Is there a way to develop classes for Android and BlackBerry ? In this I mean that BlackBerry and Android have different collections.
So I would like to know what is the best way to develop such files (reflection, different files, ...)
Your best bet is to write to a common interface, so that your higher-level code can be consistent, and the parts that will be different, will be abstracted into their own libraries. This way you can write applications that use a common codebase, though most of the work will take place in your libraries, as that is where you connect to the platform.
This way you can try to minimize redundant work, but take advantage of each platform more completely.
If you limit yourself to what each can do then you are shortchanging your users as there are a great deal you will not be able to do, or do well.