google does the best job explaining it here: http://developer.android.com/sdk/index.html.

You cannot play a jar on android. It only plays apk files. If you open up the "Balloons" file in the project folder in eclipse, you can create an apk file out of it. However, you need to have downloaded eclipse and the android plugins at this link first: http://developer.android.com/design/downloads/index.html.