Implementation of
PreferencesFactory to return PreferencesExt objects. Using this
method of obtaining a Preferences object is optional; you can also just pass around the
Preferences object explicitly.
The default Preferences.userRoot() and Preferences.systemRoot() are empty. To use
persistent versions, you must set them explicitly through
PreferencesExt.setSystemRoot( PreferencesExt prefs);
PreferencesExt.setUserRoot( PreferencesExt prefs);
and also call:
System.setProperty("java.util.prefs.PreferencesFactory", "ucar.util.prefs.PreferencesExtFactory");