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java.util.prefs
Class Preferences
java.lang.Object
java.util.prefs.Preferences
-
Direct Known Subclasses:
-
AbstractPreferences
-
public abstract class Preferences
- extends Object
A node in a hierarchical collection of preference data. This class allows applications to store and retrieve user and system preference and configuration data. This data is stored persistently in an implementation-dependent backing store. Typical implementations include flat files, OS-specific registries, directory servers and SQL databases. The user of this class needn't be concerned with details of the backing store.
There are two separate trees of preference nodes, one for user preferences and one for system preferences. Each user has a separate user preference tree, and all users in a given system share the same system preference tree. The precise description of "user" and "system" will vary from implementation to implementation. Typical information stored in the user preference tree might include font choice, color choice, or preferred window location and size for a particular application. Typical information stored in the system preference tree might include installation configuration data for an application.
Nodes in a preference tree are named in a similar fashion to directories in a hierarchical file system. Every node in a preference tree has a
node name
(which is not necessarily unique), a unique
absolute path name
, and a path name
relative
to each ancestor including itself.
The root node has a node name of the empty string (""). Every other node has an arbitrary node name, specified at the time it is created. The only restrictions on this name are that it cannot be the empty string, and it cannot contain the slash character ('/').
The root node has an absolute path name of
"/"
. Children of the root node have absolute path names of
"/" +
<node name>
. All other nodes have absolute path names of
<parent's absolute path name>
+ "/" +
<node name>
. Note that all absolute path names begin with the slash character.
A node
n
's path name relative to its ancestor
a
is simply the string that must be appended to
a
's absolute path name in order to form
n
's absolute path name, with the initial slash character (if present) removed. Note that:
-
No relative path names begin with the slash character.
-
Every node's path name relative to itself is the empty string.
-
Every node's path name relative to its parent is its node name (except for the root node, which does not have a parent).
-
Every node's path name relative to the root is its absolute path name with the initial slash character removed.
Note finally that:
-
No path name contains multiple consecutive slash characters.
-
No path name with the exception of the root's absolute path name ends in the slash character.
-
Any string that conforms to these two rules is a valid path name.
All of the methods that modify preferences data are permitted to operate asynchronously; they may return immediately, and changes will eventually propagate to the persistent backing store with an implementation-dependent delay. The
flush
method may be used to synchronously force updates to the backing store. Normal termination of the Java Virtual Machine will
not
result in the loss of pending updates -- an explicit
flush
invocation is
not
required upon termination to ensure that pending updates are made persistent.
All of the methods that read preferences from a
Preferences
object require the invoker to provide a default value. The default value is returned if no value has been previously set
or if the backing store is unavailable
. The intent is to allow applications to operate, albeit with slightly degraded functionality, even if the backing store becomes unavailable. Several methods, like
flush
, have semantics that prevent them from operating if the backing store is unavailable. Ordinary applications should have no need to invoke any of these methods, which can be identified by the fact that they are declared to throw
BackingStoreException
.
The methods in this class may be invoked concurrently by multiple threads in a single JVM without the need for external synchronization, and the results will be equivalent to some serial execution. If this class is used concurrently
by multiple JVMs
that store their preference data in the same backing store, the data store will not be corrupted, but no other guarantees are made concerning the consistency of the preference data.
This class contains an export/import facility, allowing preferences to be "exported" to an XML document, and XML documents representing preferences to be "imported" back into the system. This facility may be used to back up all or part of a preference tree, and subsequently restore from the backup.
The XML document has the following DOCTYPE declaration:
<!DOCTYPE preferences SYSTEM "http://java.sun.com/dtd/preferences.dtd">
Note that the system URI (http://java.sun.com/dtd/preferences.dtd) is
not
accessed when exporting or importing preferences; it merely serves as a string to uniquely identify the DTD, which is:
<?xml version="1.0" encoding="UTF-8"?>
<!-- DTD for a Preferences tree. -->
<!-- The preferences element is at the root of an XML document
representing a Preferences tree. -->
<!ELEMENT preferences (root)>
<!-- The preferences element contains an optional version attribute,
which specifies version of DTD. -->
<!ATTLIST preferences EXTERNAL_XML_VERSION CDATA "0.0" >
<!-- The root element has a map representing the root's preferences
(if any), and one node for each child of the root (if any). -->
<!ELEMENT root (map, node*) >
<!-- Additionally, the root contains a type attribute, which
specifies whether it's the system or user root. -->
<!ATTLIST root
type (system|user) #REQUIRED >
<!-- Each node has a map representing its preferences (if any),
and one node for each child (if any). -->
<!ELEMENT node (map, node*) >
<!-- Additionally, each node has a name attribute -->
<!ATTLIST node
name CDATA #REQUIRED >
<!-- A map represents the preferences stored at a node (if any). -->
<!ELEMENT map (entry*) >
<!-- An entry represents a single preference, which is simply
a key-value pair. -->
<!ELEMENT entry EMPTY >
<!ATTLIST entry
key CDATA #REQUIRED
value CDATA #REQUIRED >
Every
Preferences
implementation must have an associated
PreferencesFactory
implementation. Every J2SE implementation must provide some means of specifying which
PreferencesFactory
implementation is used to generate the root preferences nodes. This allows the administrator to replace the default preferences implementation with an alternative implementation.
Implementation note: In Sun's JRE, the
PreferencesFactory
implementation is located as follows:
-
If the system property
java.util.prefs.PreferencesFactory
is defined, then it is taken to be the fully-qualified name of a class implementing the
PreferencesFactory
interface. The class is loaded and instantiated; if this process fails then an unspecified error is thrown.
-
If a
PreferencesFactory
implementation class file has been installed in a jar file that is visible to the
system class loader
, and that jar file contains a provider-configuration file named
java.util.prefs.PreferencesFactory
in the resource directory
META-INF/services
, then the first class name specified in that file is taken. If more than one such jar file is provided, the first one found will be used. The class is loaded and instantiated; if this process fails then an unspecified error is thrown.
-
Finally, if neither the above-mentioned system property nor an extension jar file is provided, then the system-wide default
PreferencesFactory
implementation for the underlying platform is loaded and instantiated.
-
Since:
-
1.4
Field Summary
|
static int |
MAX_KEY_LENGTH
Maximum length of string allowed as a key (80 characters). |
static int |
MAX_NAME_LENGTH
Maximum length of a node name (80 characters). |
static int |
MAX_VALUE_LENGTH
Maximum length of string allowed as a value (8192 characters). |
Constructor Summary
|
protected |
Preferences
()
Sole constructor. |
Method Summary
|
abstract
String
|
absolutePath
()
Returns this preference node's absolute path name. |
abstract void |
addNodeChangeListener
(
NodeChangeListener
ncl)
Registers the specified listener to receive
node change events
for this node. |
abstract void |
addPreferenceChangeListener
(
PreferenceChangeListener
pcl)
Registers the specified listener to receive
preference change events
for this preference node. |
abstract
String
[] |
childrenNames
()
Returns the names of the children of this preference node, relative to this node. |
abstract void |
clear
()
Removes all of the preferences (key-value associations) in this preference node. |
abstract void |
exportNode
(
OutputStream
os)
Emits on the specified output stream an XML document representing all of the preferences contained in this node (but not its descendants). |
abstract void |
exportSubtree
(
OutputStream
os)
Emits an XML document representing all of the preferences contained in this node and all of its descendants. |
abstract void |
flush
()
Forces any changes in the contents of this preference node and its descendants to the persistent store. |
abstract
String
|
get
(
String
key,
String
def)
Returns the value associated with the specified key in this preference node. |
abstract boolean |
getBoolean
(
String
key, boolean def)
Returns the boolean value represented by the string associated with the specified key in this preference node. |
abstract byte[] |
getByteArray
(
String
key, byte[] def)
Returns the byte array value represented by the string associated with the specified key in this preference node. |
abstract double |
getDouble
(
String
key, double def)
Returns the double value represented by the string associated with the specified key in this preference node. |
abstract float |
getFloat
(
String
key, float def)
Returns the float value represented by the string associated with the specified key in this preference node. |
abstract int |
getInt
(
String
key, int def)
Returns the int value represented by the string associated with the specified key in this preference node. |
abstract long |
getLong
(
String
key, long def)
Returns the long value represented by the string associated with the specified key in this preference node. |
static void |
importPreferences
(
InputStream
is)
Imports all of the preferences represented by the XML document on the specified input stream. |
abstract boolean |
isUserNode
()
Returns
true
if this preference node is in the user preference tree,
false
if it's in the system preference tree. |
abstract
String
[] |
keys
()
Returns all of the keys that have an associated value in this preference node. |
abstract
String
|
name
()
Returns this preference node's name, relative to its parent. |
abstract
Preferences
|
node
(
String
pathName)
Returns the named preference node in the same tree as this node, creating it and any of its ancestors if they do not already exist. |
abstract boolean |
nodeExists
(
String
pathName)
Returns true if the named preference node exists in the same tree as this node. |
abstract
Preferences
|
parent
()
Returns the parent of this preference node, or
null
if this is the root. |
abstract void |
put
(
String
key,
String
value)
Associates the specified value with the specified key in this preference node. |
abstract void |
putBoolean
(
String
key, boolean value)
Associates a string representing the specified boolean value with the specified key in this preference node. |
abstract void |
putByteArray
(
String
key, byte[] value)
Associates a string representing the specified byte array with the specified key in this preference node. |
abstract void |
putDouble
(
String
key, double value)
Associates a string representing the specified double value with the specified key in this preference node. |
abstract void |
putFloat
(
String
key, float value)
Associates a string representing the specified float value with the specified key in this preference node. |
abstract void |
putInt
(
String
key, int value)
Associates a string representing the specified int value with the specified key in this preference node. |
abstract void |
putLong
(
String
key, long value)
Associates a string representing the specified long value with the specified key in this preference node. |
abstract void |
remove
(
String
key)
Removes the value associated with the specified key in this preference node, if any. |
abstract void |
removeNode
()
Removes this preference node and all of its descendants, invalidating any preferences contained in the removed nodes. |
abstract void |
removeNodeChangeListener
(
NodeChangeListener
ncl)
Removes the specified
NodeChangeListener
, so it no longer receives change events. |
abstract void |
removePreferenceChangeListener
(
PreferenceChangeListener
pcl)
Removes the specified preference change listener, so it no longer receives preference change events. |
abstract void |
sync
()
Ensures that future reads from this preference node and its descendants reflect any changes that were committed to the persistent store (from any VM) prior to the
sync
invocation. |
static
Preferences
|
systemNodeForPackage
(
Class
<?> c)
Returns the preference node from the system preference tree that is associated (by convention) with the specified class's package. |
static
Preferences
|
systemRoot
()
Returns the root preference node for the system. |
abstract
String
|
toString
()
Returns a string representation of this preferences node, as if computed by the expression:
(this.isUserNode() ? "User" : "System") + " Preference Node: " + this.absolutePath()
. |
static
Preferences
|
userNodeForPackage
(
Class
<?> c)
Returns the preference node from the calling user's preference tree that is associated (by convention) with the specified class's package. |
static
Preferences
|
userRoot
()
Returns the root preference node for the calling user. |
MAX_KEY_LENGTH
public static final int MAX_KEY_LENGTH
-
Maximum length of string allowed as a key (80 characters).
-
See Also:
-
Constant Field Values
MAX_VALUE_LENGTH
public static final int MAX_VALUE_LENGTH
-
Maximum length of string allowed as a value (8192 characters).
-
See Also:
-
Constant Field Values
MAX_NAME_LENGTH
public static final int MAX_NAME_LENGTH
-
Maximum length of a node name (80 characters).
-
See Also:
-
Constant Field Values
Preferences
protected Preferences()
-
Sole constructor. (For invocation by subclass constructors, typically implicit.)
userNodeForPackage
public static Preferences userNodeForPackage(Class<?> c)
-
Returns the preference node from the calling user's preference tree that is associated (by convention) with the specified class's package. The convention is as follows: the absolute path name of the node is the fully qualified package name, preceded by a slash (
'/'
), and with each period (
'.'
) replaced by a slash. For example the absolute path name of the node associated with the class
com.acme.widget.Foo
com.acme.widget
is
/com/acme/widget
.
This convention does not apply to the unnamed package, whose associated preference node is
<unnamed>
. This node is not intended for long term use, but for convenience in the early development of programs that do not yet belong to a package, and for "throwaway" programs.
Valuable data should not be stored at this node as it is shared by all programs that use it.
A class
Foo
wishing to access preferences pertaining to its package can obtain a preference node as follows:
static Preferences prefs = Preferences.userNodeForPackage(Foo.class);
This idiom obviates the need for using a string to describe the preferences node and decreases the likelihood of a run-time failure. (If the class name is misspelled, it will typically result in a compile-time error.)
Invoking this method will result in the creation of the returned node and its ancestors if they do not already exist. If the returned node did not exist prior to this call, this node and any ancestors that were created by this call are not guaranteed to become permanent until the
flush
method is called on the returned node (or one of its ancestors or descendants).
-
-
Parameters:
-
c - the class for whose package a user preference node is desired.
-
Returns:
-
the user preference node associated with the package of which
c
is a member.
-
Throws:
-
NullPointerException
- if
c
is
null
.
-
SecurityException
- if a security manager is present and it denies
RuntimePermission("preferences")
.
-
See Also:
-
RuntimePermission
systemNodeForPackage
public static Preferences systemNodeForPackage(Class<?> c)
-
Returns the preference node from the system preference tree that is associated (by convention) with the specified class's package. The convention is as follows: the absolute path name of the node is the fully qualified package name, preceded by a slash (
'/'
), and with each period (
'.'
) replaced by a slash. For example the absolute path name of the node associated with the class
com.acme.widget.Foo
com.acme.widget
is
/com/acme/widget
.
This convention does not apply to the unnamed package, whose associated preference node is
<unnamed>
. This node is not intended for long term use, but for convenience in the early development of programs that do not yet belong to a package, and for "throwaway" programs.
Valuable data should not be stored at this node as it is shared by all programs that use it.
A class
Foo
wishing to access preferences pertaining to its package can obtain a preference node as follows:
static Preferences prefs = Preferences.systemNodeForPackage(Foo.class);
This idiom obviates the need for using a string to describe the preferences node and decreases the likelihood of a run-time failure. (If the class name is misspelled, it will typically result in a compile-time error.)
Invoking this method will result in the creation of the returned node and its ancestors if they do not already exist. If the returned node did not exist prior to this call, this node and any ancestors that were created by this call are not guaranteed to become permanent until the
flush
method is called on the returned node (or one of its ancestors or descendants).
-
-
Parameters:
-
c - the class for whose package a system preference node is desired.
-
Returns:
-
the system preference node associated with the package of which
c
is a member.
-
Throws:
-
NullPointerException
- if
c
is
null
.
-
SecurityException
- if a security manager is present and it denies
RuntimePermission("preferences")
.
-
See Also:
-
RuntimePermission
userRoot
public static Preferences userRoot()
-
Returns the root preference node for the calling user.
-
-
Returns:
-
the root preference node for the calling user.
-
Throws:
-
SecurityException
- If a security manager is present and it denies
RuntimePermission("preferences")
.
-
See Also:
-
RuntimePermission
systemRoot
public static Preferences systemRoot()
-
Returns the root preference node for the system.
-
-
Returns:
-
the root preference node for the system.
-
Throws:
-
SecurityException
- If a security manager is present and it denies
RuntimePermission("preferences")
.
-
See Also:
-
RuntimePermission
put
public abstract void put(String key,
String value)
-
Associates the specified value with the specified key in this preference node.
-
-
Parameters:
-
key - key with which the specified value is to be associated.
-
value - value to be associated with the specified key.
-
Throws:
-
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.
get
public abstract String get(String key,
String def)
-
Returns the value associated with the specified key in this preference node. Returns the specified default if there is no value associated with the key, or the backing store is inaccessible.
Some implementations may store default values in their backing stores. If there is no value associated with the specified key but there is such a
stored default
, it is returned in preference to the specified default.
-
-
Parameters:
-
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
.
-
Returns:
-
the value associated with
key
, or
def
if no value is associated with
key
, or the backing store is inaccessible.
-
Throws:
-
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.)
remove
public abstract void remove(String key)
-
Removes the value associated with the specified key in this preference node, if any.
If this implementation supports
stored defaults
, and there is such a default for the specified preference, the stored default will be "exposed" by this call, in the sense that it will be returned by a succeeding call to
get
.
-
-
Parameters:
-
key - key whose mapping is to be removed from the preference node.
-
Throws:
-
NullPointerException
- if
key
is
null
.
-
IllegalStateException
- if this node (or an ancestor) has been removed with the
removeNode()
method.
clear
public abstract void clear()
throws BackingStoreException
-
Removes all of the preferences (key-value associations) in this preference node. This call has no effect on any descendants of this node.
If this implementation supports
stored defaults
, and this node in the preferences hierarchy contains any such defaults, the stored defaults will be "exposed" by this call, in the sense that they will be returned by succeeding calls to
get
.
-
-
Throws:
-
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.
-
See Also:
-
removeNode()
putInt
public abstract void putInt(String key,
int value)
-
Associates a string representing the specified int value with the specified key in this preference node. The associated string is the one that would be returned if the int value were passed to
Integer.toString(int)
. This method is intended for use in conjunction with
getInt(java.lang.String, int)
.
-
-
Parameters:
-
key - key with which the string form of value is to be associated.
-
value - value whose string form is to be associated with key.
-
Throws:
-
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.
-
See Also:
-
getInt(String,int)
getInt
public abstract int getInt(String key,
int def)
-
Returns the int value represented by the string associated with the specified key in this preference node. The string is converted to an integer as by
Integer.parseInt(String)
. Returns the specified default if there is no value associated with the key, the backing store is inaccessible, or if
Integer.parseInt(String)
would throw a
NumberFormatException
if the associated value were passed. This method is intended for use in conjunction with
putInt(java.lang.String, int)
.
If the implementation supports
stored defaults
and such a default exists, is accessible, and could be converted to an int with
Integer.parseInt
, this int is returned in preference to the specified default.
-
-
Parameters:
-
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, or the backing store is inaccessible.
-
Returns:
-
the int value represented by the string associated with
key
in this preference node, or
def
if the associated value does not exist or cannot be interpreted as an int.
-
Throws:
-
IllegalStateException
- if this node (or an ancestor) has been removed with the
removeNode()
method.
-
NullPointerException
- if
key
is
null
.
-
See Also:
-
putInt(String,int)
,
get(String,String)
putLong
public abstract void putLong(String key,
long value)
-
Associates a string representing the specified long value with the specified key in this preference node. The associated string is the one that would be returned if the long value were passed to
Long.toString(long)
. This method is intended for use in conjunction with
getLong(java.lang.String, long)
.
-
-
Parameters:
-
key - key with which the string form of value is to be associated.
-
value - value whose string form is to be associated with key.
-
Throws:
-
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.
-
See Also:
-
getLong(String,long)
getLong
public abstract long getLong(String key,
long def)
-
Returns the long value represented by the string associated with the specified key in this preference node. The string is converted to a long as by
Long.parseLong(String)
. Returns the specified default if there is no value associated with the key, the backing store is inaccessible, or if
Long.parseLong(String)
would throw a
NumberFormatException
if the associated value were passed. This method is intended for use in conjunction with
putLong(java.lang.String, long)
.
If the implementation supports
stored defaults
and such a default exists, is accessible, and could be converted to a long with
Long.parseLong
, this long is returned in preference to the specified default.
-
-
Parameters:
-
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, or the backing store is inaccessible.
-
Returns:
-
the long value represented by the string associated with
key
in this preference node, or
def
if the associated value does not exist or cannot be interpreted as a long.
-
Throws:
-
IllegalStateException
- if this node (or an ancestor) has been removed with the
removeNode()
method.
-
NullPointerException
- if
key
is
null
.
-
See Also:
-
putLong(String,long)
,
get(String,String)
putBoolean
public abstract void putBoolean(String key,
boolean value)
-
Associates a string representing the specified boolean value with the specified key in this preference node. The associated string is
"true"
if the value is true, and
"false"
if it is false. This method is intended for use in conjunction with
getBoolean(java.lang.String, boolean)
.
-
-
Parameters:
-
key - key with which the string form of value is to be associated.
-
value - value whose string form is to be associated with key.
-
Throws:
-
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.
-
See Also:
-
getBoolean(String,boolean)
,
get(String,String)
getBoolean
public abstract boolean getBoolean(String key,
boolean def)
-
Returns the boolean value represented by the string associated with the specified key in this preference node. Valid strings are
"true"
, which represents true, and
"false"
, which represents false. Case is ignored, so, for example,
"TRUE"
and
"False"
are also valid. This method is intended for use in conjunction with
putBoolean(java.lang.String, boolean)
.
Returns the specified default if there is no value associated with the key, the backing store is inaccessible, or if the associated value is something other than
"true"
or
"false"
, ignoring case.
If the implementation supports
stored defaults
and such a default exists and is accessible, it is used in preference to the specified default, unless the stored default is something other than
"true"
or
"false"
, ignoring case, in which case the specified default is used.
-
-
Parameters:
-
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, or the backing store is inaccessible.
-
Returns:
-
the boolean value represented by the string associated with
key
in this preference node, or
def
if the associated value does not exist or cannot be interpreted as a boolean.
-
Throws:
-
IllegalStateException
- if this node (or an ancestor) has been removed with the
removeNode()
method.
-
NullPointerException
- if
key
is
null
.
-
See Also:
-
get(String,String)
,
putBoolean(String,boolean)
putFloat
public abstract void putFloat(String key,
float value)
-
Associates a string representing the specified float value with the specified key in this preference node. The associated string is the one that would be returned if the float value were passed to
Float.toString(float)
. This method is intended for use in conjunction with
getFloat(java.lang.String, float)
.
-
-
Parameters:
-
key - key with which the string form of value is to be associated.
-
value - value whose string form is to be associated with key.
-
Throws:
-
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.
-
See Also:
-
getFloat(String,float)
getFloat
public abstract float getFloat(String key,
float def)
-
Returns the float value represented by the string associated with the specified key in this preference node. The string is converted to an integer as by
Float.parseFloat(String)
. Returns the specified default if there is no value associated with the key, the backing store is inaccessible, or if
Float.parseFloat(String)
would throw a
NumberFormatException
if the associated value were passed. This method is intended for use in conjunction with
putFloat(java.lang.String, float)
.
If the implementation supports
stored defaults
and such a default exists, is accessible, and could be converted to a float with
Float.parseFloat
, this float is returned in preference to the specified default.
-
-
Parameters:
-
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, or the backing store is inaccessible.
-
Returns:
-
the float value represented by the string associated with
key
in this preference node, or
def
if the associated value does not exist or cannot be interpreted as a float.
-
Throws:
-
IllegalStateException
- if this node (or an ancestor) has been removed with the
removeNode()
method.
-
NullPointerException
- if
key
is
null
.
-
See Also:
-
putFloat(String,float)
,
get(String,String)
putDouble
public abstract void putDouble(String key,
double value)
-
Associates a string representing the specified double value with the specified key in this preference node. The associated string is the one that would be returned if the double value were passed to
Double.toString(double)
. This method is intended for use in conjunction with
getDouble(java.lang.String, double)
.
-
-
Parameters:
-
key - key with which the string form of value is to be associated.
-
value - value whose string form is to be associated with key.
-
Throws:
-
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.
-
See Also:
-
getDouble(String,double)
getDouble
public abstract double getDouble(String key,
double def)
-
Returns the double value represented by the string associated with the specified key in this preference node. The string is converted to an integer as by
Double.parseDouble(String)
. Returns the specified default if there is no value associated with the key, the backing store is inaccessible, or if
Double.parseDouble(String)
would throw a
NumberFormatException
if the associated value were passed. This method is intended for use in conjunction with
putDouble(java.lang.String, double)
.
If the implementation supports
stored defaults
and such a default exists, is accessible, and could be converted to a double with
Double.parseDouble
, this double is returned in preference to the specified default.
-
-
Parameters:
-
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, or the backing store is inaccessible.
-
Returns:
-
the double value represented by the string associated with
key
in this preference node, or
def
if the associated value does not exist or cannot be interpreted as a double.
-
Throws:
-
IllegalStateException
- if this node (or an ancestor) has been removed with the
removeNode()
method.
-
NullPointerException
- if
key
is
null
.
-
See Also:
-
putDouble(String,double)
,
get(String,String)
putByteArray
public abstract void putByteArray(String key,
byte[] value)
-
Associates a string representing the specified byte array with the specified key in this preference node. The associated string is the
Base64
encoding of the byte array, as defined in
RFC 2045
, Section 6.8, with one minor change: the string will consist solely of characters from the
Base64 Alphabet
; it will not contain any newline characters. Note that the maximum length of the byte array is limited to three quarters of
MAX_VALUE_LENGTH
so that the length of the Base64 encoded String does not exceed
MAX_VALUE_LENGTH
. This method is intended for use in conjunction with
getByteArray(java.lang.String, byte[])
.
-
-
Parameters:
-
key - key with which the string form of value is to be associated.
-
value - value whose string form is to be associated with key.
-
Throws:
-
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.
-
See Also:
-
getByteArray(String,byte[])
,
get(String,String)
getByteArray
public abstract byte[] getByteArray(String key,
byte[] def)
-
Returns the byte array value represented by the string associated with the specified key in this preference node. Valid strings are
Base64
encoded binary data, as defined in
RFC 2045
, Section 6.8, with one minor change: the string must consist solely of characters from the
Base64 Alphabet
; no newline characters or extraneous characters are permitted. This method is intended for use in conjunction with
putByteArray(java.lang.String, byte[])
.
Returns the specified default if there is no value associated with the key, the backing store is inaccessible, or if the associated value is not a valid Base64 encoded byte array (as defined above).
If the implementation supports
stored defaults
and such a default exists and is accessible, it is used in preference to the specified default, unless the stored default is not a valid Base64 encoded byte array (as defined above), in which case the specified default is used.
-
-
Parameters:
-
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, or the backing store is inaccessible.
-
Returns:
-
the byte array value represented by the string associated with
key
in this preference node, or
def
if the associated value does not exist or cannot be interpreted as a byte array.
-
Throws:
-
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.)
-
See Also:
-
get(String,String)
,
putByteArray(String,byte[])
keys
public abstract String[] keys()
throws BackingStoreException
-
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.)
If the implementation supports
stored defaults
and there are any such defaults at this node that have not been overridden, by explicit preferences, the defaults are returned in the array in addition to any explicit preferences.
-
-
Returns:
-
an array of the keys that have an associated value in this preference node.
-
Throws:
-
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.
childrenNames
public abstract String[] childrenNames()
throws BackingStoreException
-
Returns the names of the children of this preference node, relative to this node. (The returned array will be of size zero if this node has no children.)
-
-
Returns:
-
the names of the children of this preference node.
-
Throws:
-
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.
parent
public abstract Preferences parent()
-
Returns the parent of this preference node, or
null
if this is the root.
-
-
Returns:
-
the parent of this preference node.
-
Throws:
-
IllegalStateException
- if this node (or an ancestor) has been removed with the
removeNode()
method.
node
public abstract Preferences node(String pathName)
-
Returns the named preference node in the same tree as this node, creating it and any of its ancestors if they do not already exist. Accepts a relative or absolute path name. Relative path names (which do not begin with the slash character
('/')
) are interpreted relative to this preference node.
If the returned node did not exist prior to this call, this node and any ancestors that were created by this call are not guaranteed to become permanent until the
flush
method is called on the returned node (or one of its ancestors or descendants).
-
-
Parameters:
-
pathName - the path name of the preference node to return.
-
Returns:
-
the specified preference node.
-
Throws:
-
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).
-
NullPointerException
- if path name is
null
.
-
IllegalStateException
- if this node (or an ancestor) has been removed with the
removeNode()
method.
-
See Also:
-
flush()
nodeExists
public abstract boolean nodeExists(String pathName)
throws BackingStoreException
-
Returns true if the named preference node exists in the same tree as this node. Relative path names (which do not begin with the slash character
('/')
) are interpreted relative to this preference node.
If this node (or an ancestor) has already been removed with the
removeNode()
method, it
is
legal to invoke this method, but only with the path name
""
; the invocation will return
false
. Thus, the idiom
p.nodeExists("")
may be used to test whether
p
has been removed.
-
-
Parameters:
-
pathName - the path name of the node whose existence is to be checked.
-
Returns:
-
true if the specified node exists.
-
Throws:
-
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).
-
NullPointerException
- if path name is
null
.
-
IllegalStateException
.s * @throws IllegalStateException if this node (or an ancestor) has been removed with the
removeNode()
- if this node (or an ancestor) has been removed with the
removeNode()
method and
pathName
is not the empty string (
""
).
removeNode
public abstract void removeNode()
throws BackingStoreException
-
Removes this preference node and all of its descendants, invalidating any preferences contained in the removed nodes. Once a node has been removed, attempting any method other than
name()
,
absolutePath()
,
isUserNode()
,
flush()
or
nodeExists("")
on the corresponding
Preferences
instance will fail with an
IllegalStateException
. (The methods defined on
Object
can still be invoked on a node after it has been removed; they will not throw
IllegalStateException
.)
The removal is not guaranteed to be persistent until the
flush
method is called on this node (or an ancestor).
If this implementation supports
stored defaults
, removing a node exposes any stored defaults at or below this node. Thus, a subsequent call to
nodeExists
on this node's path name may return
true
, and a subsequent call to
node
on this path name may return a (different)
Preferences
instance representing a non-empty collection of preferences and/or children.
-
-
Throws:
-
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 already been removed with the
removeNode()
method.
-
UnsupportedOperationException
- if this method is invoked on the root node.
-
See Also:
-
flush()
name
public abstract String name()
-
Returns this preference node's name, relative to its parent.
-
-
Returns:
-
this preference node's name, relative to its parent.
absolutePath
public abstract String absolutePath()
-
Returns this preference node's absolute path name.
-
-
Returns:
-
this preference node's absolute path name.
isUserNode
public abstract boolean isUserNode()
-
Returns
true
if this preference node is in the user preference tree,
false
if it's in the system preference tree.
-
-
Returns:
-
true
if this preference node is in the user preference tree,
false
if it's in the system preference tree.
toString
public abstract String toString()
-
Returns a string representation of this preferences node, as if computed by the expression:
(this.isUserNode() ? "User" : "System") + " Preference Node: " + this.absolutePath()
.
-
-
Overrides:
-
toString
in class
Object
-
-
Returns:
-
a string representation of the object.
flush
public abstract void flush()
throws BackingStoreException
-
Forces any changes in the contents of this preference node and its descendants to the persistent store. Once this method returns successfully, it is safe to assume that all changes made in the subtree rooted at this node prior to the method invocation have become permanent.
Implementations are free to flush changes into the persistent store at any time. They do not need to wait for this method to be called.
When a flush occurs on a newly created node, it is made persistent, as are any ancestors (and descendants) that have yet to be made persistent. Note however that any preference value changes in ancestors are
not
guaranteed to be made persistent.
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.
-
-
Throws:
-
BackingStoreException
- if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it.
-
See Also:
-
sync()
sync
public abstract void sync()
throws BackingStoreException
-
Ensures that future reads from this preference node and its descendants reflect any changes that were committed to the persistent store (from any VM) prior to the
sync
invocation. As a side-effect, forces any changes in the contents of this preference node and its descendants to the persistent store, as if the
flush
method had been invoked on this node.
-
-
Throws:
-
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.
-
See Also:
-
flush()
addPreferenceChangeListener
public abstract void addPreferenceChangeListener(PreferenceChangeListener pcl)
-
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.
-
-
Parameters:
-
pcl - The preference change listener to add.
-
Throws:
-
NullPointerException
- if
pcl
is null.
-
IllegalStateException
- if this node (or an ancestor) has been removed with the
removeNode()
method.
-
See Also:
-
removePreferenceChangeListener(PreferenceChangeListener)
,
addNodeChangeListener(NodeChangeListener)
removePreferenceChangeListener
public abstract void removePreferenceChangeListener(PreferenceChangeListener pcl)
-
Removes the specified preference change listener, so it no longer receives preference change events.
-
-
Parameters:
-
pcl - The preference change listener to remove.
-
Throws:
-
IllegalArgumentException
- if
pcl
was not a registered preference change listener on this node.
-
IllegalStateException
- if this node (or an ancestor) has been removed with the
removeNode()
method.
-
See Also:
-
addPreferenceChangeListener(PreferenceChangeListener)
addNodeChangeListener
public abstract void addNodeChangeListener(NodeChangeListener ncl)
-
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.
-
-
Parameters:
-
ncl - The
NodeChangeListener
to add.
-
Throws:
-
NullPointerException
- if
ncl
is null.
-
IllegalStateException
- if this node (or an ancestor) has been removed with the
removeNode()
method.
-
See Also:
-
removeNodeChangeListener(NodeChangeListener)
,
addPreferenceChangeListener(PreferenceChangeListener)
removeNodeChangeListener
public abstract void removeNodeChangeListener(NodeChangeListener ncl)
-
Removes the specified
NodeChangeListener
, so it no longer receives change events.
-
-
Parameters:
-
ncl - The
NodeChangeListener
to remove.
-
Throws:
-
IllegalArgumentException
- if
ncl
was not a registered
NodeChangeListener
on this node.
-
IllegalStateException
- if this node (or an ancestor) has been removed with the
removeNode()
method.
-
See Also:
-
addNodeChangeListener(NodeChangeListener)
exportNode
public abstract void exportNode(OutputStream os)
throws IOException,
BackingStoreException
-
Emits on the specified output stream an XML document representing all of the preferences contained in this node (but not its descendants). This XML document is, in effect, an offline backup of the node.
The XML document will have the following DOCTYPE declaration:
<!DOCTYPE preferences SYSTEM "http://java.sun.com/dtd/preferences.dtd">
The UTF-8 character encoding will be used.
This method is an exception to the general rule that the results of concurrently executing multiple methods in this class yields results equivalent to some serial execution. If the preferences at this node are modified concurrently with an invocation of this method, the exported preferences comprise a "fuzzy snapshot" of the preferences contained in the node; some of the concurrent modifications may be reflected in the exported data while others may not.
-
-
Parameters:
-
os - the output stream on which to emit the XML document.
-
Throws:
-
IOException
- if writing to the specified output stream results in an
IOException
.
-
BackingStoreException
- if preference data cannot be read from backing store.
-
IllegalStateException
- if this node (or an ancestor) has been removed with the
removeNode()
method.
-
See Also:
-
importPreferences(InputStream)
exportSubtree
public abstract void exportSubtree(OutputStream os)
throws IOException,
BackingStoreException
-
Emits an XML document representing all of the preferences contained in this node and all of its descendants. This XML document is, in effect, an offline backup of the subtree rooted at the node.
The XML document will have the following DOCTYPE declaration:
<!DOCTYPE preferences SYSTEM "http://java.sun.com/dtd/preferences.dtd">
The UTF-8 character encoding will be used.
This method is an exception to the general rule that the results of concurrently executing multiple methods in this class yields results equivalent to some serial execution. If the preferences or nodes in the subtree rooted at this node are modified concurrently with an invocation of this method, the exported preferences comprise a "fuzzy snapshot" of the subtree; some of the concurrent modifications may be reflected in the exported data while others may not.
-
-
Parameters:
-
os - the output stream on which to emit the XML document.
-
Throws:
-
IOException
- if writing to the specified output stream results in an
IOException
.
-
BackingStoreException
- if preference data cannot be read from backing store.
-
IllegalStateException
- if this node (or an ancestor) has been removed with the
removeNode()
method.
-
See Also:
-
importPreferences(InputStream)
,
exportNode(OutputStream)
importPreferences
public static void importPreferences(InputStream is)
throws IOException,
InvalidPreferencesFormatException
-
Imports all of the preferences represented by the XML document on the specified input stream. The document may represent user preferences or system preferences. If it represents user preferences, the preferences will be imported into the calling user's preference tree (even if they originally came from a different user's preference tree). If any of the preferences described by the document inhabit preference nodes that do not exist, the nodes will be created.
The XML document must have the following DOCTYPE declaration:
<!DOCTYPE preferences SYSTEM "http://java.sun.com/dtd/preferences.dtd">
(This method is designed for use in conjunction with
exportNode(OutputStream)
and
exportSubtree(OutputStream)
.
This method is an exception to the general rule that the results of concurrently executing multiple methods in this class yields results equivalent to some serial execution. The method behaves as if implemented on top of the other public methods in this class, notably
node(String)
and
put(String, String)
.
-
-
Parameters:
-
is - the input stream from which to read the XML document.
-
Throws:
-
IOException
- if reading from the specified
input
output
stream results in an
IOException
.-
InvalidPreferencesFormatException
- Data on input stream does not constitute a valid XML document with the mandated document type.
-
SecurityException
- If a security manager is present and it denies
RuntimePermission("preferences")
.
-
See Also:
-
RuntimePermission