Class Preferences

java.lang.Object
java.util.prefs.Preferences
Direct Known Subclasses:
AbstractPreferences
public abstract classPreferencesextendsObject
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 anode name (which is not necessarily unique), a uniqueabsolute path name, and a path namerelative 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 noden's path name relative to its ancestora is simply the string that must be appended toa's absolute path name in order to formn'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. Theflush method may be used to synchronously force updates to the backing store. Normal termination of the Java Virtual Machine willnot result in the loss of pending updates -- an explicitflush invocation isnot required upon termination to ensure that pending updates are made persistent.

All of the methods that read preferences from aPreferences object require the invoker to provide a default value. The default value is returned if no value has been previously setor 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, likeflush, 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 throwBackingStoreException.

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 concurrentlyby 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) isnot 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 >
EveryPreferences implementation must have an associatedPreferencesFactory implementation. Every Java(TM) SE implementation must provide some means of specifying whichPreferencesFactory 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:
ThePreferencesFactory implementation is located as follows:

  1. If the system propertyjava.util.prefs.PreferencesFactory is defined, then it is taken to be the fully-qualified name of a class implementing thePreferencesFactory interface. The class is loaded and instantiated; if this process fails then an unspecified error is thrown.

  2. If aPreferencesFactory implementation class file has been installed in a jar file that is visible to thesystem class loader, and that jar file contains a provider-configuration file namedjava.util.prefs.PreferencesFactory in the resource directoryMETA-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 defaultPreferencesFactory implementation for the underlying platform is loaded and instantiated.

Since:
1.4

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final int
    Maximum length of string allowed as a key (80 characters).
    static final int
    Maximum length of a node name (80 characters).
    static final int
    Maximum length of string allowed as a value (8192 characters).

  • Constructor Summary

    Constructors
    Modifier
    Constructor
    Description
    protected
    Sole constructor.

  • Method Summary

    Modifier and Type
    Method
    Description
    abstractString
    Returns this preference node's absolute path name.
    abstract void
    Registers the specified listener to receivenode change events for this node.
    abstract void
    Registers the specified listener to receivepreference change events for this preference node.
    abstractString[]
    Returns the names of the children of this preference node, relative to this node.
    abstract void
    Removes all of the preferences (key-value associations) in this preference node.
    abstract void
    Emits on the specified output stream an XML document representing all of the preferences contained in this node (but not its descendants).
    abstract void
    Emits an XML document representing all of the preferences contained in this node and all of its descendants.
    abstract void
    Forces any changes in the contents of this preference node and its descendants to the persistent store.
    abstractString
    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
    Imports all of the preferences represented by the XML document on the specified input stream.
    abstract boolean
    Returnstrue if this preference node is in the user preference tree,false if it's in the system preference tree.
    abstractString[]
    Returns all of the keys that have an associated value in this preference node.
    abstractString
    Returns this preference node's name, relative to its parent.
    abstractPreferences
    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.
    abstractPreferences
    Returns the parent of this preference node, ornull 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
    Removes the value associated with the specified key in this preference node, if any.
    abstract void
    Removes this preference node and all of its descendants, invalidating any preferences contained in the removed nodes.
    abstract void
    Removes the specifiedNodeChangeListener, so it no longer receives change events.
    abstract void
    Removes the specified preference change listener, so it no longer receives preference change events.
    abstract void
    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 thesync invocation.
    Returns the preference node from the system preference tree that is associated (by convention) with the specified class's package.
    Returns the root preference node for the system.
    abstractString
    Returns a string representation of this preferences node, as if computed by the expression:(this.isUserNode() ? "User" : "System") + " Preference Node: " + this.absolutePath().
    Returns the preference node from the calling user's preference tree that is associated (by convention) with the specified class's package.
    Returns the root preference node for the calling user.

    Methods declared in class java.lang.Object

    clone,equals,finalize,getClass,hashCode,notify,notifyAll,wait,wait,wait

  • Field Details

    • MAX_KEY_LENGTH

      public static final int MAX_KEY_LENGTH
      Maximum length of string allowed as a key (80 characters).
      See Also:

    • MAX_VALUE_LENGTH

      public static final int MAX_VALUE_LENGTH
      Maximum length of string allowed as a value (8192 characters).
      See Also:

    • MAX_NAME_LENGTH

      public static final int MAX_NAME_LENGTH
      Maximum length of a node name (80 characters).
      See Also:

  • Constructor Details

    • Preferences

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

  • Method Details

    • 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 classcom.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 classFoo 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 theflush 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 whichc is a member.
      Throws:
      NullPointerException - ifc isnull.

    • 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 classcom.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 classFoo 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 theflush 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 whichc is a member.
      Throws:
      NullPointerException - ifc isnull.

    • userRoot

      public static Preferences userRoot()
      Returns the root preference node for the calling user.
      Returns:
      the root preference node for the calling user.

    • systemRoot

      public static Preferences systemRoot()
      Returns the root preference node for the system.
      Returns:
      the root preference node for the system.

    • 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 isnull.
      IllegalArgumentException - ifkey.length() exceedsMAX_KEY_LENGTH or ifvalue.length exceedsMAX_VALUE_LENGTH.
      IllegalStateException - if this node (or an ancestor) has been removed with theremoveNode() method.
      IllegalArgumentException - if either key or value contain the null control character, code point U+0000.

    • 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 astored 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 withkey.
      Returns:
      the value associated withkey, ordef if no value is associated withkey, or the backing store is inaccessible.
      Throws:
      IllegalStateException - if this node (or an ancestor) has been removed with theremoveNode() method.
      NullPointerException - ifkey isnull. (Anull value fordefis permitted.)
      IllegalArgumentException - if key contains the null control character, code point U+0000.

    • remove

      public abstract void remove(String key)
      Removes the value associated with the specified key in this preference node, if any.

      If this implementation supportsstored 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 toget.

      Parameters:
      key - key whose mapping is to be removed from the preference node.
      Throws:
      NullPointerException - ifkey isnull.
      IllegalStateException - if this node (or an ancestor) has been removed with theremoveNode() method.
      IllegalArgumentException - if key contains the null control character, code point U+0000.

    • clear

      public abstract void clear() throwsBackingStoreException
      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 supportsstored 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 toget.

      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 theremoveNode() method.
      See Also:

    • 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 toInteger.toString(int). This method is intended for use in conjunction withgetInt(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 - ifkey isnull.
      IllegalArgumentException - ifkey.length() exceedsMAX_KEY_LENGTH.
      IllegalStateException - if this node (or an ancestor) has been removed with theremoveNode() method.
      IllegalArgumentException - if key contains the null control character, code point U+0000.
      See Also:

    • 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 byInteger.parseInt(String). Returns the specified default if there is no value associated with the key, the backing store is inaccessible, or ifInteger.parseInt(String) would throw aNumberFormatException if the associated value were passed. This method is intended for use in conjunction withputInt(java.lang.String, int).

      If the implementation supportsstored defaults and such a default exists, is accessible, and could be converted to an int withInteger.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 withkey 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 withkey in this preference node, ordef 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 theremoveNode() method.
      NullPointerException - ifkey isnull.
      IllegalArgumentException - if key contains the null control character, code point U+0000.
      See Also:

    • 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 toLong.toString(long). This method is intended for use in conjunction withgetLong(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 - ifkey isnull.
      IllegalArgumentException - ifkey.length() exceedsMAX_KEY_LENGTH.
      IllegalStateException - if this node (or an ancestor) has been removed with theremoveNode() method.
      IllegalArgumentException - if key contains the null control character, code point U+0000.
      See Also:

    • 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 byLong.parseLong(String). Returns the specified default if there is no value associated with the key, the backing store is inaccessible, or ifLong.parseLong(String) would throw aNumberFormatException if the associated value were passed. This method is intended for use in conjunction withputLong(java.lang.String, long).

      If the implementation supportsstored defaults and such a default exists, is accessible, and could be converted to a long withLong.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 withkey 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 withkey in this preference node, ordef 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 theremoveNode() method.
      NullPointerException - ifkey isnull.
      IllegalArgumentException - if key contains the null control character, code point U+0000.
      See Also:

    • 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 withgetBoolean(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 - ifkey isnull.
      IllegalArgumentException - ifkey.length() exceedsMAX_KEY_LENGTH.
      IllegalStateException - if this node (or an ancestor) has been removed with theremoveNode() method.
      IllegalArgumentException - if key contains the null control character, code point U+0000.
      See Also:

    • 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 withputBoolean(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 supportsstored 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 withkey 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 withkey in this preference node, ordef 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 theremoveNode() method.
      NullPointerException - ifkey isnull.
      IllegalArgumentException - if key contains the null control character, code point U+0000.
      See Also:

    • 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 toFloat.toString(float). This method is intended for use in conjunction withgetFloat(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 - ifkey isnull.
      IllegalArgumentException - ifkey.length() exceedsMAX_KEY_LENGTH.
      IllegalStateException - if this node (or an ancestor) has been removed with theremoveNode() method.
      IllegalArgumentException - if key contains the null control character, code point U+0000.
      See Also:

    • 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 byFloat.parseFloat(String). Returns the specified default if there is no value associated with the key, the backing store is inaccessible, or ifFloat.parseFloat(String) would throw aNumberFormatException if the associated value were passed. This method is intended for use in conjunction withputFloat(java.lang.String, float).

      If the implementation supportsstored defaults and such a default exists, is accessible, and could be converted to a float withFloat.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 withkey 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 withkey in this preference node, ordef 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 theremoveNode() method.
      NullPointerException - ifkey isnull.
      IllegalArgumentException - if key contains the null control character, code point U+0000.
      See Also:

    • 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 toDouble.toString(double). This method is intended for use in conjunction withgetDouble(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 - ifkey isnull.
      IllegalArgumentException - ifkey.length() exceedsMAX_KEY_LENGTH.
      IllegalStateException - if this node (or an ancestor) has been removed with theremoveNode() method.
      IllegalArgumentException - if key contains the null control character, code point U+0000.
      See Also:

    • 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 byDouble.parseDouble(String). Returns the specified default if there is no value associated with the key, the backing store is inaccessible, or ifDouble.parseDouble(String) would throw aNumberFormatException if the associated value were passed. This method is intended for use in conjunction withputDouble(java.lang.String, double).

      If the implementation supportsstored defaults and such a default exists, is accessible, and could be converted to a double withDouble.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 withkey 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 withkey in this preference node, ordef 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 theremoveNode() method.
      NullPointerException - ifkey isnull.
      IllegalArgumentException - if key contains the null control character, code point U+0000.
      See Also:

    • 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 theBase64 encoding of the byte array, as defined inRFC 2045, Section 6.8, with one minor change: the string will consist solely of characters from theBase64 Alphabet; it will not contain any newline characters. Note that the maximum length of the byte array is limited to three quarters ofMAX_VALUE_LENGTH so that the length of the Base64 encoded String does not exceedMAX_VALUE_LENGTH. This method is intended for use in conjunction withgetByteArray(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 isnull.
      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 theremoveNode() method.
      IllegalArgumentException - if key contains the null control character, code point U+0000.
      See Also:

    • 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 areBase64 encoded binary data, as defined inRFC 2045, Section 6.8, with one minor change: the string must consist solely of characters from theBase64 Alphabet; no newline characters or extraneous characters are permitted. This method is intended for use in conjunction withputByteArray(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 supportsstored 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 withkey 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 withkey in this preference node, ordef 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 theremoveNode() method.
      NullPointerException - ifkey isnull. (Anull value fordefis permitted.)
      IllegalArgumentException - if key contains the null control character, code point U+0000.
      See Also:

    • keys

      public abstract String[] keys() throwsBackingStoreException
      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 supportsstored 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 theremoveNode() method.

    • childrenNames

      public abstract String[] childrenNames() throwsBackingStoreException
      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 theremoveNode() method.

    • parent

      public abstract Preferences parent()
      Returns the parent of this preference node, ornull if this is the root.
      Returns:
      the parent of this preference node.
      Throws:
      IllegalStateException - if this node (or an ancestor) has been removed with theremoveNode() 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 theflush 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 isnull.
      IllegalStateException - if this node (or an ancestor) has been removed with theremoveNode() method.
      See Also:

    • nodeExists

      public abstract boolean nodeExists(String pathName) throwsBackingStoreException
      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 theremoveNode() method, itis legal to invoke this method, but only with the path name""; the invocation will returnfalse. Thus, the idiomp.nodeExists("") may be used to test whetherp 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 isnull.
      IllegalStateException - if this node (or an ancestor) has been removed with theremoveNode() method andpathName is not the empty string ("").

    • removeNode

      public abstract void removeNode() throwsBackingStoreException
      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 thanname(),absolutePath(),isUserNode(),flush() ornodeExists("") on the correspondingPreferences instance will fail with anIllegalStateException. (The methods defined onObject can still be invoked on a node after it has been removed; they will not throwIllegalStateException.)

      The removal is not guaranteed to be persistent until theflush method is called on this node (or an ancestor).

      If this implementation supportsstored defaults, removing a node exposes any stored defaults at or below this node. Thus, a subsequent call tonodeExists on this node's path name may returntrue, and a subsequent call tonode 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 theremoveNode() method.
      UnsupportedOperationException - if this method is invoked on the root node.
      See Also:

    • 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()
      Returnstrue 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() throwsBackingStoreException
      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 arenot guaranteed to be made persistent.

      If this method is invoked on a node that has been removed with theremoveNode() 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

      public abstract void sync() throwsBackingStoreException
      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 thesync invocation. As a side-effect, forces any changes in the contents of this preference node and its descendants to the persistent store, as if theflush 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 theremoveNode() method.
      See Also:

    • addPreferenceChangeListener

      public abstract void addPreferenceChangeListener(PreferenceChangeListener pcl)
      Registers the specified listener to receivepreference 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 arenot generated by theremoveNode() method, which generates anode change event. Preference change eventsare generated by theclear 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 - ifpcl is null.
      IllegalStateException - if this node (or an ancestor) has been removed with theremoveNode() method.
      See Also:

    • 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 - ifpcl was not a registered preference change listener on this node.
      IllegalStateException - if this node (or an ancestor) has been removed with theremoveNode() method.
      See Also:

    • addNodeChangeListener

      public abstract void addNodeChangeListener(NodeChangeListener ncl)
      Registers the specified listener to receivenode change events for this node. A node change event is generated when a child node is added to or removed from this node. (A singleremoveNode() invocation results in multiplenode 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 - TheNodeChangeListener to add.
      Throws:
      NullPointerException - ifncl is null.
      IllegalStateException - if this node (or an ancestor) has been removed with theremoveNode() method.
      See Also:

    • removeNodeChangeListener

      public abstract void removeNodeChangeListener(NodeChangeListener ncl)
      Removes the specifiedNodeChangeListener, so it no longer receives change events.
      Parameters:
      ncl - TheNodeChangeListener to remove.
      Throws:
      IllegalArgumentException - ifncl was not a registeredNodeChangeListener on this node.
      IllegalStateException - if this node (or an ancestor) has been removed with theremoveNode() method.
      See Also:

    • exportNode

      public abstract void exportNode(OutputStream os) throwsIOException,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 anIOException.
      BackingStoreException - if preference data cannot be read from backing store.
      IllegalStateException - if this node (or an ancestor) has been removed with theremoveNode() method.
      See Also:

    • exportSubtree

      public abstract void exportSubtree(OutputStream os) throwsIOException,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 anIOException.
      BackingStoreException - if preference data cannot be read from backing store.
      IllegalStateException - if this node (or an ancestor) has been removed with theremoveNode() method.
      See Also:

    • importPreferences

      public static void importPreferences(InputStream is) throwsIOException,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 withexportNode(OutputStream) andexportSubtree(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, notablynode(String) andput(String, String).

      Parameters:
      is - the input stream from which to read the XML document.
      Throws:
      IOException - if reading from the specified input stream results in anIOException.
      InvalidPreferencesFormatException - Data on input stream does not constitute a valid XML document with the mandated document type.