The XML is used for configuration and for the view. The first thing you will need to do is read look at the Android Developer's Network to see what is what:
http://developer.android.com/index.html. It has tutorials, design principals, guides, and the all important API.
Next is to make sure your View is separate from your application logic. Android doesn't use Swing or AWT, so you will be re-building your GUI. This is a lot easier if you have a good separation of view from other parts of the application.
Next is to analyze your application for other bits which may need swapping out. Look at the Android API and compare it to the Java API your application actually uses. Not all of the core Java libraries are available, so double check that the classes you use will be available. Similarly examine the third party libraries your application uses and check them for Android compatibility. If you find anything that isn't Android compatible you will need to look up alternatives.
Finally, examine how your application interacts with resources - does it use the file system, does it use a database, the internet, etc... You will probably need to modify these resource-connections to Android compatible alternatives.
It is really hard to take your full application and plop it on Android and get it to work. Often you need to modularize it so you have little independent pieces that you can hook together. You make each module a different library project, and then you make an Android application project which takes the modules that are android compatible and writes android versions of modules which aren't. Similarly, you make a desktop application which takes the modules from the library it can use and builds desktop versions of the other modules to make it work on desktop. Hopefully, the core of your application can be in the modules in the library, and things like database interaction, file system interaction, and GUI are what is left for the platform dependent projects to implement.
