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Changes to Preferences API Since Original JSR

1. Added support for per-system preferences.
    
2. Eliminated forClass method. We we unable to come up with compelling guidelines as to when it is appropriate to use forClass in preference to forPackage, so we opted to eliminate the former.
    
3. Added support for long, float and double and byte array preferences.
    
4. Specified that getBoolean was case-insensitive.
    
5. Restricted maximum size of a preference value to 8K characters. This implicitly restricts byte array values to 6K bytes (because of the nominal RFC 2045 Base64 encoding).
    
6. Changed the name of the method fullName to absolutePath, for improved consistency with File.
    
7. Made it mandatory that once a node has been successfully removed, attempting any operation on the corresponding Preferences object will fail with an IllegalStateOperation, with the exception of the name and absolutePath methods. (These two methods are useful from within a NodeChangeEvent, once the node has been removed.)
    
8. Eliminated use of java.beans.PropertyChangeListener in favor of new class PreferenceChangeListener. Added corresponding event class (PreferenceChangeEvent), and renamed add- and remove- listener methods appropriately.
    
9. Added a type-safe convenience method to each change event returning the "source" as a Preferences Object. For PreferenceChangeEvent, it's getNode. For NodeChangeEvent, it's getParent.
    
10. Replaced NodeChangeEvent's getNodeName method with a getChild method, which returns a Preferences object (rather than a string name).
     
11. Disallowed the empty String ("") as node name for nodes other than the root node. (This was already implicit in the spec but needed to be made explicit.)
     
12. Clarified the circumstances under which the methods in Preferences throw a NullPointerException.
     
13. Clarified that it is possible to use the API even when the backing store is inaccessible.
     
14. Clarified that an implementation is free to persist the results before flush is called.
     
15. Made it mandatory that the refresh method flushes pending updates to prevent uncommitted changes from being lost. The resulting call is essentially, a "sync", so we renamed it.
     
16. Eliminated Preferences's no-args constructor and init method (whose only use was to allow serializable Preferences subclasses).
     
17. Clarified that keys method does return non-overridden stored defaults.
     
18. Eliminated restriction that multiple retrievals of the same node must return Preferences objects that are identical object references.
     
19. Greatly expanded SPI and moved all of its methods to a subclass (AbstractPreferences). Skeletal implementation automatically takes care of locking, generation of IllegalStateException, IllegalArgumentException, and many similar things.
     
20. Moved some implementors' notes from Preferences to AbstractPreferences, and eliminated others.
     
21. Replaced use of IOException with (new) BackingStoreException.
     
22. Changed return values of put(String, String) and remove(String) methods not to give you old value, so that they can be used when the backing store is not available. (This may also improve performance.)
     
23. As a consequence of previous change, modified PreferenceChangeEvent not to provide oldValue. (It's possible to emulate the old behavior if you really want to.)
     
24. Modified keys(), children(), nodeExists(String), removeNode(String), clear() to throw BackingStoreException. For the first four, this is necessary; they cannot, in general, get the specified return value if the repository is unavailable. (For clear(), it is as much a convenience for implementers as anything else.)
     
25. Added spec for toString.
     
26. Added clarification that it is not necessary to do a flush prior to JVM termination.
     
27. Added PreferencesFactory interface to enable support of multiple user preference trees in a single VM.
     
28. Changed package name to java.util.prefs
     
29. Added XML-based import/export facility.
     
30. Wrote "proof-of-concept" implementation (SimplePreferences) based on import/export facility. (Not really an API change.)
     
31. Modified the protocol whereby removeChild is called by removeNode: now it is called for each node in the subtree, in bottom-up order.
     
32. Replaced removeNode(String) with removeNode(). There was no compelling reason to pass in the string, and it was ungainly.
     
33. Renamed children method to childrenNames and changed its behavior to return an array containing the names of this nodes children instead of the nodes themselves. This improves performance.
     
34. Modified AbstractPreferences.childrenSpi to return the names of the children, rather than the children themselves. This pushes the translation work "up the hierarchy" out of the individual preferences implementations and into AbstractPreferences.
     
35. Added a new (Throwable) constructor to BackingStoreException, as it will typically be a "chained exception."
     
36. Modified AbstractPreferences.removeNodeSpi() to throw BackingStoreException, as removeNode throws this exception.
     
37. Removed newNode param from AbstractPreferences constructor. Replaced it with protected field, which subclass constructor is obligated to set if appropriate.
     
38. DTD for exported form: modified root and node to require a map, and modified map to contain entry* instead of entry+. This is cleaner, and results in much cleaner XML support code. Also modified preferences to require a root.
     
39. Change name of node conventionally associated with programs in the unnamed package from "" to "".
     
40. Replaced line number support in InvalidPreferencesFormatException with nested exception ("cause") support.
     
41. Change AbstractPreferences.get implementation so that if getSpi(String) throws an exception, it is caught, and the default is returned from get(String).
     
42. Wrote a discussion on the correct exception behavior of the SPI calls in AbstractPreferences.
     
43. Described locking behavior of AbstractPreferences.isRemoved.
     
44. Modified sync spec to allow call on removed node.
     
45. Added automatic change notification to AbstractPreferences.node(String) implementation description.
     
46. Numerous minor API clarifications.