abstractpreferences.java

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        try {
            String value = get(key, null);
            if (value != null)
                result = Double.parseDouble(value);
        } catch (NumberFormatException e) {
            // Ignoring exception causes specified default to be returned
        }

        return result;
    }

    /**
     * Implements the <tt>putByteArray</tt> method as per the specification in
     * {@link Preferences#putByteArray(String,byte[])}.
     *
     * @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 <tt>null</tt>.
     * @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.
     */
    public void putByteArray(String key, byte[] value) {
        put(key, Base64.byteArrayToBase64(value));
    }

    /**
     * Implements the <tt>getByteArray</tt> method as per the specification in
     * {@link Preferences#getByteArray(String,byte[])}.
     *
     * @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 <tt>key</tt>
     *        or the associated value cannot be interpreted as a byte array.
     * @return the byte array value represented by the string associated with
     *         <tt>key</tt> in this preference node, or <tt>def</tt> 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 <tt>key</tt> is <tt>null</tt>.  (A 
     *         <tt>null</tt> value for <tt>def</tt> <i>is</i> permitted.)
     */
    public byte[] getByteArray(String key, byte[] def) {
        byte[] result = def;
        String value = get(key, null);
        try {
            if (value != null)
                result = Base64.base64ToByteArray(value);
        }
        catch (RuntimeException e) {
            // Ignoring exception causes specified default to be returned
        }

        return result;
    }

    /**
     * Implements the <tt>keys</tt> method as per the specification in
     * {@link Preferences#keys()}.
     *
     * <p>This implementation obtains this preference node's lock, checks that
     * the node has not been removed and invokes {@link #keysSpi()}.
     *
     * @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 String[] keys() throws BackingStoreException {
        synchronized(lock) {
            if (removed)
                throw new IllegalStateException("Node has been removed.");

            return keysSpi();
        }
    }

    /**
     * Implements the <tt>children</tt> method as per the specification in
     * {@link Preferences#childrenNames()}.
     *
     * <p>This implementation obtains this preference node's lock, checks that
     * the node has not been removed, constructs a <tt>TreeSet</tt> initialized
     * to the names of children already cached (the children in this node's
     * "child-cache"), invokes {@link #childrenNamesSpi()}, and adds all of the
     * returned child-names into the set.  The elements of the tree set are
     * dumped into a <tt>String</tt> array using the <tt>toArray</tt> method,
     * and this array is returned.
     *
     * @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.
     * @see #cachedChildren()
     */
    public String[] childrenNames() throws BackingStoreException {
        synchronized(lock) {
            if (removed)
                throw new IllegalStateException("Node has been removed.");

            Set s = new TreeSet(kidCache.keySet());
            String[] kids = childrenNamesSpi();
            for(int i=0; i<kids.length; i++)
                s.add(kids[i]);
            return (String[]) s.toArray(EMPTY_STRING_ARRAY);
        }
    }

    private static final String[] EMPTY_STRING_ARRAY = new String[0];

    /**
     * Returns all known unremoved children of this node.
     *
     * @return all known unremoved children of this node.
     */
    protected final AbstractPreferences[] cachedChildren() {
        return (AbstractPreferences[]) kidCache.values().
            toArray(EMPTY_ABSTRACT_PREFS_ARRAY);
    }

    private static final AbstractPreferences[] EMPTY_ABSTRACT_PREFS_ARRAY
        = new AbstractPreferences[0];

    /**
     * Implements the <tt>parent</tt> method as per the specification in
     * {@link Preferences#parent()}.
     *
     * <p>This implementation obtains this preference node's lock, checks that
     * the node has not been removed and returns the parent value that was
     * passed to this node's constructor.
     *
     * @return the parent of this preference node.
     * @throws IllegalStateException if this node (or an ancestor) has been
     *         removed with the {@link #removeNode()} method.
     */
    public Preferences parent() {
        synchronized(lock) {
            if (removed)
                throw new IllegalStateException("Node has been removed.");

            return parent;
        }
    }

    /**
     * Implements the <tt>node</tt> method as per the specification in
     * {@link Preferences#node(String)}.
     *
     * <p>This implementation obtains this preference node's lock and checks
     * that the node has not been removed.  If <tt>path</tt> is <tt>""</tt>,
     * this node is returned; if <tt>path</tt> is <tt>"/"</tt>, this node's
     * root is returned.  If the first character in <tt>path</tt> is 
     * not <tt>'/'</tt>, the implementation breaks <tt>path</tt> into
     * tokens and recursively traverses the path from this node to the
     * named node, "consuming" a name and a slash from <tt>path</tt> at
     * each step of the traversal.  At each step, the current node is locked
     * and the node's child-cache is checked for the named node.  If it is
     * not found, the name is checked to make sure its length does not
     * exceed <tt>MAX_NAME_LENGTH</tt>.  Then the {@link #childSpi(String)}
     * method is invoked, and the result stored in this node's child-cache.
     * If the newly created <tt>Preferences</tt> object's {@link #newNode}
     * field is <tt>true</tt> and there are any node change listeners,
     * a notification event is enqueued for processing by the event dispatch
     * thread. 
     *
     * <p>When there are no more tokens, the last value found in the
     * child-cache or returned by <tt>childSpi</tt> is returned by this
     * method.  If during the traversal, two <tt>"/"</tt> tokens occur
     * consecutively, or the final token is <tt>"/"</tt> (rather than a name),
     * an appropriate <tt>IllegalArgumentException</tt> is thrown.
     *
     * <p> If the first character of <tt>path</tt> is <tt>'/'</tt>
     * (indicating an absolute path name name) this preference node's
     * lock is dropped prior to breaking <tt>path</tt> into tokens, and 
     * this method recursively traverses the path starting from the root
     * (rather than starting from this node).  The traversal is otherwise
     * identical to the one described for relative path names.  Dropping
     * the lock on this node prior to commencing the traversal at the root
     * node is essential to avoid the possibility of deadlock, as per the
     * {@link #lock locking invariant}.
     *
     * @param path 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 IllegalStateException if this node (or an ancestor) has been
     *         removed with the {@link #removeNode()} method.
     */
    public Preferences node(String path) {
        synchronized(lock) {
            if (removed)
                throw new IllegalStateException("Node has been removed.");
            if (path.equals(""))
                return this;
            if (path.equals("/"))
                return root;
            if (path.charAt(0) != '/')
                return node(new StringTokenizer(path, "/", true));
        }

        // Absolute path.  Note that we've dropped our lock to avoid deadlock
        return root.node(new StringTokenizer(path.substring(1), "/", true));
    }

    /**
     * tokenizer contains <name> {'/' <name>}*
     */
    private Preferences node(StringTokenizer path) {
        String token = path.nextToken();
        if (token.equals("/"))  // Check for consecutive slashes
            throw new IllegalArgumentException("Consecutive slashes in path");
        synchronized(lock) {
            AbstractPreferences child=(AbstractPreferences)kidCache.get(token);
            if (child == null) {
                if (token.length() > MAX_NAME_LENGTH)
                    throw new IllegalArgumentException(
                        "Node name " + token + " too long");
                child = childSpi(token);
                if (child.newNode)
                    enqueueNodeAddedEvent(child);
                kidCache.put(token, child);
            }
            if (!path.hasMoreTokens())
                return child;
            path.nextToken();  // Consume slash
            if (!path.hasMoreTokens())
                throw new IllegalArgumentException("Path ends with slash");
            return child.node(path);
        }
    }

    /**
     * Implements the <tt>nodeExists</tt> method as per the specification in
     * {@link Preferences#nodeExists(String)}.
     *
     * <p>This implementation is very similar to {@link #node(String)},
     * except that {@link #getChild(String)} is used instead of {@link
     * #childSpi(String)}.
     *
     * @param path 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 IllegalStateException if this node (or an ancestor) has been
     *         removed with the {@link #removeNode()} method and
     *         <tt>pathname</tt> is not the empty string (<tt>""</tt>).
     */
    public boolean nodeExists(String path)
        throws BackingStoreException
    {
        synchronized(lock) {
            if (path.equals(""))
                return !removed;
            if (removed)
                throw new IllegalStateException("Node has been removed.");
            if (path.equals("/"))
                return true;
            if (path.charAt(0) != '/')
                return nodeExists(new StringTokenizer(path, "/", true));
        }

        // Absolute path.  Note that we've dropped our lock to avoid deadlock
        return root.nodeExists(new StringTokenizer(path.substring(1), "/",
                                                   true));
    }

    /**
     * tokenizer contains <name> {'/' <name>}*
     */
    private boolean nodeExists(StringTokenizer path)
        throws BackingStoreException
    {
        String token = path.nextToken();
        if (token.equals("/"))  // Check for consecutive slashes
            throw new IllegalArgumentException("Consecutive slashes in path");
        synchronized(lock) {
            AbstractPreferences child=(AbstractPreferences)kidCache.get(token);
            if (child == null)
                child = getChild(token);
            if (child==null)
                return false;
            if (!path.hasMoreTokens())
                return true;