You can create a contract class, like the Android APIs do, for instance for the Contacts, where you define your content type, content uri, fields and so on:
http://developer.android.com/reference/android/provider/ContactsContract.html
For the implementation, as Effective Java Item #19 suggest, you can create a "normal" class:
public class MyTodoContract {
private MyTodoContract() {}
public static final String CONTENT_TYPE = ContentResolver.CURSOR_DIR_BASE_TYPE + "/todos";
public static final String CONTENT_ITEM_TYPE = ContentResolver.CURSOR_ITEM_BASE_TYPE + "/todo";
}
If you want to provide this class to your clients you should create a Java Library and provide them the jar.