java.lang.Object | ||
↳ | java.util.prefs.Preferences | |
↳ | java.util.prefs.AbstractPreferences |
This class provides a skeletal implementation of the Preferences
class, greatly easing the task of implementing it.
This class is for Preferences implementers only.
Normal users of the Preferences facility should have no need to
consult this documentation. The Preferences
documentation
should suffice.
Implementors must override the nine abstract service-provider interface
(SPI) methods: getSpi(String)
, putSpi(String, String)
,
removeSpi(String)
, childSpi(String)
, removeNodeSpi()
, keysSpi()
, childrenNamesSpi()
, syncSpi()
and flushSpi()
. All of the concrete methods specify
precisely how they are implemented atop these SPI methods. The implementor
may, at his discretion, override one or more of the concrete methods if the
default implementation is unsatisfactory for any reason, such as
performance.
The SPI methods fall into three groups concerning exception
behavior. The getSpi method should never throw exceptions, but it
doesn't really matter, as any exception thrown by this method will be
intercepted by get(String, String)
, which will return the specified
default value to the caller. The removeNodeSpi, keysSpi,
childrenNamesSpi, syncSpi and flushSpi methods are specified
to throw BackingStoreException
, and the implementation is required
to throw this checked exception if it is unable to perform the operation.
The exception propagates outward, causing the corresponding API method
to fail.
The remaining SPI methods putSpi(String, String)
, removeSpi(String)
and childSpi(String)
have more complicated
exception behavior. They are not specified to throw
BackingStoreException, as they can generally obey their contracts
even if the backing store is unavailable. This is true because they return
no information and their effects are not required to become permanent until
a subsequent call to flush()
or
sync()
. Generally speaking, these SPI methods should not
throw exceptions. In some implementations, there may be circumstances
under which these calls cannot even enqueue the requested operation for
later processing. Even under these circumstances it is generally better to
simply ignore the invocation and return, rather than throwing an
exception. Under these circumstances, however, all subsequent invocations
of flush() and sync should return false, as
returning true would imply that all previous operations had
successfully been made permanent.
There is one circumstance under which putSpi, removeSpi and
childSpi should throw an exception: if the caller lacks
sufficient privileges on the underlying operating system to perform the
requested operation. This will, for instance, occur on most systems
if a non-privileged user attempts to modify system preferences.
(The required privileges will vary from implementation to
implementation. On some implementations, they are the right to modify the
contents of some directory in the file system; on others they are the right
to modify contents of some key in a registry.) Under any of these
circumstances, it would generally be undesirable to let the program
continue executing as if these operations would become permanent at a later
time. While implementations are not required to throw an exception under
these circumstances, they are encouraged to do so. A SecurityException
would be appropriate.
Most of the SPI methods require the implementation to read or write information at a preferences node. The implementor should beware of the fact that another VM may have concurrently deleted this node from the backing store. It is the implementation's responsibility to recreate the node if it has been deleted.
Implementation note: In Sun's default Preferences
implementations, the user's identity is inherited from the underlying
operating system and does not change for the lifetime of the virtual
machine. It is recognized that server-side Preferences
implementations may have the user identity change from request to request,
implicitly passed to Preferences methods via the use of a
static ThreadLocal
instance. Authors of such implementations are
strongly encouraged to determine the user at the time preferences
are accessed (for example by the get(String, String)
or put(String, String)
method) rather than permanently associating a user
with each Preferences instance. The latter behavior conflicts
with normal Preferences usage and would lead to great confusion.
[Expand]
Inherited Constants | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
From class
java.util.prefs.Preferences
|
Fields | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
lock | An object whose monitor is used to lock this node. | ||||||||||
newNode | This field should be true if this node did not exist in the backing store prior to the creation of this object. |
Protected Constructors | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Creates a preference node with the specified parent and the specified
name relative to its parent.
|
Public Methods | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Implements the absolutePath method as per the specification in
absolutePath() . | |||||||||||
Registers the specified listener to receive node change events
for this node.
| |||||||||||
Registers the specified listener to receive preference change
events for this preference node.
| |||||||||||
Implements the children method as per the specification in
childrenNames() . | |||||||||||
Implements the clear method as per the specification in
clear() . | |||||||||||
Implements the exportNode method as per the specification in
exportNode(OutputStream) . | |||||||||||
Implements the exportSubtree method as per the specification in
exportSubtree(OutputStream) . | |||||||||||
Implements the flush method as per the specification in
flush() . | |||||||||||
Implements the get method as per the specification in
get(String, String) . | |||||||||||
Implements the getBoolean method as per the specification in
getBoolean(String, boolean) . | |||||||||||
Implements the getByteArray method as per the specification in
getByteArray(String, byte[]) . | |||||||||||
Implements the getDouble method as per the specification in
getDouble(String, double) . | |||||||||||
Implements the getFloat method as per the specification in
getFloat(String, float) . | |||||||||||
Implements the getInt method as per the specification in
getInt(String, int) . | |||||||||||
Implements the getLong method as per the specification in
getLong(String, long) . | |||||||||||
Implements the isUserNode method as per the specification in
isUserNode() . | |||||||||||
Implements the keys method as per the specification in
keys() . | |||||||||||
Implements the name method as per the specification in
name() . | |||||||||||
Implements the node method as per the specification in
node(String) . | |||||||||||
Implements the nodeExists method as per the specification in
nodeExists(String) . | |||||||||||
Implements the parent method as per the specification in
parent() . | |||||||||||
Implements the put method as per the specification in
put(String, String) . | |||||||||||
Implements the putBoolean method as per the specification in
putBoolean(String, boolean) . | |||||||||||
Implements the putByteArray method as per the specification in
putByteArray(String, byte[]) . | |||||||||||
Implements the putDouble method as per the specification in
putDouble(String, double) . | |||||||||||
Implements the putFloat method as per the specification in
putFloat(String, float) . | |||||||||||
Implements the putInt method as per the specification in
putInt(String, int) . | |||||||||||
Implements the putLong method as per the specification in
putLong(String, long) . | |||||||||||
Implements the remove(String) method as per the specification
in
remove(String) . | |||||||||||
Implements the removeNode() method as per the specification in
removeNode() . | |||||||||||
Removes the specified NodeChangeListener, so it no longer
receives change events.
| |||||||||||
Removes the specified preference change listener, so it no longer
receives preference change events.
| |||||||||||
Implements the sync method as per the specification in
sync() . | |||||||||||
Returns the absolute path name of this preferences node.
|
Protected Methods | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Returns all known unremoved children of this node.
| |||||||||||
Returns the named child of this preference node, creating it if it does
not already exist.
| |||||||||||
Returns the names of the children of this preference node.
| |||||||||||
This method is invoked with this node locked.
| |||||||||||
Returns the named child if it exists, or null if it does not.
| |||||||||||
Return the value associated with the specified key at this preference
node, or null if there is no association for this key, or the
association cannot be determined at this time.
| |||||||||||
Returns true iff this node (or an ancestor) has been
removed with the
removeNode() method. | |||||||||||
Returns all of the keys that have an associated value in this
preference node.
| |||||||||||
Put the given key-value association into this preference node.
| |||||||||||
Removes this preference node, invalidating it and any preferences that
it contains.
| |||||||||||
Remove the association (if any) for the specified key at this
preference node.
| |||||||||||
This method is invoked with this node locked.
|
[Expand]
Inherited Methods | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
From class
java.util.prefs.Preferences
| |||||||||||
From class
java.lang.Object
|
An object whose monitor is used to lock this node. This object is used in preference to the node itself to reduce the likelihood of intentional or unintentional denial of service due to a locked node. To avoid deadlock, a node is never locked by a thread that holds a lock on a descendant of that node.
This field should be true if this node did not exist in the backing store prior to the creation of this object. The field is initialized to false, but may be set to true by a subclass constructor (and should not be modified thereafter). This field indicates whether a node change event should be fired when creation is complete.
Creates a preference node with the specified parent and the specified name relative to its parent.
parent | the parent of this preference node, or null if this is the root. |
---|---|
name | the name of this preference node, relative to its parent, or "" if this is the root. |
IllegalArgumentException | if name contains a slash ('/'), or parent is null and name isn't "". |
---|
Implements the absolutePath method as per the specification in
absolutePath()
.
This implementation merely returns the absolute path name that was computed at the time that this node was constructed (based on the name that was passed to this node's constructor, and the names that were passed to this node's ancestors' constructors).
Registers the specified listener to receive node change events
for this node. A node change event is generated when a child node is
added to or removed from this node. (A single removeNode()
invocation results in multiple node change events, one for every
node in the subtree rooted at the removed node.)
Events are only guaranteed for changes made within the same JVM as the registered listener, though some implementations may generate events for changes made outside this JVM. Events may be generated before the changes have become permanent. Events are not generated when indirect descendants of this node are added or removed; a caller desiring such events must register with each descendant.
Few guarantees can be made regarding node creation. Because nodes are created implicitly upon access, it may not be feasible for an implementation to determine whether a child node existed in the backing store prior to access (for example, because the backing store is unreachable or cached information is out of date). Under these circumstances, implementations are neither required to generate node change events nor prohibited from doing so.
ncl | The NodeChangeListener to add. |
---|
Registers the specified listener to receive preference change
events for this preference node. A preference change event is
generated when a preference is added to this node, removed from this
node, or when the value associated with a preference is changed.
(Preference change events are not generated by the removeNode()
method, which generates a node change event.
Preference change events are generated by the clear
method.)
Events are only guaranteed for changes made within the same JVM as the registered listener, though some implementations may generate events for changes made outside this JVM. Events may be generated before the changes have been made persistent. Events are not generated when preferences are modified in descendants of this node; a caller desiring such events must register with each descendant.
pcl | The preference change listener to add. |
---|
Implements the children method as per the specification in
childrenNames()
.
This implementation obtains this preference node's lock, checks that
the node has not been removed, constructs a TreeSet initialized
to the names of children already cached (the children in this node's
"child-cache"), invokes childrenNamesSpi()
, and adds all of the
returned child-names into the set. The elements of the tree set are
dumped into a String array using the toArray method,
and this array is returned.
BackingStoreException | if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it. |
---|---|
IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method. |
Implements the clear method as per the specification in
clear()
.
This implementation obtains this preference node's lock,
invokes keys()
to obtain an array of keys, and
iterates over the array invoking remove(String)
on each key.
BackingStoreException | if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it. |
---|---|
IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method.
|
Implements the exportNode method as per the specification in
exportNode(OutputStream)
.
os | the output stream on which to emit the XML document. |
---|
IOException | if writing to the specified output stream results in an IOException. |
---|---|
BackingStoreException | if preference data cannot be read from backing store. |
Implements the exportSubtree method as per the specification in
exportSubtree(OutputStream)
.
os | the output stream on which to emit the XML document. |
---|
IOException | if writing to the specified output stream results in an IOException. |
---|---|
BackingStoreException | if preference data cannot be read from backing store. |
Implements the flush method as per the specification in
flush()
.
This implementation calls a recursive helper method that locks this node, invokes flushSpi() on it, unlocks this node, and recursively invokes this method on each "cached child." A cached child is a child of this node that has been created in this VM and not subsequently removed. In effect, this method does a depth first traversal of the "cached subtree" rooted at this node, calling flushSpi() on each node in the subTree while only that node is locked. Note that flushSpi() is invoked top-down.
If this method is invoked on a node that has been removed with
the removeNode()
method, flushSpi() is invoked on this node,
but not on others.
BackingStoreException | if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it. |
---|
Implements the get method as per the specification in
get(String, String)
.
This implementation first checks to see if key is
null throwing a NullPointerException if this is
the case. Then it obtains this preference node's lock,
checks that the node has not been removed, invokes getSpi(String)
, and returns the result, unless the getSpi
invocation returns null or throws an exception, in which case
this invocation returns def.
key | key whose associated value is to be returned. |
---|---|
def | the value to be returned in the event that this preference node has no value associated with key. |
IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method. |
---|---|
NullPointerException | if key is null. (A null default is permitted.) |
Implements the getBoolean method as per the specification in
getBoolean(String, boolean)
.
This implementation invokes get(key,
null)
. If the return value is non-null, it is compared with
"true" using equalsIgnoreCase(String)
. If the
comparison returns true, this invocation returns
true. Otherwise, the original return value is compared with
"false", again using equalsIgnoreCase(String)
.
If the comparison returns true, this invocation returns
false. Otherwise, this invocation returns def.
key | key whose associated value is to be returned as a boolean. |
---|---|
def | the value to be returned in the event that this preference node has no value associated with key or the associated value cannot be interpreted as a boolean. |
IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method. |
---|---|
NullPointerException | if key is null. |
Implements the getByteArray method as per the specification in
getByteArray(String, byte[])
.
key | key whose associated value is to be returned as a byte array. |
---|---|
def | the value to be returned in the event that this preference node has no value associated with key or the associated value cannot be interpreted as a byte array. |
IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method. |
---|---|
NullPointerException | if key is null. (A null value for def is permitted.) |
Implements the getDouble method as per the specification in
getDouble(String, double)
.
This implementation invokes get(key,
null)
. If the return value is non-null, the implementation
attempts to translate it to an double with
parseDouble(String)
. If the attempt succeeds, the return
value is returned by this method. Otherwise, def is returned.
key | key whose associated value is to be returned as a double. |
---|---|
def | the value to be returned in the event that this preference node has no value associated with key or the associated value cannot be interpreted as a double. |
IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method. |
---|---|
NullPointerException | if key is null. |
Implements the getFloat method as per the specification in
getFloat(String, float)
.
This implementation invokes get(key,
null)
. If the return value is non-null, the implementation
attempts to translate it to an float with
parseFloat(String)
. If the attempt succeeds, the return
value is returned by this method. Otherwise, def is returned.
key | key whose associated value is to be returned as a float. |
---|---|
def | the value to be returned in the event that this preference node has no value associated with key or the associated value cannot be interpreted as a float. |
IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method. |
---|---|
NullPointerException | if key is null. |
Implements the getInt method as per the specification in
getInt(String, int)
.
This implementation invokes get(key,
null)
. If the return value is non-null, the implementation
attempts to translate it to an int with
parseInt(String)
. If the attempt succeeds, the return
value is returned by this method. Otherwise, def is returned.
key | key whose associated value is to be returned as an int. |
---|---|
def | the value to be returned in the event that this preference node has no value associated with key or the associated value cannot be interpreted as an int. |
IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method. |
---|---|
NullPointerException | if key is null. |
Implements the getLong method as per the specification in
getLong(String, long)
.
This implementation invokes get(key,
null)
. If the return value is non-null, the implementation
attempts to translate it to a long with
parseLong(String)
. If the attempt succeeds, the return
value is returned by this method. Otherwise, def is returned.
key | key whose associated value is to be returned as a long. |
---|---|
def | the value to be returned in the event that this preference node has no value associated with key or the associated value cannot be interpreted as a long. |
IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method. |
---|---|
NullPointerException | if key is null. |
Implements the isUserNode method as per the specification in
isUserNode()
.
This implementation compares this node's root node (which is stored
in a private field) with the value returned by
userRoot()
. If the two object references are
identical, this method returns true.
Implements the keys method as per the specification in
keys()
.
This implementation obtains this preference node's lock, checks that
the node has not been removed and invokes keysSpi()
.
BackingStoreException | if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it. |
---|---|
IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method.
|
Implements the name method as per the specification in
name()
.
This implementation merely returns the name that was passed to this node's constructor.
Implements the node method as per the specification in
node(String)
.
This implementation obtains this preference node's lock and checks
that the node has not been removed. If path is "",
this node is returned; if path is "/", this node's
root is returned. If the first character in path is
not '/', the implementation breaks path into
tokens and recursively traverses the path from this node to the
named node, "consuming" a name and a slash from path at
each step of the traversal. At each step, the current node is locked
and the node's child-cache is checked for the named node. If it is
not found, the name is checked to make sure its length does not
exceed MAX_NAME_LENGTH. Then the childSpi(String)
method is invoked, and the result stored in this node's child-cache.
If the newly created Preferences object's newNode
field is true and there are any node change listeners,
a notification event is enqueued for processing by the event dispatch
thread.
When there are no more tokens, the last value found in the child-cache or returned by childSpi is returned by this method. If during the traversal, two "/" tokens occur consecutively, or the final token is "/" (rather than a name), an appropriate IllegalArgumentException is thrown.
If the first character of path is '/'
(indicating an absolute path name) this preference node's
lock is dropped prior to breaking path into tokens, and
this method recursively traverses the path starting from the root
(rather than starting from this node). The traversal is otherwise
identical to the one described for relative path names. Dropping
the lock on this node prior to commencing the traversal at the root
node is essential to avoid the possibility of deadlock, as per the
locking invariant
.
path | the path name of the preference node to return. |
---|
IllegalArgumentException | if the path name is invalid (i.e., it contains multiple consecutive slash characters, or ends with a slash character and is more than one character long). |
---|---|
IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method.
|
Implements the nodeExists method as per the specification in
nodeExists(String)
.
This implementation is very similar to node(String)
,
except that getChild(String)
is used instead of childSpi(String)
.
path | the path name of the node whose existence is to be checked. |
---|
BackingStoreException | if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it. |
---|---|
IllegalArgumentException | if the path name is invalid (i.e., it contains multiple consecutive slash characters, or ends with a slash character and is more than one character long). |
IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method and
pathname is not the empty string ("").
|
Implements the parent method as per the specification in
parent()
.
This implementation obtains this preference node's lock, checks that the node has not been removed and returns the parent value that was passed to this node's constructor.
IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method.
|
---|
Implements the put method as per the specification in
put(String, String)
.
This implementation checks that the key and value are legal,
obtains this preference node's lock, checks that the node
has not been removed, invokes putSpi(String, String)
, and if
there are any preference change listeners, enqueues a notification
event for processing by the event dispatch thread.
key | key with which the specified value is to be associated. |
---|---|
value | value to be associated with the specified key. |
NullPointerException | if key or value is null. |
---|---|
IllegalArgumentException | if key.length() exceeds MAX_KEY_LENGTH or if value.length exceeds MAX_VALUE_LENGTH. |
IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method.
|
Implements the putBoolean method as per the specification in
putBoolean(String, boolean)
.
This implementation translates value to a string with
valueOf(boolean)
and invokes put(String, String)
on the result.
key | key with which the string form of value is to be associated. |
---|---|
value | value whose string form is to be associated with key. |
NullPointerException | if key is null. |
---|---|
IllegalArgumentException | if key.length() exceeds MAX_KEY_LENGTH. |
IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method.
|
Implements the putByteArray method as per the specification in
putByteArray(String, byte[])
.
key | key with which the string form of value is to be associated. |
---|---|
value | value whose string form is to be associated with key. |
NullPointerException | if key or value is null. |
---|---|
IllegalArgumentException | if key.length() exceeds MAX_KEY_LENGTH or if value.length exceeds MAX_VALUE_LENGTH*3/4. |
IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method.
|
Implements the putDouble method as per the specification in
putDouble(String, double)
.
This implementation translates value to a string with
toString(double)
and invokes put(String, String)
on the result.
key | key with which the string form of value is to be associated. |
---|---|
value | value whose string form is to be associated with key. |
NullPointerException | if key is null. |
---|---|
IllegalArgumentException | if key.length() exceeds MAX_KEY_LENGTH. |
IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method.
|
Implements the putFloat method as per the specification in
putFloat(String, float)
.
This implementation translates value to a string with
toString(float)
and invokes put(String, String)
on the result.
key | key with which the string form of value is to be associated. |
---|---|
value | value whose string form is to be associated with key. |
NullPointerException | if key is null. |
---|---|
IllegalArgumentException | if key.length() exceeds MAX_KEY_LENGTH. |
IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method.
|
Implements the putInt method as per the specification in
putInt(String, int)
.
This implementation translates value to a string with
toString(int)
and invokes put(String, String)
on the result.
key | key with which the string form of value is to be associated. |
---|---|
value | value whose string form is to be associated with key. |
NullPointerException | if key is null. |
---|---|
IllegalArgumentException | if key.length() exceeds MAX_KEY_LENGTH. |
IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method.
|
Implements the putLong method as per the specification in
putLong(String, long)
.
This implementation translates value to a string with
toString(long)
and invokes put(String, String)
on the result.
key | key with which the string form of value is to be associated. |
---|---|
value | value whose string form is to be associated with key. |
NullPointerException | if key is null. |
---|---|
IllegalArgumentException | if key.length() exceeds MAX_KEY_LENGTH. |
IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method.
|
Implements the remove(String) method as per the specification
in remove(String)
.
This implementation obtains this preference node's lock,
checks that the node has not been removed, invokes
removeSpi(String)
and if there are any preference
change listeners, enqueues a notification event for processing by the
event dispatch thread.
key | key whose mapping is to be removed from the preference node. |
---|
IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method.
|
---|
Implements the removeNode() method as per the specification in
removeNode()
.
This implementation checks to see that this node is the root; if so,
it throws an appropriate exception. Then, it locks this node's parent,
and calls a recursive helper method that traverses the subtree rooted at
this node. The recursive method locks the node on which it was called,
checks that it has not already been removed, and then ensures that all
of its children are cached: The childrenNamesSpi()
method is
invoked and each returned child name is checked for containment in the
child-cache. If a child is not already cached, the childSpi(String)
method is invoked to create a Preferences
instance for it, and this instance is put into the child-cache. Then
the helper method calls itself recursively on each node contained in its
child-cache. Next, it invokes removeNodeSpi()
, marks itself
as removed, and removes itself from its parent's child-cache. Finally,
if there are any node change listeners, it enqueues a notification
event for processing by the event dispatch thread.
Note that the helper method is always invoked with all ancestors up to the "closest non-removed ancestor" locked.
IllegalStateException | if this node (or an ancestor) has already
been removed with the removeNode() method. |
---|---|
UnsupportedOperationException | if this method is invoked on the root node. |
BackingStoreException | if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it. |
Removes the specified NodeChangeListener, so it no longer receives change events.
ncl | The NodeChangeListener to remove. |
---|
Removes the specified preference change listener, so it no longer receives preference change events.
pcl | The preference change listener to remove. |
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Implements the sync method as per the specification in
sync()
.
This implementation calls a recursive helper method that locks this node, invokes syncSpi() on it, unlocks this node, and recursively invokes this method on each "cached child." A cached child is a child of this node that has been created in this VM and not subsequently removed. In effect, this method does a depth first traversal of the "cached subtree" rooted at this node, calling syncSpi() on each node in the subTree while only that node is locked. Note that syncSpi() is invoked top-down.
BackingStoreException | if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it. |
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IllegalStateException | if this node (or an ancestor) has been
removed with the removeNode() method. |
Returns the absolute path name of this preferences node.
Returns all known unremoved children of this node.
Returns the named child of this preference node, creating it if it does
not already exist. It is guaranteed that name is non-null,
non-empty, does not contain the slash character ('/'), and is no longer
than MAX_NAME_LENGTH
characters. Also, it is guaranteed that
this node has not been removed. (The implementor needn't check for any
of these things.)
Finally, it is guaranteed that the named node has not been returned
by a previous invocation of this method or getChild(String)
after the last time that it was removed. In other words, a cached
value will always be used in preference to invoking this method.
Subclasses need not maintain their own cache of previously returned
children.
The implementer must ensure that the returned node has not been removed. If a like-named child of this node was previously removed, the implementer must return a newly constructed AbstractPreferences node; once removed, an AbstractPreferences node cannot be "resuscitated."
If this method causes a node to be created, this node is not guaranteed to be persistent until the flush method is invoked on this node or one of its ancestors (or descendants).
This method is invoked with the lock on this node held.
name | The name of the child node to return, relative to this preference node. |
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Returns the names of the children of this preference node. (The returned array will be of size zero if this node has no children.) This method need not return the names of any nodes already cached, but may do so without harm.
This method is invoked with the lock on this node held.
If this node throws a BackingStoreException, the exception
will propagate out beyond the enclosing childrenNames()
invocation.
BackingStoreException | if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it. |
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This method is invoked with this node locked. The contract of this method is to force any cached changes in the contents of this preference node to the backing store, guaranteeing their persistence. (It is perfectly possible that this node does not exist on the backing store, either because it has been deleted by another VM, or because it has not yet been created.) Note that this method should not flush the preferences in any subnodes of this node. If the backing store naturally flushes an entire subtree at once, the implementer is encouraged to override flush(), rather than merely overriding this method.
If this node throws a BackingStoreException, the exception
will propagate out beyond the enclosing flush()
invocation.
BackingStoreException | if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it. |
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Returns the named child if it exists, or null if it does not.
It is guaranteed that nodeName is non-null, non-empty,
does not contain the slash character ('/'), and is no longer than
MAX_NAME_LENGTH
characters. Also, it is guaranteed
that this node has not been removed. (The implementor needn't check
for any of these things if he chooses to override this method.)
Finally, it is guaranteed that the named node has not been returned
by a previous invocation of this method or childSpi(String)
after the
last time that it was removed. In other words, a cached value will
always be used in preference to invoking this method. (The implementor
needn't maintain his own cache of previously returned children if he
chooses to override this method.)
This implementation obtains this preference node's lock, invokes
childrenNames()
to get an array of the names of this node's
children, and iterates over the array comparing the name of each child
with the specified node name. If a child node has the correct name,
the childSpi(String)
method is invoked and the resulting
node is returned. If the iteration completes without finding the
specified name, null is returned.
nodeName | name of the child to be searched for. |
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BackingStoreException | if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it. |
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Return the value associated with the specified key at this preference node, or null if there is no association for this key, or the association cannot be determined at this time. It is guaranteed that key is non-null. Also, it is guaranteed that this node has not been removed. (The implementor needn't check for either of these things.)
Generally speaking, this method should not throw an exception under any circumstances. If, however, if it does throw an exception, the exception will be intercepted and treated as a null return value.
This method is invoked with the lock on this node held.
Returns true iff this node (or an ancestor) has been
removed with the removeNode()
method. This method
locks this node prior to returning the contents of the private
field used to track this state.
removeNode()
method.
Returns all of the keys that have an associated value in this preference node. (The returned array will be of size zero if this node has no preferences.) It is guaranteed that this node has not been removed.
This method is invoked with the lock on this node held.
If this node throws a BackingStoreException, the exception
will propagate out beyond the enclosing keys()
invocation.
BackingStoreException | if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it. |
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Put the given key-value association into this preference node. It is guaranteed that key and value are non-null and of legal length. Also, it is guaranteed that this node has not been removed. (The implementor needn't check for any of these things.)
This method is invoked with the lock on this node held.
Removes this preference node, invalidating it and any preferences that
it contains. The named child will have no descendants at the time this
invocation is made (i.e., the removeNode()
method
invokes this method repeatedly in a bottom-up fashion, removing each of
a node's descendants before removing the node itself).
This method is invoked with the lock held on this node and its
parent (and all ancestors that are being removed as a
result of a single invocation to removeNode()
).
The removal of a node needn't become persistent until the flush method is invoked on this node (or an ancestor).
If this node throws a BackingStoreException, the exception
will propagate out beyond the enclosing removeNode()
invocation.
BackingStoreException | if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it. |
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Remove the association (if any) for the specified key at this preference node. It is guaranteed that key is non-null. Also, it is guaranteed that this node has not been removed. (The implementor needn't check for either of these things.)
This method is invoked with the lock on this node held.
This method is invoked with this node locked. The contract of this method is to synchronize any cached preferences stored at this node with any stored in the backing store. (It is perfectly possible that this node does not exist on the backing store, either because it has been deleted by another VM, or because it has not yet been created.) Note that this method should not synchronize the preferences in any subnodes of this node. If the backing store naturally syncs an entire subtree at once, the implementer is encouraged to override sync(), rather than merely overriding this method.
If this node throws a BackingStoreException, the exception
will propagate out beyond the enclosing sync()
invocation.
BackingStoreException | if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it. |
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