mustang - 2010-02-07

I have finished total begineer  and persistence tutorials. Both were great!!
I have a few questions:
- the uid that is created for the serialized classes to make it work even if there is a change in the class. How this is done in xml? And how do you create a field and declare it as optional or with a default value? is this done in the constructor?
-Regarding the library example, if you wanted to use it in a real life situation, how would you do to represent many units of the same book? and would you persist every time there is a change the hole MyLibrary or could you update just a part of the xml file (I don´t know if this is possible)?

I would be interested in a tutorial of java and databases (sql) , something about swing and threats.

Also, for the next tutorials I think it would be better if the example program were more advanced and finally, the only thing that I would like you to explain a bit more is how you design things, for example when you write the test classes you know what the methods will return and have a clear idea of how they will be, but if I were trying to do something on my own, I would have problems defining the test classes first. I don´t know if what I mean is clear.

Thanks for these great tutorials!!!