To save defaults from your app for the next time, there is the PropertiesFile class.
It inherits a PropertiesSet, so you can add a property for everything you want to save (it ends up in an XML).
You will have to propagate the value changes yourself, either by overriding the propertyChanged() method, or add a ChangeListener.
I am not sure, there might exist an automatic way to link that as well, and @matkatmusic once posted his own solution for that, if you want to use the forum search.
(here it is: ScopedValueSaver - never worry about App State again)