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Preferences

public abstract class Preferences
extends Object

java.lang.Object
   ↳ java.util.prefs.Preferences
Known Direct Subclasses


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 Java(TM) SE 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:

  1. 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.

  2. 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.

  3. 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.

Summary

Constants

int MAX_KEY_LENGTH

Maximum length of string allowed as a key (80 characters).

int MAX_NAME_LENGTH

Maximum length of a node name (80 characters).

int MAX_VALUE_LENGTH

Maximum length of string allowed as a value (8192 characters).

Protected constructors

Preferences()

Sole constructor.

Public methods

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)

WARNING: On Android, the Preference nodes corresponding to the "system" and "user" preferences are stored in sections of the file system that are inaccessible to apps.

static Preferences systemRoot()

WARNING: On Android, the Preference nodes corresponding to the "system" and "user" preferences are stored in sections of the file system that are inaccessible to apps.

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)

WARNING: On Android, the Preference nodes corresponding to the "system" and "user" preferences are stored in sections of the file system that are inaccessible to apps.

static Preferences userRoot()

WARNING: On Android, the Preference nodes corresponding to the "system" and "user" preferences are stored in sections of the file system that are inaccessible to apps.

Inherited methods

From class java.lang.Object

Constants

MAX_KEY_LENGTH

Added in API level 1
int MAX_KEY_LENGTH

Maximum length of string allowed as a key (80 characters).

Constant Value: 80 (0x00000050)

MAX_NAME_LENGTH

Added in API level 1
int MAX_NAME_LENGTH

Maximum length of a node name (80 characters).

Constant Value: 80 (0x00000050)

MAX_VALUE_LENGTH

Added in API level 1
int MAX_VALUE_LENGTH

Maximum length of string allowed as a value (8192 characters).

Constant Value: 8192 (0x00002000)

Protected constructors

Preferences

Added in API level 1
Preferences ()

Sole constructor. (For invocation by subclass constructors, typically implicit.)

Public methods

absolutePath

Added in API level 1
String absolutePath ()

Returns this preference node's absolute path name.

Returns
String this preference node's absolute path name.

addNodeChangeListener

Added in API level 1
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 NodeChangeListener: 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:

addPreferenceChangeListener

Added in API level 1
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 PreferenceChangeListener: 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:

childrenNames

Added in API level 1
String[] childrenNames ()

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
String[] 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.

clear

Added in API level 1
void clear ()

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:

exportNode

Added in API level 1
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). 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 OutputStream: 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:

exportSubtree

Added in API level 1
void exportSubtree (OutputStream os)

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 OutputStream: 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:

flush

Added in API level 1
void flush ()

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:

get

Added in API level 1
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 String: key whose associated value is to be returned.
def String: the value to be returned in the event that this preference node has no value associated with key.
Returns
String 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.)

getBoolean

Added in API level 1
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(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 String: key whose associated value is to be returned as a boolean.
def boolean: 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
boolean 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:

getByteArray

Added in API level 1
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(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 String: key whose associated value is to be returned as a byte array.
def byte: 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
byte[] 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:

getDouble

Added in API level 1
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 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(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 String: key whose associated value is to be returned as a double.
def double: 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
double 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:

getFloat

Added in API level 1
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 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(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 String: key whose associated value is to be returned as a float.
def float: 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
float 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:

getInt

Added in API level 1
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 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(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 String: key whose associated value is to be returned as an int.
def int: 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
int 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:

getLong

Added in API level 1
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 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(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 String: key whose associated value is to be returned as a long.
def long: 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
long 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:

importPreferences

Added in API level 1
void importPreferences (InputStream is)

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 InputStream: the input stream from which to read the XML document.
Throws
IOException if reading from the specified input 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:

isUserNode

Added in API level 1
boolean isUserNode ()

Returns true if this preference node is in the user preference tree, false if it's in the system preference tree.

Returns
boolean true if this preference node is in the user preference tree, false if it's in the system preference tree.

keys

Added in API level 1
String[] keys ()

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
String[] 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.

name

Added in API level 1
String name ()

Returns this preference node's name, relative to its parent.

Returns
String this preference node's name, relative to its parent.

node

Added in API level 1
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 String: the path name of the preference node to return.
Returns
Preferences 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:

nodeExists

Added in API level 1
boolean nodeExists (String pathName)

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 String: the path name of the node whose existence is to be checked.
Returns
boolean 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 if this node (or an ancestor) has been removed with the removeNode() method and pathName is not the empty string ("").

parent

Added in API level 1
Preferences parent ()

Returns the parent of this preference node, or null if this is the root.

Returns
Preferences the parent of this preference node.
Throws
IllegalStateException if this node (or an ancestor) has been removed with the removeNode() method.

put

Added in API level 1
void put (String key, 
                String value)

Associates the specified value with the specified key in this preference node.

Parameters
key String: key with which the specified value is to be associated.
value String: 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.

putBoolean

Added in API level 1
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(String, boolean).

Parameters
key String: key with which the string form of value is to be associated.
value boolean: 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:

putByteArray

Added in API level 1
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(String, byte[]).

Parameters
key String: key with which the string form of value is to be associated.
value byte: 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:

putDouble

Added in API level 1
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 toString(double). This method is intended for use in conjunction with getDouble(String, double).

Parameters
key String: key with which the string form of value is to be associated.
value double: 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:

putFloat

Added in API level 1
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 toString(float). This method is intended for use in conjunction with getFloat(String, float).

Parameters
key String: key with which the string form of value is to be associated.
value float: 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:

putInt

Added in API level 1
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 toString(int). This method is intended for use in conjunction with getInt(String, int).

Parameters
key String: key with which the string form of value is to be associated.
value int: 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:

putLong

Added in API level 1
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 toString(long). This method is intended for use in conjunction with getLong(String, long).

Parameters
key String: key with which the string form of value is to be associated.
value long: 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:

remove

Added in API level 1
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 String: 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.

removeNode

Added in API level 1
void removeNode ()

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:

removeNodeChangeListener

Added in API level 1
void removeNodeChangeListener (NodeChangeListener ncl)

Removes the specified NodeChangeListener, so it no longer receives change events.

Parameters
ncl NodeChangeListener: 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:

removePreferenceChangeListener

Added in API level 1
void removePreferenceChangeListener (PreferenceChangeListener pcl)

Removes the specified preference change listener, so it no longer receives preference change events.

Parameters
pcl PreferenceChangeListener: 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:

sync

Added in API level 1
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. 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:

systemNodeForPackage

Added in API level 1
Preferences systemNodeForPackage (Class<?> c)

WARNING: On Android, the Preference nodes corresponding to the "system" and "user" preferences are stored in sections of the file system that are inaccessible to apps. Further, allowing apps to set "system wide" preferences is contrary to android's security model. 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 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 Class: the class for whose package a system preference node is desired.
Returns
Preferences 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:

systemRoot

Added in API level 1
Preferences systemRoot ()

WARNING: On Android, the Preference nodes corresponding to the "system" and "user" preferences are stored in sections of the file system that are inaccessible to apps. Further, allowing apps to set "system wide" preferences is contrary to android's security model. Returns the root preference node for the system.

Returns
Preferences the root preference node for the system.
Throws
SecurityException If a security manager is present and it denies RuntimePermission("preferences").

See also:

toString

Added in API level 1
String toString ()

Returns a string representation of this preferences node, as if computed by the expression:(this.isUserNode() ? "User" : "System") + " Preference Node: " + this.absolutePath().

Returns
String a string representation of the object.

userNodeForPackage

Added in API level 1
Preferences userNodeForPackage (Class<?> c)

WARNING: On Android, the Preference nodes corresponding to the "system" and "user" preferences are stored in sections of the file system that are inaccessible to apps. Further, allowing apps to set "system wide" preferences is contrary to android's security model. 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 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 Class: the class for whose package a user preference node is desired.
Returns
Preferences 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:

userRoot

Added in API level 1
Preferences userRoot ()

WARNING: On Android, the Preference nodes corresponding to the "system" and "user" preferences are stored in sections of the file system that are inaccessible to apps. Further, allowing apps to set "system wide" preferences is contrary to android's security model. Returns the root preference node for the calling user.

Returns
Preferences the root preference node for the calling user.
Throws
SecurityException If a security manager is present and it denies RuntimePermission("preferences").

See also:

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