Package java.util.prefs

Class Preferences

java.lang.Object
java.util.prefs.Preferences
Direct Known Subclasses:
AbstractPreferences
public abstract class Preferences
extends Object
An instance of the class Preferences represents one node in a preference tree, which provides a mechanism to store and access configuration data in a hierarchical way. Two hierarchy trees are maintained, one for system preferences shared by all users and the other for user preferences specific to the user. Preferences hierarchy trees and data are stored in an implementation-dependent back-end.

Every node has one name and one unique absolute path following the same notational conventions as directories in a file system. The root node's name is "", and other node name strings cannot contain the slash character and cannot be empty. The root node's absolute path is "/", and all other nodes' absolute paths are constructed in the standard way: <parent's absolute path> + "/" + <node's name>. Since the set of nodes forms a tree with the root node at its base, all absolute paths start with the slash character. Every node has one relative path to each of its ancestors. The relative path doesn't start with slash: it equals the node's absolute path with leading substring removed corresponding to the ancestor's absolute path and a slash.

Modification to preferences data may be asynchronous, which means that preference update method calls may return immediately instead of blocking. The flush() and sync() methods force the back-end to synchronously perform all pending updates, but the implementation is permitted to perform the modifications on the underlying back-end data at any time between the moment the request is made and the moment the flush() or sync() method returns. Please note that if the JVM exits normally, the implementation must assure all modifications are persisted implicitly.

When invoking a method that retrieves preferences, the user must provide a default value. The default value is returned when the preferences cannot be found or the back-end is unavailable. Some other methods will throw BackingStoreException when the back-end is unavailable.

Preferences can be exported to and imported from an XML files. These documents must have an XML DOCTYPE declaration: 


 <!DOCTYPE preferences SYSTEM "http://java.sun.com/dtd/preferences.dtd">
This system URI is not really accessed by network, it is only a identification string. Visit the DTD location to see the actual format permitted.

There must be a concrete PreferencesFactory type for every concrete Preferences type developed. Every J2SE implementation must provide a default implementation for every supported platform, and must also provide a means of replacing the default implementation. This implementation uses the system property java.util.prefs.PreferencesFactory to determine which preferences implementation to use.

The methods of this class are thread-safe. If multiple JVMs are using the same back-end concurrently, the back-end won't be corrupted, but no other behavior guarantees are made.

Since:
1.4
See Also:
PreferencesFactory

  • Field Summary

    Fields
    Modifier and Type Field Description
    static int MAX_KEY_LENGTH
    Maximum size in characters allowed for a preferences key.
    static int MAX_NAME_LENGTH
    Maximum size in characters allowed for a preferences name.
    static int MAX_VALUE_LENGTH
    Maximum size in characters allowed for a preferences value.

  • Constructor Summary

    Constructors
    Modifier Constructor Description
    protected Preferences()
    Default constructor, for use by subclasses only.

  • Method Summary

    Modifier and Type Method Description
    abstract String absolutePath()
    Gets the absolute path string of this preference node.
    abstract void addNodeChangeListener​(NodeChangeListener ncl)
    Registers a NodeChangeListener instance for this node, which will handle NodeChangeEvents.
    abstract void addPreferenceChangeListener​(PreferenceChangeListener pcl)
    Registers a PreferenceChangeListener instance for this node, which will handle PreferenceChangeEvents.
    abstract String[] childrenNames()
    Returns the names of all children of this node or an empty array if this node has no children.
    abstract void clear()
    Removes all preferences of this node.
    abstract void exportNode​(OutputStream ostream)
    Exports all of the preferences of this node to a XML document using the given output stream.
    abstract void exportSubtree​(OutputStream ostream)
    Exports all of the preferences of this node and all its descendants to a XML document using the given output stream.
    abstract void flush()
    Forces all pending updates to this node and its descendants to be persisted in the backing store.
    abstract String get​(String key, String deflt)
    Gets the String value mapped to the given key or its default value if no value is mapped or no backing store is available.
    abstract boolean getBoolean​(String key, boolean deflt)
    Gets the boolean value mapped to the given key or its default value if no value is mapped, if the backing store is unavailable, or if the value is invalid.
    abstract byte[] getByteArray​(String key, byte[] deflt)
    Gets the byte array value mapped to the given key or its default value if no value is mapped, if the backing store is unavailable, or if the value is an invalid string.
    abstract double getDouble​(String key, double deflt)
    Gets the double value mapped to the given key or its default value if no value is mapped, if the backing store is unavailable, or if the value is an invalid string.
    abstract float getFloat​(String key, float deflt)
    Gets the float value mapped to the given key or its default value if no value is mapped, if the backing store is unavailable, or if the value is an invalid string.
    abstract int getInt​(String key, int deflt)
    Gets the int value mapped to the given key or its default value if no value is mapped, if the backing store is unavailable, or if the value is an invalid string.
    abstract long getLong​(String key, long deflt)
    Gets the long value mapped to the given key or its default value if no value is mapped, if the backing store is unavailable, or if the value is an invalid string.
    static void importPreferences​(InputStream istream)
    Imports all the preferences from an XML document using the given input stream.
    abstract boolean isUserNode()
    Returns whether this is a user preference node.
    abstract String[] keys()
    Returns all preference keys stored in this node or an empty array if no key was found.
    abstract String name()
    Returns the name of this node.
    abstract Preferences node​(String path)
    Returns the preference node with the given path name.
    abstract boolean nodeExists​(String path)
    Returns whether the preference node with the given path name exists.
    abstract Preferences parent()
    Returns the parent preference node of this node or null if this node is the root node.
    abstract void put​(String key, String value)
    Adds a new preference to this node using the given key and value or updates the value if a preference with the given key already exists.
    abstract void putBoolean​(String key, boolean value)
    Adds a new preference with a boolean value to this node using the given key and value or updates the value if a preference with the given key already exists.
    abstract void putByteArray​(String key, byte[] value)
    Adds a new preference to this node using the given key and the string form of the given value or updates the value if a preference with the given key already exists.
    abstract void putDouble​(String key, double value)
    Adds a new preference to this node using the given key and double value or updates the value if a preference with the given key already exists.
    abstract void putFloat​(String key, float value)
    Adds a new preference to this node using the given key and float value or updates the value if a preference with the given key already exists.
    abstract void putInt​(String key, int value)
    Adds a new preference to this node using the given key and int value or updates the value if a preference with the given key already exists.
    abstract void putLong​(String key, long value)
    Adds a new preference to this node using the given key and long value or updates the value if a preference with the given key already exists.
    abstract void remove​(String key)
    Removes the preference mapped to the given key from this node.
    abstract void removeNode()
    Removes this preference node with all its descendants.
    abstract void removeNodeChangeListener​(NodeChangeListener ncl)
    Removes the given NodeChangeListener instance from this node.
    abstract void removePreferenceChangeListener​(PreferenceChangeListener pcl)
    Removes the given PreferenceChangeListener instance from this node.
    abstract void sync()
    Synchronizes the data of this preference node and its descendants with the back-end preference store.
    static Preferences systemNodeForPackage​(Class<?> c)
    Returns the system preference node for the package of the given class.
    static Preferences systemRoot()
    Returns the root node of the system preference hierarchy.
    abstract String toString()
    Returns a string representation of this node.
    static Preferences userNodeForPackage​(Class<?> c)
    Returns the user preference node for the package of the given class.
    static Preferences userRoot()
    Returns the root node of the user preference hierarchy.

    Methods inherited from 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 size in characters allowed for a preferences key.
      See Also:
      Constant Field Values

    • MAX_NAME_LENGTH

      public static final int MAX_NAME_LENGTH
      Maximum size in characters allowed for a preferences name.
      See Also:
      Constant Field Values

    • MAX_VALUE_LENGTH

      public static final int MAX_VALUE_LENGTH
      Maximum size in characters allowed for a preferences value.
      See Also:
      Constant Field Values

  • Constructor Details

    • Preferences

      protected Preferences()
      Default constructor, for use by subclasses only.

  • Method Details

    • absolutePath

      public abstract String absolutePath()
      Gets the absolute path string of this preference node.
      Returns:
      the preference node's absolute path string.

    • childrenNames

      public abstract String[] childrenNames() throws BackingStoreException
      Returns the names of all children of this node or an empty array if this node has no children.
      Returns:
      the names of all children of this node.
      Throws:
      BackingStoreException - if backing store is unavailable or causes an operation failure.
      IllegalStateException - if this node has been removed.

    • clear

      public abstract void clear() throws BackingStoreException
      Removes all preferences of this node.
      Throws:
      BackingStoreException - if backing store is unavailable or causes an operation failure.
      IllegalStateException - if this node has been removed.

    • exportNode

      public abstract void exportNode​(OutputStream ostream) throws IOException, BackingStoreException
      Exports all of the preferences of this node to a XML document using the given output stream.

      This XML document uses the UTF-8 encoding and is written according to the DTD in its DOCTYPE declaration, which is the following: 

       <!DOCTYPE preferences SYSTEM "http://java.sun.com/dtd/preferences.dtd">
      Please note that (unlike the methods of this class that don't concern serialization), this call is not thread-safe.

      Parameters:
      ostream - the output stream to write the XML-formatted data to.
      Throws:
      IOException - if an error occurs while exporting.
      BackingStoreException - if the backing store is unavailable or causes an operation failure.
      IllegalStateException - if this node has been removed.

    • exportSubtree

      public abstract void exportSubtree​(OutputStream ostream) throws IOException, BackingStoreException
      Exports all of the preferences of this node and all its descendants to a XML document using the given output stream.

      This XML document uses the UTF-8 encoding and is written according to the DTD in its DOCTYPE declaration, which is the following: 

       <!DOCTYPE preferences SYSTEM "http://java.sun.com/dtd/preferences.dtd">
      Please note that (unlike the methods of this class that don't concern serialization), this call is not thread-safe.

      Parameters:
      ostream - the output stream to write the XML-formatted data to.
      Throws:
      IOException - if an error occurs while exporting.
      BackingStoreException - if the backing store is unavailable or causes an operation failure.
      IllegalStateException - if this node has been removed.

    • flush

      public abstract void flush() throws BackingStoreException
      Forces all pending updates to this node and its descendants to be persisted in the backing store.

      If this node has been removed, the invocation of this method only flushes this node, not its descendants.

      Throws:
      BackingStoreException - if the backing store is unavailable or causes an operation failure.

    • get

      public abstract String get​(String key, String deflt)
      Gets the String value mapped to the given key or its default value if no value is mapped or no backing store is available.

      Some implementations may store default values in backing stores. In this case, if there is no value mapped to the given key, the stored default value is returned.

      Parameters:
      key - the preference key.
      deflt - the default value, which will be returned if no value is mapped to the given key or no backing store is available.
      Returns:
      the preference value mapped to the given key.
      Throws:
      IllegalStateException - if this node has been removed.
      NullPointerException - if the parameter key is null.

    • getBoolean

      public abstract boolean getBoolean​(String key, boolean deflt)
      Gets the boolean value mapped to the given key or its default value if no value is mapped, if the backing store is unavailable, or if the value is invalid.

      The only valid values are the String "true", which represents true and "false", which represents false, ignoring case.

      Some implementations may store default values in backing stores. In this case, if there is no value mapped to the given key, the stored default value is returned.

      Parameters:
      key - the preference key.
      deflt - the default value, which will be returned if no value is mapped to the given key, if the backing store is unavailable, or if the value is invalid.
      Returns:
      the boolean value mapped to the given key.
      Throws:
      IllegalStateException - if this node has been removed.
      NullPointerException - if the parameter key is null.

    • getByteArray

      public abstract byte[] getByteArray​(String key, byte[] deflt)
      Gets the byte array value mapped to the given key or its default value if no value is mapped, if the backing store is unavailable, or if the value is an invalid string.

      To be valid, the value string must be Base64-encoded binary data. The Base64 encoding is as defined in RFC 2045, section 6.8.

      Some implementations may store default values in backing stores. In this case, if there is no value mapped to the given key, the stored default value is returned.

      Parameters:
      key - the preference key.
      deflt - the default value, which will be returned if no value is mapped to the given key, if the backing store is unavailable, or if the value is invalid.
      Returns:
      the byte array value mapped to the given key.
      Throws:
      IllegalStateException - if this node has been removed.
      NullPointerException - if the parameter key is null.

    • getDouble

      public abstract double getDouble​(String key, double deflt)
      Gets the double value mapped to the given key or its default value if no value is mapped, if the backing store is unavailable, or if the value is an invalid string.

      To be valid, the value string must be a string that can be converted to a double by Double.parseDouble(String).

      Some implementations may store default values in backing stores. In this case, if there is no value mapped to the given key, the stored default value is returned.

      Parameters:
      key - the preference key.
      deflt - the default value, which will be returned if no value is mapped to the given key, if the backing store is unavailable, or if the value is invalid.
      Returns:
      the double value mapped to the given key.
      Throws:
      IllegalStateException - if this node has been removed.
      NullPointerException - if the parameter key is null.

    • getFloat

      public abstract float getFloat​(String key, float deflt)
      Gets the float value mapped to the given key or its default value if no value is mapped, if the backing store is unavailable, or if the value is an invalid string.

      To be valid, the value string must be a string that can be converted to a float by Float.parseFloat(String).

      Some implementations may store default values in backing stores. In this case, if there is no value mapped to the given key, the stored default value is returned.

      Parameters:
      key - the preference key.
      deflt - the default value, which will be returned if no value is mapped to the given key, if the backing store is unavailable, or if the value is invalid.
      Returns:
      the float value mapped to the given key.
      Throws:
      IllegalStateException - if this node has been removed.
      NullPointerException - if the parameter key is null.

    • getInt

      public abstract int getInt​(String key, int deflt)
      Gets the int value mapped to the given key or its default value if no value is mapped, if the backing store is unavailable, or if the value is an invalid string.

      To be valid, the value string must be a string that can be converted to an int by Integer.parseInt(String).

      Some implementations may store default values in backing stores. In this case, if there is no value mapped to the given key, the stored default value is returned.

      Parameters:
      key - the preference key.
      deflt - the default value, which will be returned if no value is mapped to the given key, if the backing store is unavailable, or if the value is invalid.
      Returns:
      the integer value mapped to the given key.
      Throws:
      IllegalStateException - if this node has been removed.
      NullPointerException - if the parameter key is null.

    • getLong

      public abstract long getLong​(String key, long deflt)
      Gets the long value mapped to the given key or its default value if no value is mapped, if the backing store is unavailable, or if the value is an invalid string.

      To be valid, the value string must be a string that can be converted to a long by Long.parseLong(String).

      Some implementations may store default values in backing stores. In this case, if there is no value mapped to the given key, the stored default value is returned.

      Parameters:
      key - the preference key.
      deflt - the default value, which will be returned if no value is mapped to the given key, if the backing store is unavailable, or if the value is invalid.
      Returns:
      the long value mapped to the given key.
      Throws:
      IllegalStateException - if this node has been removed.
      NullPointerException - if the parameter key is null.

    • importPreferences

      public static void importPreferences​(InputStream istream) throws InvalidPreferencesFormatException, IOException
      Imports all the preferences from an XML document using the given input stream.

      This XML document uses the UTF-8 encoding and must be written according to the DTD in its DOCTYPE declaration, which must be the following: 

       <!DOCTYPE preferences SYSTEM "http://java.sun.com/dtd/preferences.dtd">
      Please note that (unlike the methods of this class that don't concern serialization), this call is not thread-safe.

      Parameters:
      istream - the input stream to read the data from.
      Throws:
      InvalidPreferencesFormatException - if the data read from the given input stream is not from a valid XML document.
      IOException - if an error occurs while importing.

    • isUserNode

      public abstract boolean isUserNode()
      Returns whether this is a user preference node.
      Returns:
      true, if this is a user preference node, false if this is a system preference node.

    • keys

      public abstract String[] keys() throws BackingStoreException
      Returns all preference keys stored in this node or an empty array if no key was found.
      Returns:
      the list of all preference keys of this node.
      Throws:
      BackingStoreException - if the backing store is unavailable or causes an operation failure.
      IllegalStateException - if this node has been removed.

    • name

      public abstract String name()
      Returns the name of this node.
      Returns:
      the name of this node.

    • node

      public abstract Preferences node​(String path)
      Returns the preference node with the given path name. The path name can be relative or absolute. The requested node and its ancestors will be created if they do not exist.

      The path is treated as relative to this node if it doesn't start with a slash, otherwise it will be treated as an absolute path.

      Parameters:
      path - the path name of the requested preference node.
      Returns:
      the requested preference node.
      Throws:
      IllegalStateException - if this node has been removed.
      IllegalArgumentException - if the path name is invalid.
      NullPointerException - if the given path is null.

    • nodeExists

      public abstract boolean nodeExists​(String path) throws BackingStoreException
      Returns whether the preference node with the given path name exists. The path is treated as relative to this node if it doesn't start with a slash, otherwise it is treated as an absolute path.

      Please note that if this node has been removed, an invocation of this node will throw an IllegalStateException unless the given path is an empty string, which will return false.

      Parameters:
      path - the path name of the preference node to query.
      Returns:
      true, if the queried preference node exists, false otherwise.
      Throws:
      IllegalStateException - if this node has been removed and the path is not an empty string.
      IllegalArgumentException - if the path name is invalid.
      NullPointerException - if the given path is null.
      BackingStoreException - if the backing store is unavailable or causes an operation failure.

    • parent

      public abstract Preferences parent()
      Returns the parent preference node of this node or null if this node is the root node.
      Returns:
      the parent preference node of this node.
      Throws:
      IllegalStateException - if this node has been removed.

    • put

      public abstract void put​(String key, String value)
      Adds a new preference to this node using the given key and value or updates the value if a preference with the given key already exists.
      Parameters:
      key - the preference key to be added or updated.
      value - the preference value for the given key.
      Throws:
      NullPointerException - if the given key or value is null.
      IllegalArgumentException - if the given key's length is bigger than MAX_KEY_LENGTH or the value's length is bigger than MAX_VALUE_LENGTH.
      IllegalStateException - if this node has been removed.

    • putBoolean

      public abstract void putBoolean​(String key, boolean value)
      Adds a new preference with a boolean value to this node using the given key and value or updates the value if a preference with the given key already exists.
      Parameters:
      key - the preference key to be added or updated.
      value - the preference boolean value for the given key.
      Throws:
      NullPointerException - if the given key is null.
      IllegalArgumentException - if the given key's length is bigger than MAX_KEY_LENGTH.
      IllegalStateException - if this node has been removed.

    • putByteArray

      public abstract void putByteArray​(String key, byte[] value)
      Adds a new preference to this node using the given key and the string form of the given value or updates the value if a preference with the given key already exists.

      The string form of the value is the Base64-encoded binary data of the given byte array. The Base64 encoding is as defined in RFC 2045, section 6.8.

      Parameters:
      key - the preference key to be added or updated.
      value - the preference value for the given key.
      Throws:
      NullPointerException - if the given key or value is null.
      IllegalArgumentException - if the given key's length is bigger than MAX_KEY_LENGTH or value's length is bigger than three quarters of MAX_KEY_LENGTH.
      IllegalStateException - if this node has been removed.

    • putDouble

      public abstract void putDouble​(String key, double value)
      Adds a new preference to this node using the given key and double value or updates the value if a preference with the given key already exists.

      The value is stored in its string form, which is the result of invoking Double.toString(double).

      Parameters:
      key - the preference key to be added or updated.
      value - the preference value for the given key.
      Throws:
      NullPointerException - if the given key is null.
      IllegalArgumentException - if the given key's length is bigger than MAX_KEY_LENGTH.
      IllegalStateException - if this node has been removed.

    • putFloat

      public abstract void putFloat​(String key, float value)
      Adds a new preference to this node using the given key and float value or updates the value if a preference with the given key already exists.

      The value is stored in its string form, which is the result of invoking Float.toString(float).

      Parameters:
      key - the preference key to be added or updated.
      value - the preference value for the given key.
      Throws:
      NullPointerException - if the given key is null.
      IllegalArgumentException - if the given key's length is bigger than MAX_KEY_LENGTH.
      IllegalStateException - if this node has been removed.

    • putInt

      public abstract void putInt​(String key, int value)
      Adds a new preference to this node using the given key and int value or updates the value if a preference with the given key already exists.

      The value is stored in its string form, which is the result of invoking Integer.toString(int).

      Parameters:
      key - the preference key to be added or updated.
      value - the preference value for the given key.
      Throws:
      NullPointerException - if the given key is null.
      IllegalArgumentException - if the given key's length is bigger than MAX_KEY_LENGTH.
      IllegalStateException - if this node has been removed.

    • putLong

      public abstract void putLong​(String key, long value)
      Adds a new preference to this node using the given key and long value or updates the value if a preference with the given key already exists.

      The value is stored in its string form, which is the result of invoking Long.toString(long).

      Parameters:
      key - the preference key to be added or updated.
      value - the preference value for the given key.
      Throws:
      NullPointerException - if the given key is null.
      IllegalArgumentException - if the given key's length is bigger than MAX_KEY_LENGTH.
      IllegalStateException - if this node has been removed.

    • remove

      public abstract void remove​(String key)
      Removes the preference mapped to the given key from this node.
      Parameters:
      key - the key of the preference to be removed.
      Throws:
      NullPointerException - if the given key is null.
      IllegalStateException - if this node has been removed.

    • removeNode

      public abstract void removeNode() throws BackingStoreException
      Removes this preference node with all its descendants. The removal won't necessarily be persisted until the method flush() is invoked.
      Throws:
      BackingStoreException - if the backing store is unavailable or causes an operation failure.
      IllegalStateException - if this node has been removed.
      UnsupportedOperationException - if this is a root node.

    • addNodeChangeListener

      public abstract void addNodeChangeListener​(NodeChangeListener ncl)
      Registers a NodeChangeListener instance for this node, which will handle NodeChangeEvents. NodeChangeEvents will be fired when a child node has been added to or removed from this node.
      Parameters:
      ncl - the listener to be registered.
      Throws:
      NullPointerException - if the given listener is null.
      IllegalStateException - if this node has been removed.

    • addPreferenceChangeListener

      public abstract void addPreferenceChangeListener​(PreferenceChangeListener pcl)
      Registers a PreferenceChangeListener instance for this node, which will handle PreferenceChangeEvents. PreferenceChangeEvents will be fired when a preference has been added to, removed from, or updated for this node.
      Parameters:
      pcl - the listener to be registered.
      Throws:
      NullPointerException - if the given listener is null.
      IllegalStateException - if this node has been removed.

    • removeNodeChangeListener

      public abstract void removeNodeChangeListener​(NodeChangeListener ncl)
      Removes the given NodeChangeListener instance from this node.
      Parameters:
      ncl - the listener to be removed.
      Throws:
      IllegalArgumentException - if the given listener is null.
      IllegalStateException - if this node has been removed.

    • removePreferenceChangeListener

      public abstract void removePreferenceChangeListener​(PreferenceChangeListener pcl)
      Removes the given PreferenceChangeListener instance from this node.
      Parameters:
      pcl - the listener to be removed.
      Throws:
      IllegalArgumentException - if the given listener is null.
      IllegalStateException - if this node has been removed.

    • sync

      public abstract void sync() throws BackingStoreException
      Synchronizes the data of this preference node and its descendants with the back-end preference store. Any changes found in the back-end data should be reflected in this node and its descendants, and at the same time any local changes to this node and descendants should be persisted.
      Throws:
      BackingStoreException - if the backing store is unavailable or causes an operation failure.
      IllegalStateException - if this node has been removed.

    • systemNodeForPackage

      public static Preferences systemNodeForPackage​(Class<?> c)
      Returns the system preference node for the package of the given class. The absolute path of the returned node is one slash followed by the given class's full package name, replacing each period character ('.') with a slash. For example, the absolute path of the preference associated with the class Object would be "/java/lang". As a special case, the unnamed package is associated with a preference node "/<unnamed>". This method will create the node and its ancestors as needed. Any nodes created by this method won't necessarily be persisted until the method flush() is invoked.
      Parameters:
      c - the given class.
      Returns:
      the system preference node for the package of the given class.
      Throws:
      NullPointerException - if the given class is null.

    • systemRoot

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

    • userNodeForPackage

      public static Preferences userNodeForPackage​(Class<?> c)
      Returns the user preference node for the package of the given class. The absolute path of the returned node is one slash followed by the given class's full package name, replacing each period character ('.') with a slash. For example, the absolute path of the preference associated with the class Object would be "/java/lang". As a special case, the unnamed package is associated with a preference node "/<unnamed>". This method will create the node and its ancestors as needed. Any nodes created by this method won't necessarily be persisted until the method flush() is invoked.
      Parameters:
      c - the given class.
      Returns:
      the user preference node for the package of the given class.
      Throws:
      NullPointerException - if the given class is null.

    • userRoot

      public static Preferences userRoot()
      Returns the root node of the user preference hierarchy.
      Returns:
      the user preference hierarchy root node.

    • toString

      public abstract String toString()
      Returns a string representation of this node. The format is "User/System Preference Node: " followed by this node's absolute path.
      Overrides:
      toString in class Object
      Returns:
      the string representation of this node.