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Preferences.javaAPI DocJava SE 6 API59869Tue Jun 10 00:26:00 BST 2008java.util.prefs

Preferences

public abstract class Preferences extends Object
A node in a hierarchical collection of preference data. This class allows applications to store and retrieve user and system preference and configuration data. This data is stored persistently in an implementation-dependent backing store. Typical implementations include flat files, OS-specific registries, directory servers and SQL databases. The user of this class needn't be concerned with details of the backing store.

There are two separate trees of preference nodes, one for user preferences and one for system preferences. Each user has a separate user preference tree, and all users in a given system share the same system preference tree. The precise description of "user" and "system" will vary from implementation to implementation. Typical information stored in the user preference tree might include font choice, color choice, or preferred window location and size for a particular application. Typical information stored in the system preference tree might include installation configuration data for an application.

Nodes in a preference tree are named in a similar fashion to directories in a hierarchical file system. Every node in a preference tree has a node name (which is not necessarily unique), a unique absolute path name, and a path name relative to each ancestor including itself.

The root node has a node name of the empty string (""). Every other node has an arbitrary node name, specified at the time it is created. The only restrictions on this name are that it cannot be the empty string, and it cannot contain the slash character ('/').

The root node has an absolute path name of "/". Children of the root node have absolute path names of "/" + <node name>. All other nodes have absolute path names of <parent's absolute path name> + "/" + <node name>. Note that all absolute path names begin with the slash character.

A node n's path name relative to its ancestor a is simply the string that must be appended to a's absolute path name in order to form n's absolute path name, with the initial slash character (if present) removed. Note that:

  • No relative path names begin with the slash character.
  • Every node's path name relative to itself is the empty string.
  • Every node's path name relative to its parent is its node name (except for the root node, which does not have a parent).
  • Every node's path name relative to the root is its absolute path name with the initial slash character removed.

Note finally that:

  • No path name contains multiple consecutive slash characters.
  • No path name with the exception of the root's absolute path name ends in the slash character.
  • Any string that conforms to these two rules is a valid path name.

All of the methods that modify preferences data are permitted to operate asynchronously; they may return immediately, and changes will eventually propagate to the persistent backing store with an implementation-dependent delay. The flush method may be used to synchronously force updates to the backing store. Normal termination of the Java Virtual Machine will not result in the loss of pending updates -- an explicit flush invocation is not required upon termination to ensure that pending updates are made persistent.

All of the methods that read preferences from a Preferences object require the invoker to provide a default value. The default value is returned if no value has been previously set or if the backing store is unavailable. The intent is to allow applications to operate, albeit with slightly degraded functionality, even if the backing store becomes unavailable. Several methods, like flush, have semantics that prevent them from operating if the backing store is unavailable. Ordinary applications should have no need to invoke any of these methods, which can be identified by the fact that they are declared to throw {@link 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 {@link 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 {@link java.lang.ClassLoader#getSystemClassLoader 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.

author
Josh Bloch
version
1.30, 06/26/06
since
1.4

Fields Summary
private static final PreferencesFactory
factory
public static final int
MAX_KEY_LENGTH
Maximum length of string allowed as a key (80 characters).
public static final int
MAX_VALUE_LENGTH
Maximum length of string allowed as a value (8192 characters).
public static final int
MAX_NAME_LENGTH
Maximum length of a node name (80 characters).
private static Permission
prefsPerm
This permission object represents the permission required to get access to the user or system root (which in turn allows for all other operations).
Constructors Summary
protected Preferences()
Sole constructor. (For invocation by subclass constructors, typically implicit.)

    
Methods Summary
public abstract java.lang.StringabsolutePath()
Returns this preference node's absolute path name.

return
this preference node's absolute path name.

public abstract voidaddNodeChangeListener(java.util.prefs.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 {@link #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.

param
ncl The NodeChangeListener to add.
throws
NullPointerException if ncl is null.
throws
IllegalStateException if this node (or an ancestor) has been removed with the {@link #removeNode()} method.
see
#removeNodeChangeListener(NodeChangeListener)
see
#addPreferenceChangeListener(PreferenceChangeListener)

public abstract voidaddPreferenceChangeListener(java.util.prefs.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 {@link #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.

param
pcl The preference change listener to add.
throws
NullPointerException if pcl is null.
throws
IllegalStateException if this node (or an ancestor) has been removed with the {@link #removeNode()} method.
see
#removePreferenceChangeListener(PreferenceChangeListener)
see
#addNodeChangeListener(NodeChangeListener)

public abstract java.lang.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.)

return
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.
throws
IllegalStateException if this node (or an ancestor) has been removed with the {@link #removeNode()} method.

public abstract voidclear()
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.
throws
IllegalStateException if this node (or an ancestor) has been removed with the {@link #removeNode()} method.
see
#removeNode()

public abstract voidexportNode(java.io.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.

param
os the output stream on which to emit the XML document.
throws
IOException if writing to the specified output stream results in an IOException.
throws
BackingStoreException if preference data cannot be read from backing store.
see
#importPreferences(InputStream)
throws
IllegalStateException if this node (or an ancestor) has been removed with the {@link #removeNode()} method.

public abstract voidexportSubtree(java.io.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.

param
os the output stream on which to emit the XML document.
throws
IOException if writing to the specified output stream results in an IOException.
throws
BackingStoreException if preference data cannot be read from backing store.
throws
IllegalStateException if this node (or an ancestor) has been removed with the {@link #removeNode()} method.
see
#importPreferences(InputStream)
see
#exportNode(OutputStream)

private static java.util.prefs.PreferencesFactoryfactory()


        
	// 1. Try user-specified system property
	String factoryName = AccessController.doPrivileged(
	    new PrivilegedAction<String>() {
		public String run() {
		    return System.getProperty(
			"java.util.prefs.PreferencesFactory");}});
	if (factoryName != null) {
	    // FIXME: This code should be run in a doPrivileged and
	    // not use the context classloader, to avoid being
	    // dependent on the invoking thread.
	    // Checking AllPermission also seems wrong.
	    try {
		return (PreferencesFactory)
		    Class.forName(factoryName, false,
				  ClassLoader.getSystemClassLoader())
		    .newInstance();
	    } catch (Exception ex) {
		try {
		    // workaround for javaws, plugin,
		    // load factory class using non-system classloader
		    SecurityManager sm = System.getSecurityManager();
		    if (sm != null) {
			sm.checkPermission(new java.security.AllPermission());
		    }
		    return (PreferencesFactory)
			Class.forName(factoryName, false,
				      Thread.currentThread()
				      .getContextClassLoader())
			.newInstance();
		} catch (Exception e) {
		    InternalError error = new InternalError(
			"Can't instantiate Preferences factory "
			+ factoryName);
		    error.initCause(e);
		    throw error;
		}
	    }
	}

	return AccessController.doPrivileged(
	    new PrivilegedAction<PreferencesFactory>() {
		public PreferencesFactory run() {
		    return factory1();}});
    
private static java.util.prefs.PreferencesFactoryfactory1()

	// 2. Try service provider interface
	Iterator i = Service.providers(PreferencesFactory.class,
				       ClassLoader.getSystemClassLoader());
	// choose first provider instance
	while (i.hasNext()) {
	    try {
		return (PreferencesFactory) i.next();
	    } catch (ServiceConfigurationError sce) {
		if (sce.getCause() instanceof SecurityException) {
		    // Ignore the security exception, try the next provider
		    continue;
		}
		throw sce;
	    }
	}

	// 3. Use platform-specific system-wide default
	String platformFactory =
	    System.getProperty("os.name").startsWith("Windows")
	    ? "java.util.prefs.WindowsPreferencesFactory"
	    : "java.util.prefs.FileSystemPreferencesFactory";
	try {
	    return (PreferencesFactory)
		Class.forName(platformFactory, false, null).newInstance();
	} catch (Exception e) {
	    InternalError error = new InternalError(
		"Can't instantiate platform default Preferences factory "
		+ platformFactory);
	    error.initCause(e);
	    throw error;
	}
    
public abstract voidflush()
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 {@link #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
#sync()

public abstract java.lang.Stringget(java.lang.String key, java.lang.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.

param
key key whose associated value is to be returned.
param
def the value to be returned in the event that this preference node has no value associated with key.
return
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 {@link #removeNode()} method.
throws
NullPointerException if key is null. (A null value for def is permitted.)

public abstract booleangetBoolean(java.lang.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 {@link #putBoolean}.

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.

param
key key whose associated value is to be returned as a boolean.
param
def the value to be returned in the event that this preference node has no value associated with key or the associated value cannot be interpreted as a boolean, or the backing store is inaccessible.
return
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 {@link #removeNode()} method.
throws
NullPointerException if key is null.
see
#get(String,String)
see
#putBoolean(String,boolean)

public abstract byte[]getByteArray(java.lang.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 {@link #putByteArray}.

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.

param
key key whose associated value is to be returned as a byte array.
param
def the value to be returned in the event that this preference node has no value associated with key or the associated value cannot be interpreted as a byte array, or the backing store is inaccessible.
return
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 {@link #removeNode()} method.
throws
NullPointerException if key is null. (A null value for def is permitted.)
see
#get(String,String)
see
#putByteArray(String,byte[])

public abstract doublegetDouble(java.lang.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 {@link Double#parseDouble(String)}. Returns the specified default if there is no value associated with the key, the backing store is inaccessible, or if Double.parseDouble(String) would throw a {@link NumberFormatException} if the associated value were passed. This method is intended for use in conjunction with {@link #putDouble}.

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.

param
key key whose associated value is to be returned as a double.
param
def the value to be returned in the event that this preference node has no value associated with key or the associated value cannot be interpreted as a double, or the backing store is inaccessible.
return
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 {@link #removeNode()} method.
throws
NullPointerException if key is null.
see
#putDouble(String,double)
see
#get(String,String)

public abstract floatgetFloat(java.lang.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 {@link Float#parseFloat(String)}. Returns the specified default if there is no value associated with the key, the backing store is inaccessible, or if Float.parseFloat(String) would throw a {@link NumberFormatException} if the associated value were passed. This method is intended for use in conjunction with {@link #putFloat}.

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.

param
key key whose associated value is to be returned as a float.
param
def the value to be returned in the event that this preference node has no value associated with key or the associated value cannot be interpreted as a float, or the backing store is inaccessible.
return
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 {@link #removeNode()} method.
throws
NullPointerException if key is null.
see
#putFloat(String,float)
see
#get(String,String)

public abstract intgetInt(java.lang.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 {@link Integer#parseInt(String)}. Returns the specified default if there is no value associated with the key, the backing store is inaccessible, or if Integer.parseInt(String) would throw a {@link NumberFormatException} if the associated value were passed. This method is intended for use in conjunction with {@link #putInt}.

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.

param
key key whose associated value is to be returned as an int.
param
def the value to be returned in the event that this preference node has no value associated with key or the associated value cannot be interpreted as an int, or the backing store is inaccessible.
return
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 {@link #removeNode()} method.
throws
NullPointerException if key is null.
see
#putInt(String,int)
see
#get(String,String)

public abstract longgetLong(java.lang.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 {@link Long#parseLong(String)}. Returns the specified default if there is no value associated with the key, the backing store is inaccessible, or if Long.parseLong(String) would throw a {@link NumberFormatException} if the associated value were passed. This method is intended for use in conjunction with {@link #putLong}.

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.

param
key key whose associated value is to be returned as a long.
param
def the value to be returned in the event that this preference node has no value associated with key or the associated value cannot be interpreted as a long, or the backing store is inaccessible.
return
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 {@link #removeNode()} method.
throws
NullPointerException if key is null.
see
#putLong(String,long)
see
#get(String,String)

public static voidimportPreferences(java.io.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 {@link #exportNode(OutputStream)} and {@link #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 {@link #node(String)} and {@link #put(String, String)}.

param
is the input stream from which to read the XML document.
throws
IOException if reading from the specified input stream results in an IOException.
throws
InvalidPreferencesFormatException Data on input stream does not constitute a valid XML document with the mandated document type.
throws
SecurityException If a security manager is present and it denies RuntimePermission("preferences").
see
RuntimePermission

        XmlSupport.importPreferences(is);
    
public abstract booleanisUserNode()
Returns true if this preference node is in the user preference tree, false if it's in the system preference tree.

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

public abstract java.lang.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.

return
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.
throws
IllegalStateException if this node (or an ancestor) has been removed with the {@link #removeNode()} method.

public abstract java.lang.Stringname()
Returns this preference node's name, relative to its parent.

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

public abstract java.util.prefs.Preferencesnode(java.lang.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).

param
pathName the path name of the preference node to return.
return
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).
throws
NullPointerException if path name is null.
throws
IllegalStateException if this node (or an ancestor) has been removed with the {@link #removeNode()} method.
see
#flush()

public abstract booleannodeExists(java.lang.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 {@link #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.

param
pathName the path name of the node whose existence is to be checked.
return
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.
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).
throws
NullPointerException if path name is null.
throws
IllegalStateException if this node (or an ancestor) has been removed with the {@link #removeNode()} method and pathName is not the empty string ("").

private static java.lang.StringnodeName(java.lang.Class c)
Returns the absolute path name of the node corresponding to the package of the specified object.

throws
IllegalArgumentException if the package has node preferences node associated with it.

        if (c.isArray())
            throw new IllegalArgumentException(
                "Arrays have no associated preferences node.");
        String className = c.getName();
        int pkgEndIndex = className.lastIndexOf('.");
        if (pkgEndIndex < 0)
            return "/<unnamed>";
        String packageName = className.substring(0, pkgEndIndex);
        return "/" + packageName.replace('.", '/");
    
public abstract java.util.prefs.Preferencesparent()
Returns the parent of this preference node, or null if this is the root.

return
the parent of this preference node.
throws
IllegalStateException if this node (or an ancestor) has been removed with the {@link #removeNode()} method.

public abstract voidput(java.lang.String key, java.lang.String value)
Associates the specified value with the specified key in this preference node.

param
key key with which the specified value is to be associated.
param
value value to be associated with the specified key.
throws
NullPointerException if key or value is null.
throws
IllegalArgumentException if key.length() exceeds MAX_KEY_LENGTH or if value.length exceeds MAX_VALUE_LENGTH.
throws
IllegalStateException if this node (or an ancestor) has been removed with the {@link #removeNode()} method.

public abstract voidputBoolean(java.lang.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 {@link #getBoolean}.

param
key key with which the string form of value is to be associated.
param
value value whose string form is to be associated with key.
throws
NullPointerException if key is null.
throws
IllegalArgumentException if key.length() exceeds MAX_KEY_LENGTH.
throws
IllegalStateException if this node (or an ancestor) has been removed with the {@link #removeNode()} method.
see
#getBoolean(String,boolean)
see
#get(String,String)

public abstract voidputByteArray(java.lang.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 {@link #getByteArray}.

param
key key with which the string form of value is to be associated.
param
value value whose string form is to be associated with key.
throws
NullPointerException if key or value is null.
throws
IllegalArgumentException if key.length() exceeds MAX_KEY_LENGTH or if value.length exceeds MAX_VALUE_LENGTH*3/4.
throws
IllegalStateException if this node (or an ancestor) has been removed with the {@link #removeNode()} method.
see
#getByteArray(String,byte[])
see
#get(String,String)

public abstract voidputDouble(java.lang.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 {@link Double#toString(double)}. This method is intended for use in conjunction with {@link #getDouble}.

param
key key with which the string form of value is to be associated.
param
value value whose string form is to be associated with key.
throws
NullPointerException if key is null.
throws
IllegalArgumentException if key.length() exceeds MAX_KEY_LENGTH.
throws
IllegalStateException if this node (or an ancestor) has been removed with the {@link #removeNode()} method.
see
#getDouble(String,double)

public abstract voidputFloat(java.lang.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 {@link Float#toString(float)}. This method is intended for use in conjunction with {@link #getFloat}.

param
key key with which the string form of value is to be associated.
param
value value whose string form is to be associated with key.
throws
NullPointerException if key is null.
throws
IllegalArgumentException if key.length() exceeds MAX_KEY_LENGTH.
throws
IllegalStateException if this node (or an ancestor) has been removed with the {@link #removeNode()} method.
see
#getFloat(String,float)

public abstract voidputInt(java.lang.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 {@link Integer#toString(int)}. This method is intended for use in conjunction with {@link #getInt}.

param
key key with which the string form of value is to be associated.
param
value value whose string form is to be associated with key.
throws
NullPointerException if key is null.
throws
IllegalArgumentException if key.length() exceeds MAX_KEY_LENGTH.
throws
IllegalStateException if this node (or an ancestor) has been removed with the {@link #removeNode()} method.
see
#getInt(String,int)

public abstract voidputLong(java.lang.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 {@link Long#toString(long)}. This method is intended for use in conjunction with {@link #getLong}.

param
key key with which the string form of value is to be associated.
param
value value whose string form is to be associated with key.
throws
NullPointerException if key is null.
throws
IllegalArgumentException if key.length() exceeds MAX_KEY_LENGTH.
throws
IllegalStateException if this node (or an ancestor) has been removed with the {@link #removeNode()} method.
see
#getLong(String,long)

public abstract voidremove(java.lang.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.

param
key key whose mapping is to be removed from the preference node.
throws
NullPointerException if key is null.
throws
IllegalStateException if this node (or an ancestor) has been removed with the {@link #removeNode()} method.

public abstract voidremoveNode()
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 {@link #name()}, {@link #absolutePath()}, {@link #isUserNode()}, {@link #flush()} or {@link #node(String) nodeExists("")} on the corresponding Preferences instance will fail with an IllegalStateException. (The methods defined on {@link 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.
throws
IllegalStateException if this node (or an ancestor) has already been removed with the {@link #removeNode()} method.
throws
UnsupportedOperationException if this method is invoked on the root node.
see
#flush()

public abstract voidremoveNodeChangeListener(java.util.prefs.NodeChangeListener ncl)
Removes the specified NodeChangeListener, so it no longer receives change events.

param
ncl The NodeChangeListener to remove.
throws
IllegalArgumentException if ncl was not a registered NodeChangeListener on this node.
throws
IllegalStateException if this node (or an ancestor) has been removed with the {@link #removeNode()} method.
see
#addNodeChangeListener(NodeChangeListener)

public abstract voidremovePreferenceChangeListener(java.util.prefs.PreferenceChangeListener pcl)
Removes the specified preference change listener, so it no longer receives preference change events.

param
pcl The preference change listener to remove.
throws
IllegalArgumentException if pcl was not a registered preference change listener on this node.
throws
IllegalStateException if this node (or an ancestor) has been removed with the {@link #removeNode()} method.
see
#addPreferenceChangeListener(PreferenceChangeListener)

public abstract voidsync()
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.
throws
IllegalStateException if this node (or an ancestor) has been removed with the {@link #removeNode()} method.
see
#flush()

public static java.util.prefs.PreferencessystemNodeForPackage(java.lang.Class c)
Returns the preference node from the system preference tree that is associated (by convention) with the specified class's package. The convention is as follows: the absolute path name of the node is the fully qualified package name, preceded by a slash ('/'), and with each period ('.') replaced by a slash. For example the absolute path name of the node associated with the class com.acme.widget.Foo 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).

param
c the class for whose package a system preference node is desired.
return
the system preference node associated with the package of which c is a member.
throws
NullPointerException if c is null.
throws
SecurityException if a security manager is present and it denies RuntimePermission("preferences").
see
RuntimePermission

        return systemRoot().node(nodeName(c));
    
public static java.util.prefs.PreferencessystemRoot()
Returns the root preference node for the system.

return
the root preference node for the system.
throws
SecurityException If a security manager is present and it denies RuntimePermission("preferences").
see
RuntimePermission

	SecurityManager security = System.getSecurityManager();
	if (security != null)
            security.checkPermission(prefsPerm);

        return factory.systemRoot();
    
public abstract java.lang.StringtoString()
Returns a string representation of this preferences node, as if computed by the expression:(this.isUserNode() ? "User" : "System") + " Preference Node: " + this.absolutePath().

public static java.util.prefs.PreferencesuserNodeForPackage(java.lang.Class c)
Returns the preference node from the calling user's preference tree that is associated (by convention) with the specified class's package. The convention is as follows: the absolute path name of the node is the fully qualified package name, preceded by a slash ('/'), and with each period ('.') replaced by a slash. For example the absolute path name of the node associated with the class com.acme.widget.Foo 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).

param
c the class for whose package a user preference node is desired.
return
the user preference node associated with the package of which c is a member.
throws
NullPointerException if c is null.
throws
SecurityException if a security manager is present and it denies RuntimePermission("preferences").
see
RuntimePermission


                                                                                                                                                                                                                                                                                                                                                        
         
        return userRoot().node(nodeName(c));
    
public static java.util.prefs.PreferencesuserRoot()
Returns the root preference node for the calling user.

return
the root preference node for the calling user.
throws
SecurityException If a security manager is present and it denies RuntimePermission("preferences").
see
RuntimePermission


                                                    
        
	SecurityManager security = System.getSecurityManager();
	if (security != null)
            security.checkPermission(prefsPerm);

        return factory.userRoot();