Visual Cafe 3/Visual Cafe 3.ISO/Vcafe/JFC.bin/AbstractDocument.java

Text File | 1998-06-30 | 62KB | 2,065 lines

/*
 * @(#)AbstractDocument.java    1.77 98/04/09
 *
 * Copyright (c) 1997 Sun Microsystems, Inc. All Rights Reserved.
 *
 * This software is the confidential and proprietary information of Sun
 * Microsystems, Inc. ("Confidential Information").  You shall not
 * disclose such Confidential Information and shall use it only in
 * accordance with the terms of the license agreement you entered into
 * with Sun.
 *
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
 * SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 * PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES
 * SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING
 * THIS SOFTWARE OR ITS DERIVATIVES.
 *
 */
package com.sun.java.swing.text;

import java.util.*;
import java.io.*;

import com.sun.java.swing.undo.*;
import com.sun.java.swing.event.ChangeListener;
import com.sun.java.swing.event.*;

/**
 * An implementation of the document interface to serve as a
 * basis for implementing various kinds of documents.  At this
 * level there is very little policy, so there is a corresponding
 * increase in difficulty of use.
 * <p>
 * This class implements a locking mechanism for the document.  It
 * allows multiple readers or one writer, and writers must wait until
 * all observers of the document have been notified of a previous
 * change before beginning another mutation to the document.  The
 * read lock is aquired and released using the <code>render</code>
 * method.  A write lock is aquired by the methods that mutate the
 * document, and are held for the duration of the method call.
 * Notification is done on the thread that produced the mutation,
 * and the thread has full read access to the document for the
 * duration of the notification, but other readers are kept out
 * until the notification has finished.  The notification is a
 * beans event notification which does not allow any further
 * mutations until all listeners have been notified.
 * <p>
 * Any models subclassed from this class and used in conjunction
 * with a text component that has a look and feel implementation
 * that is derived from DefaultTextUI may be safely updated
 * asynchronously.  The rendering in DefaultTextUI occurs under
 * the protection of the <code>render</code> method, which makes
 * rendering safe if it is running on the event thread (which
 * happens if using repaint to schedule updates).  The code path
 * for any DocumentListener implementation must not access the
 * component lock if trying to be safe from deadlocks.
 * The <cod>repaint</code> and <code>revalidate</code> methods
 * on JComponent are safe.
 * <p>
 * Warning: serialized objects of this class will not be compatible with
 * future swing releases.  The current serialization support is appropriate
 * for short term storage or RMI between Swing1.0 applications.  It will
 * not be possible to load serialized Swing1.0 objects with future releases
 * of Swing.  The JDK1.2 release of Swing will be the compatibility
 * baseline for the serialized form of Swing objects.
 *
 * @author  Timothy Prinzing
 * @version 1.77 04/09/98
 */
public abstract class AbstractDocument implements Document, Serializable {

    /**
     * Constructs a new AbstractDocument, wrapped around some
     * specified content storage mechanism.
     *
     * @param data the content
     */
    protected AbstractDocument(Content data) {
    this(data, StyleContext.getDefaultStyleContext());
    }

    /**
     * Constructs a new AbstractDocument, wrapped around some
     * specified content storage mechanism.
     *
     * @param data the content
     * @param context the attribute context
     */
    protected AbstractDocument(Content data, AttributeContext context) {
    this.data = data;
    this.context = context;
    }

    /**
     * Support for managing a set of properties. Callers
     * can use the documentProperties dictionary to annotate the
     * document with document-wide properties.
     *
     * @return a non null Dictionary
     * @see #setDocumentProperties
     */
    public Dictionary getDocumentProperties() {
    if (documentProperties == null) {
        documentProperties = new Hashtable(2);
    }
    return documentProperties;
    }

    /**
     * Replace the document properties dictionary for this document.
     *
     * @param x the new dictionary
     * @see #getDocumentProperties
     */
    public void setDocumentProperties(Dictionary x) {
    documentProperties = x;
    }

    /**
     * Notifies all listeners that have registered interest for
     * notification on this event type.  The event instance
     * is lazily created using the parameters passed into
     * the fire method.
     *
     * @param e the event
     * @see EventListenerList
     */
    protected void fireInsertUpdate(DocumentEvent e) {
    // Guaranteed to return a non-null array
    Object[] listeners = listenerList.getListenerList();
    // Process the listeners last to first, notifying
    // those that are interested in this event
    for (int i = listeners.length-2; i>=0; i-=2) {
        if (listeners[i]==DocumentListener.class) {
        // Lazily create the event:
        // if (e == null)
        // e = new ListSelectionEvent(this, firstIndex, lastIndex);
        ((DocumentListener)listeners[i+1]).insertUpdate(e);
        }
    }
    }

    /**
     * Notifies all listeners that have registered interest for
     * notification on this event type.  The event instance
     * is lazily created using the parameters passed into
     * the fire method.
     *
     * @param e the event
     * @see EventListenerList
     */
    protected void fireChangedUpdate(DocumentEvent e) {
    // Guaranteed to return a non-null array
    Object[] listeners = listenerList.getListenerList();
    // Process the listeners last to first, notifying
    // those that are interested in this event
    for (int i = listeners.length-2; i>=0; i-=2) {
        if (listeners[i]==DocumentListener.class) {
        // Lazily create the event:
        // if (e == null)
        // e = new ListSelectionEvent(this, firstIndex, lastIndex);
        ((DocumentListener)listeners[i+1]).changedUpdate(e);
        }
    }
    }

    /**
     * Notifies all listeners that have registered interest for
     * notification on this event type.  The event instance
     * is lazily created using the parameters passed into
     * the fire method.
     *
     * @param e the event
     * @see EventListenerList
     */
    protected void fireRemoveUpdate(DocumentEvent e) {
    // Guaranteed to return a non-null array
    Object[] listeners = listenerList.getListenerList();
    // Process the listeners last to first, notifying
    // those that are interested in this event
    for (int i = listeners.length-2; i>=0; i-=2) {
        if (listeners[i]==DocumentListener.class) {
        // Lazily create the event:
        // if (e == null)
        // e = new ListSelectionEvent(this, firstIndex, lastIndex);
        ((DocumentListener)listeners[i+1]).removeUpdate(e);
        }
    }
    }

    /**
     * Notifies all listeners that have registered interest for
     * notification on this event type.  The event instance
     * is lazily created using the parameters passed into
     * the fire method.
     *
     * @param e the event
     * @see EventListenerList
     */
    protected void fireUndoableEditUpdate(UndoableEditEvent e) {
    // Guaranteed to return a non-null array
    Object[] listeners = listenerList.getListenerList();
    // Process the listeners last to first, notifying
    // those that are interested in this event
    for (int i = listeners.length-2; i>=0; i-=2) {
        if (listeners[i]==UndoableEditListener.class) {
        // Lazily create the event:
        // if (e == null)
        // e = new ListSelectionEvent(this, firstIndex, lastIndex);
        ((UndoableEditListener)listeners[i+1]).undoableEditHappened(e);
        }
    }
    }

    // --- Document methods -----------------------------------------

    /**
     * This allows the model to be safely rendered in the presence
     * of currency, if the model supports being updated asynchronously.
     * The given runnable will be executed in a way that allows it
     * to safely read the model with no changes while the runnable
     * is being executed.  The runnable itself may <em>not</em>
     * make any mutations.
     * <p>
     * This is implemented to aquire a read lock for the duration
     * of the runnables execution.  There may be multiple runnables
     * executing at the same time, and all writers will be blocked
     * while there are active rendering runnables.  If the runnable
     * throws an exception, its lock will be safely released.
     * There is no protection against a runnable that never exits,
     * which will effectively leave the document locked for it's
     * lifetime.
     * <p>
     * If the given runnable attempts to make any mutations in
     * this implementation, a deadlock will occur.  There is
     * no tracking of individual rendering threads to enable
     * detecting this situation, but a subclass could incur
     * the overhead of tracking them and throwing an error.
     * <p>
     * This method is thread safe, although most Swing methods
     * are not. Please see
     * <A HREF="http://java.sun.com/products/jfc/swingdoc-archive/threads.html">Threads
     * and Swing</A> for more information.
     *
     * @param r the renderer to execute.
     */
    public void render(Runnable r) {
    try {
        readLock();
        r.run();
    } finally {
        readUnlock();
    }
    }

    /**
     * Returns the length of the data.  This is the number of
     * characters of content that represents the users data.
     *
     * @return the length >= 0
     * @see Document#getLength
     */
    public int getLength() {
    return data.length() - 1;
    }

    /**
     * Adds a document listener for notification of any changes.
     *
     * @param listener the listener
     * @see Document#addDocumentListener
     */
    public void addDocumentListener(DocumentListener listener) {
    listenerList.add(DocumentListener.class, listener);
    }

    /**
     * Removes a document listener.
     *
     * @param listener the listener
     * @see Document#removeDocumentListener
     */
    public void removeDocumentListener(DocumentListener listener) {
    listenerList.remove(DocumentListener.class, listener);
    }

    /**
     * Adds an undo listener for notification of any changes.
     * Undo/Redo operations performed on the UndoableEdit will
     * cause the appropriate DocumentEvent to be fired to keep
     * the view(s) in sync with the model.
     *
     * @param listener the listener
     * @see Document#addUndoableEditListener
     */
    public void addUndoableEditListener(UndoableEditListener listener) {
    listenerList.add(UndoableEditListener.class, listener);
    }

    /**
     * Removes an undo listener.
     *
     * @param listener the listener
     * @see Document#removeDocumentListener
     */
    public void removeUndoableEditListener(UndoableEditListener listener) {
    listenerList.remove(UndoableEditListener.class, listener);
    }

    /**
     * A convenience method for looking up a property value. It is
     * equivalent to:
     * <pre>
     * getDocumentProperties().get(key);
     * </pre>
     *
     * @param key the non-null property key
     * @return the value of this property or null
     * @see #getDocumentProperties
     */
    public final Object getProperty(Object key) {
        return getDocumentProperties().get(key);
    }


    /**
     * A convenience method for storing up a property value.  It is
     * equivalent to:
     * <pre>
     * getDocumentProperties().put(key, value);
     * </pre>
     * If value is null this method will remove the property
     *
     * @param key the non-null key
     * @param value the value
     * @see #getDocumentProperties
     */
    public final void putProperty(Object key, Object value) {
    if (value != null) {
        getDocumentProperties().put(key, value);
    } else
            getDocumentProperties().remove(key);
    }

    /**
     * Removes some content from the document.
     * Removing content causes a write lock to be held while the
     * actual changes are taking place.  Observers are notified
     * of the change on the thread that called this method.
     * <p>
     * This method is thread safe, although most Swing methods
     * are not. Please see
     * <A HREF="http://java.sun.com/products/jfc/swingdoc-archive/threads.html">Threads
     * and Swing</A> for more information.
     *
     * @param offs the starting offset >= 0
     * @param len the number of characters to remove >= 0
     * @exception BadLocationException  the given remove position is not a valid
     *   position within the document
     * @see Document#remove
     */
    public void remove(int offs, int len) throws BadLocationException {
    if (len > 0) {
        try {
        writeLock();
        DefaultDocumentEvent chng =
            new DefaultDocumentEvent(offs, len, DocumentEvent.EventType.REMOVE);
        removeUpdate(chng);
        UndoableEdit u = data.remove(offs, len);
        if (u != null) {
            chng.addEdit(u);
        }
        // Mark the edit as done.
        chng.end();
        fireRemoveUpdate(chng);
        // only fire undo if Content implementation supports it
        if (u != null) {
            fireUndoableEditUpdate(new UndoableEditEvent(this, chng));
        }
        } finally {
        writeUnlock();
        }
    }
    }

    /**
     * Inserts some content into the document.
     * Inserting content causes a write lock to be held while the
     * actual changes are taking place, followed by notification
     * to the observers on the thread that grabbed the write lock.
     * <p>
     * This method is thread safe, although most Swing methods
     * are not. Please see
     * <A HREF="http://java.sun.com/products/jfc/swingdoc-archive/threads.html">Threads
     * and Swing</A> for more information.
     *
     * @param offs the starting offset >= 0
     * @param str the string to insert; does nothing with null/empty strings
     * @param a the attributes for the inserted content
     * @exception BadLocationException  the given insert position is not a valid
     *   position within the document
     * @see Document#insertString
     */
    public void insertString(int offs, String str, AttributeSet a) throws BadLocationException {
    if ((str == null) || (str.length() == 0)) {
        return;
    }
    try {
        writeLock();
        UndoableEdit u = data.insertString(offs, str);
        DefaultDocumentEvent e =
        new DefaultDocumentEvent(offs, str.length(), DocumentEvent.EventType.INSERT);
        if (u != null) {
        e.addEdit(u);
        }
        insertUpdate(e, a);
        // Mark the edit as done.
        e.end();
        fireInsertUpdate(e);
        // only fire undo if Content implementation supports it
        if (u != null) {
        fireUndoableEditUpdate(new UndoableEditEvent(this, e));
        }
    } finally {
        writeUnlock();
    }
    }

    /**
     * Gets a sequence of text from the document.
     *
     * @param offset the starting offset >= 0
     * @param length the number of characters to retrieve >= 0
     * @return the text
     * @exception BadLocationException  the range given includes a position
     *   that is not a valid position within the document
     * @see Document#getText
     */
    public String getText(int offset, int length) throws BadLocationException {
    String str = data.getString(offset, length);
    return str;
    }

    /**
     * Gets some text from the document potentially without
     * making a copy.  The character array returned in the
     * given <code>Segment</code> should never be mutated.
     * This kind of access to the characters of the document
     * is provided to help make the rendering potentially more
     * efficient.  The caller should make no assumptions about
     * the lifetime of the returned character array, which
     * should be copied if needed beyond the use for rendering.
     *
     * @param offset the starting offset >= 0
     * @param length the number of characters to retrieve >= 0
     * @param txt the Segment object to retrieve the text into
     * @exception BadLocationException  the range given includes a position
     *   that is not a valid position within the document
     */
    public void getText(int offset, int length, Segment txt) throws BadLocationException {
    data.getChars(offset, length, txt);
    }

    /**
     * Returns a position that will track change as the document
     * is altered.
     * <p>
     * This method is thread safe, although most Swing methods
     * are not. Please see
     * <A HREF="http://java.sun.com/products/jfc/swingdoc-archive/threads.html">Threads
     * and Swing</A> for more information.
     *
     * @param offs the position in the model >= 0
     * @return the position
     * @exception BadLocationException  if the given position does not
     *   represent a valid location in the associated document
     * @see Document#createPosition
     */
    public synchronized Position createPosition(int offs) throws BadLocationException {
    return data.createPosition(offs);
    }

    /**
     * Returns a position that represents the start of the document.  The
     * position returned can be counted on to track change and stay
     * located at the beginning of the document.
     *
     * @return the position
     */
    public final Position getStartPosition() {
    Position p;
    try {
        p = createPosition(0);
    } catch (BadLocationException bl) {
        p = null;
    }
    return p;
    }

    /**
     * Returns a position that represents the end of the document.  The
     * position returned can be counted on to track change and stay
     * located at the end of the document.
     *
     * @return the position
     */
    public final Position getEndPosition() {
    Position p;
    try {
        p = createPosition(data.length());
    } catch (BadLocationException bl) {
        p = null;
    }
    return p;
    }

    /**
     * Gets all root elements defined.  Typically, there
     * will only be one so the default implementation
     * is to return the default root element.
     *
     * @return the root element
     */
    public Element[] getRootElements() {
    Element[] elems = new Element[1];
    elems[0] = getDefaultRootElement();
    return elems;
    }

    /**
     * Returns the root element that views should be based upon
     * unless some other mechanism for assigning views to element
     * structures is provided.
     *
     * @return the root element
     * @see Document#getDefaultRootElement
     */
    public abstract Element getDefaultRootElement();

    // ---- local methods -----------------------------------------

    /**
     * Fetches the context for managing attributes.  This
     * method effectively establishes the strategy used
     * for compressing AttributeSet information.
     *
     * @return the context
     */
    protected final AttributeContext getAttributeContext() {
    return context;
    }

    /**
     * Updates document structure as a result of text insertion.  This
     * will happen within a write lock.  If a subclass of
     * this class reimplements this method, it should delegate to the
     * superclass as well.
     *
     * @param chng a description of the change
     * @param attr the attributes for the change
     */
    protected void insertUpdate(DefaultDocumentEvent chng, AttributeSet attr) {
    }

    /**
     * Updates any document structure as a result of text removal.
     * This will happen within a write lock. If a subclass
     * of this class reimplements this method, it should delegate to the
     * superclass as well.
     *
     * @param chng a description of the change
     */
    protected void removeUpdate(DefaultDocumentEvent chng) {
    }

    /**
     * Gives a diagnostic dump.
     *
     * @param out the output stream
     */
    public void dump(PrintStream out) {
    Element root = getDefaultRootElement();
    if (root instanceof AbstractElement) {
        ((AbstractElement)root).dump(out, 0);
    }
    }

    /**
     * Gets the content for the document.
     *
     * @return the content
     */
    protected final Content getContent() {
    return data;
    }

    /**
     * Creates a document leaf element.
     * Hook through which elements are created to represent the
     * document structure.  Because this implementation keeps
     * structure and content seperate, elements grow automatically
     * when content is extended so splits of existing elements
     * follow.  The document itself gets to decide how to generate
     * elements to give flexibility in the type of elements used.
     *
     * @param parent the parent element
     * @param a the attributes for the element
     * @param p0 the beginning of the range >= 0
     * @param p1 the end of the range >= p0
     * @return the new element
     */
    protected Element createLeafElement(Element parent, AttributeSet a, int p0, int p1) {
    return new LeafElement(parent, a, p0, p1);
    }

    /**
     * Creates a document branch element, that can contain other elements.
     *
     * @param parent the parent element
     * @param a the attributes
     * @return the element
     */
    protected Element createBranchElement(Element parent, AttributeSet a) {
    return new BranchElement(parent, a);
    }

    // --- Document locking ----------------------------------

    /**
     * Fetches the current writing thread if there is one.
     * This can be used to distinguish whether a method is
     * being called as part of an existing modification or
     * if a lock needs to be acquired and a new transaction
     * started.
     *
     * @returns the thread actively modifying the document
     *  or null if there are no modifications in progress
     */
    protected synchronized final Thread getCurrentWriter() {
    return currWriter;
    }

    /**
     * Acquires a lock to begin mutating the document this lock
     * protects.  There can be no notification of changes or
     * reading going on in order to gain the lock.
     */
    protected synchronized final void writeLock() {
    try {
        while ((numReaders > 0) || (currWriter != null)) {
        wait();
        }
        currWriter = Thread.currentThread();
    } catch (InterruptedException e) {
        // safe to let this pass... write lock not
        // held if the thread lands here.
    }
    }

    /**
     * Releases the write lock held because the write
     * operation is finished.  This allows either a new
     * writer or readers to aquire a lock.
     */
    protected synchronized final void writeUnlock() {
    if ((numReaders > 0) || (currWriter == null)) {
        throw new StateInvariantError(BAD_LOCK_STATE);
    }
    currWriter = null;
    notify();
    }

    /**
     * Acquires a lock to begin reading some state from the
     * document.  There can be multiple readers at the same time
     * and reading can occur while notification to the listeners
     * is going on, but writing blocks the readers.
     */
    protected synchronized final void readLock() {
    try {
        while (currWriter != null) {
        wait();
        }
        numReaders += 1;
    } catch (InterruptedException e) {
        // safe to let this pass... read lock not
        // held if the thread lands here.
    }
    }

    /**
     * Does a read unlock.
     * One of the readers is done.  If there are no more readers
     * then writing can begin again.
     */
    protected synchronized final void readUnlock() {
    if (numReaders <= 0) {
        throw new StateInvariantError(BAD_LOCK_STATE);
    }
    numReaders -= 1;
    notify();
    }

    // --- serialization ---------------------------------------------

    private void readObject(ObjectInputStream s)
      throws ClassNotFoundException, IOException
    {
    s.defaultReadObject();
    listenerList = new EventListenerList();
    }

    // ----- member variables ------------------------------------------

    private transient int numReaders;
    private transient Thread currWriter;

    /**
     * Storage for document-wide properties.
     */
    private Dictionary documentProperties = null;

    /**
     * The event listener list for the document.
     */
    protected EventListenerList listenerList = new EventListenerList();

    /**
     * Where the text is actually stored, and a set of marks
     * that track change as the document is edited are managed.
     */
    private Content data;

    /**
     * Factory for the attributes.  This is the strategy for
     * attribute compression and control of the lifetime of
     * a set of attributes as a collection.  This may be shared
     * with other documents.
     */
    private AttributeContext context;

    private static final String BAD_LOCK_STATE = "document lock failure";

    /**
     * Error message to indicate a bad location.
     */
    protected static final String BAD_LOCATION = "document location failure";

    /**
     * Name of elements used to represent paragraphs
     */
    public static final String ParagraphElementName = "paragraph";

    /**
     * Name of elements used to represent content
     */
    public static final String ContentElementName = "content";

    /**
     * Name of elements used to hold sections (lines/paragraphs).
     */
    public static final String SectionElementName = "section";

    /**
     * Name of the attribute used to specify element
     * names.
     */
    public static final String ElementNameAttribute = "$ename";

    /**
     * Interface to describe a sequence of character content that
     * can be edited.  Implementations may or may not support a
     * history mechanism which will be reflected by whether or not
     * mutations return an UndoableEdit implementation.
     * @see AbstractDocument
     */
    public interface Content {

    /**
     * Creates a position within the content that will
     * track change as the content is mutated.
         *
         * @param offset the offset in the content >= 0
         * @return a Position
         * @exception BadLocationException for an invalid offset
     */
    public Position createPosition(int offset) throws BadLocationException;

    /**
     * Current length of the sequence of character content.
         *
         * @return the length >= 0
     */
        public int length();

    /**
     * Inserts a string of characters into the sequence.
     *
     * @param where   Offset into the sequence to make the insertion >= 0.
     * @param str     String to insert.
     * @return  If the implementation supports a history mechansim,
     *    a reference to an Edit implementation will be returned,
     *    otherwise null.
     * @exception BadLocationException  Thrown if the area covered by
     *   the arguments is not contained in the character sequence.
     */
        public UndoableEdit insertString(int where, String str) throws BadLocationException;

    /**
     * Removes some portion of the sequence.
     *
     * @param where   The offset into the sequence to make the
         *   insertion >= 0.
     * @param nitems  The number of items in the sequence to remove >= 0.
     * @return  If the implementation supports a history mechansim,
     *    a reference to an Edit implementation will be returned,
     *    otherwise null.
     * @exception BadLocationException  Thrown if the area covered by
     *   the arguments is not contained in the character sequence.
     */
        public UndoableEdit remove(int where, int nitems) throws BadLocationException;

    /**
     * Fetches a string of characters contained in the sequence.
     *
     * @param where   Offset into the sequence to fetch >= 0.
     * @param len     number of characters to copy >= 0.
         * @return the string
     * @exception BadLocationException  Thrown if the area covered by
     *   the arguments is not contained in the character sequence.
     */
        public String getString(int where, int len) throws BadLocationException;

        /**
         * Gets a sequence of characters and copies them into a Segment.
         *
         * @param where the starting offset >= 0
         * @param len the number of characters >= 0
         * @param txt the target location to copy into
     * @exception BadLocationException  Thrown if the area covered by
     *   the arguments is not contained in the character sequence.
         */
        public void getChars(int where, int len, Segment txt) throws BadLocationException;
    }

    /**
     * An interface that can be used to allow MutableAttributeSet
     * implementations to use pluggable attribute compression
     * techniques.  Each mutation of the attribute set can be
     * used to exchange a previous AttributeSet instance with
     * another, preserving the possibility of the AttributeSet
     * remaining immutable.  An implementation is provided by
     * the StyleContext class.
     *
     * The Element implementations provided by this class use
     * this interface to provide their MutableAttributeSet
     * implementations, so that different AttributeSet compression
     * techniques can be employed.  The method
     * <code>getAttributeContext</code> should be implemented to
     * return the object responsible for implementing the desired
     * compression technique.
     *
     * @see StyleContext
     */
    public interface AttributeContext {

    /**
     * Adds an attribute to the given set, and returns
     * the new representative set.
     *
         * @param old the old attribute set
     * @param name the non-null attribute name
     * @param value the attribute value
         * @return the updated attribute set
     * @see MutableAttributeSet#addAttribute
     */
        public AttributeSet addAttribute(AttributeSet old, Object name, Object value);

    /**
     * Adds a set of attributes to the element.
     *
         * @param old the old attribute set
     * @param attr the attributes to add
         * @return the updated attribute set
     * @see MutableAttributeSet#addAttribute
     */
        public AttributeSet addAttributes(AttributeSet old, AttributeSet attr);

    /**
     * Removes an attribute from the set.
     *
         * @param old the old attribute set
     * @param name the non-null attribute name
         * @return the updated attribute set
     * @see MutableAttributeSet#removeAttribute
     */
        public AttributeSet removeAttribute(AttributeSet old, Object name);

    /**
     * Removes a set of attributes for the element.
     *
         * @param old the old attribute set
     * @param names the attribute names
         * @return the updated attribute set
     * @see MutableAttributeSet#removeAttributes
     */
        public AttributeSet removeAttributes(AttributeSet old, Enumeration names);

    /**
     * Removes a set of attributes for the element.
     *
         * @param old the old attribute set
     * @param attrs the attributes
         * @return the updated attribute set
     * @see MutableAttributeSet#removeAttributes
     */
        public AttributeSet removeAttributes(AttributeSet old, AttributeSet attrs);

    /**
     * Fetches an empty AttributeSet.
         *
         * @return the attribute set
     */
    public AttributeSet getEmptySet();

    /**
         * Reclaims an attribute set.
     * This is a way for a MutableAttributeSet to mark that it no
     * longer need a particular immutable set.  This is only necessary
     * in 1.1 where there are no weak references.  A 1.1 implementation
     * would call this in its finalize method.
         *
         * @param a the attribute set to reclaim
     */
    public void reclaim(AttributeSet a);
    }

    /**
     * Implements the abstract part of an element.  By default elements
     * support attributes by having a field that represents the immutable
     * part of the current attribute set for the element.  The element itself
     * implements MutableAttributeSet which can be used to modify the set
     * by fetching a new immutable set.  The immutable sets are provided
     * by the AttributeContext associated with the document.
     * <p>
     * Warning: serialized objects of this class will not be compatible with
     * future swing releases.  The current serialization support is appropriate
     * for short term storage or RMI between Swing1.0 applications.  It will
     * not be possible to load serialized Swing1.0 objects with future releases
     * of Swing.  The JDK1.2 release of Swing will be the compatibility
     * baseline for the serialized form of Swing objects.
     */
    public abstract class AbstractElement implements Element, MutableAttributeSet, Serializable {

        /**
         * Creates a new AbstractElement.
         *
         * @param parent the parent element
         * @param a the attributes for the element
         */
        public AbstractElement(Element parent, AttributeSet a) {
        attributes = (a != null) ? a.copyAttributes() :
        getAttributeContext().getEmptySet();
        this.parent = parent;
    }

    private final void indent(PrintStream out, int n) {
        for (int i = 0; i < n; i++) {
        out.print("  ");
        }
    }

    /**
     * Dumps a debugging representation of the element hierarchy.
         *
         * @param out the output stream
         * @param indentAmount the indentation level >= 0
     */
    public void dump(PrintStream out, int indentAmount) {
        indent(out, indentAmount);
        if (getName() == null) {
        out.print("<??");
        } else {
        out.print("<" + getName());
        }
        if (getAttributeCount() > 0) {
        out.println("");
        // dump the attributes
        Enumeration names = attributes.getAttributeNames();
        while (names.hasMoreElements()) {
            Object name = names.nextElement();
            indent(out, indentAmount + 1);
            out.println(name + "=" + getAttribute(name));
        }
        indent(out, indentAmount);
        }
        out.println(">");

        if (isLeaf()) {
        indent(out, indentAmount+1);
        out.print("[" + getStartOffset() + "," + getEndOffset() + "]");
        Content c = getContent();
        try {
            String contentStr = c.getString(getStartOffset(),
            getEndOffset() - getStartOffset()).trim();
            if (contentStr.length() > 40) {
            contentStr = contentStr.substring(0, 40) + "...";
            }
            out.println(contentStr);
            } catch (BadLocationException e) {
            ;
        }

        } else {
        int n = getElementCount();
        for (int i = 0; i < n; i++) {
            AbstractElement e = (AbstractElement) getElement(i);
            e.dump(out, indentAmount+1);
        }
        }
    }

    // --- Object methods ---------------------------

        /**
         * Finalizes an AbstractElement.
         */
    protected void finalize() throws Throwable {
        AttributeContext context = getAttributeContext();
        context.reclaim(attributes);
    }

    // --- AttributeSet ----------------------------
    // delegated to the immutable field "attributes"

    /**
         * Gets the number of attributes that are defined.
         *
         * @return the number of attributes >= 0
     * @see AttributeSet#getAttributeCount
     */
        public int getAttributeCount() {
        return attributes.getAttributeCount();
    }

    /**
         * Checks whether a given attribute is defined.
         *
         * @param attrName the non-null attribute name
         * @return true if the attribute is defined
     * @see AttributeSet#isDefined
     */
        public boolean isDefined(Object attrName) {
        return attributes.isDefined(attrName);
    }

    /**
         * Checks whether two attribute sets are equal.
         *
         * @param attr the attribute set to check against
         * @return true if the same
     * @see AttributeSet#isEqual
     */
        public boolean isEqual(AttributeSet attr) {
        return attributes.isEqual(attr);
    }

    /**
         * Copies a set of attributes.
         *
         * @return the copy
     * @see AttributeSet#copyAttributes
     */
        public AttributeSet copyAttributes() {
        return attributes;
    }

    /**
         * Gets the value of an attribute.
         *
         * @param attrName the non-null attribute name
         * @return the attribute value
     * @see AttributeSet#getAttribute
     */
        public Object getAttribute(Object attrName) {
        Object value = attributes.getAttribute(attrName);
        if (value == null) {
        // The delegate nor it's resolvers had a match,
        // so we'll try to resolve through the parent
        // element.
        AttributeSet a = (parent != null) ? parent.getAttributes() : null;
        if (a != null) {
            value = a.getAttribute(attrName);
        }
        }
        return value;
    }

    /**
         * Gets the names of all attributes.
         *
         * @return the attribute names as an enumeration
     * @see AttributeSet#getAttributeNames
     */
        public Enumeration getAttributeNames() {
        return attributes.getAttributeNames();
    }

    /**
         * Checks whether a given attribute name/value is defined.
         *
         * @param name the non-null attribute name
         * @param value the attribute value
         * @return true if the name/value is defined
     * @see AttributeSet#containsAttribute
     */
        public boolean containsAttribute(Object name, Object value) {
        return attributes.containsAttribute(name, value);
    }


    /**
         * Checks whether the element contains all the attributes.
         *
         * @param attrs the attributes to check
         * @return true if the element contains all the attributes
     * @see AttributeSet#containsAttributes
     */
        public boolean containsAttributes(AttributeSet attrs) {
        return attributes.containsAttributes(attrs);
    }

    /**
         * Gets the resolving parent.
     * If not overriden, the resolving parent defaults to
     * the parent element.
         *
         * @return the attributes from the parent, null if none
     * @see AttributeSet#getResolveParent
     */
        public AttributeSet getResolveParent() {
        AttributeSet a = attributes.getResolveParent();
        if ((a == null) && (parent != null)) {
        a = parent.getAttributes();
        }
        return a;
    }

    // --- MutableAttributeSet ----------------------------------
    // should fetch a new immutable record for the field
    // "attributes".

    /**
         * Adds an attribute to the element.
         *
         * @param name the non-null attribute name
         * @param value the attribute value
     * @see MutableAttributeSet#addAttribute
     */
        public void addAttribute(Object name, Object value) {
        checkForIllegalCast();
        AttributeContext context = getAttributeContext();
        attributes = context.addAttribute(attributes, name, value);
    }

    /**
         * Adds a set of attributes to the element.
         *
         * @param attr the attributes to add
     * @see MutableAttributeSet#addAttribute
     */
        public void addAttributes(AttributeSet attr) {
        checkForIllegalCast();
        AttributeContext context = getAttributeContext();
        attributes = context.addAttributes(attributes, attr);
    }

    /**
         * Removes an attribute from the set.
         *
         * @param name the non-null attribute name
     * @see MutableAttributeSet#removeAttribute
     */
        public void removeAttribute(Object name) {
        checkForIllegalCast();
        AttributeContext context = getAttributeContext();
        attributes = context.removeAttribute(attributes, name);
    }

    /**
         * Removes a set of attributes for the element.
         *
         * @param names the attribute names
     * @see MutableAttributeSet#removeAttributes
     */
        public void removeAttributes(Enumeration names) {
        checkForIllegalCast();
        AttributeContext context = getAttributeContext();
        attributes = context.removeAttributes(attributes, names);
    }

    /**
         * Removes a set of attributes for the element.
         *
         * @param attrs the attributes
     * @see MutableAttributeSet#removeAttributes
     */
        public void removeAttributes(AttributeSet attrs) {
        checkForIllegalCast();
        AttributeContext context = getAttributeContext();
        if (attrs == this) {
        attributes = context.getEmptySet();
        } else {
        attributes = context.removeAttributes(attributes, attrs);
        }
    }

    /**
         * Sets the resolving parent.
         *
         * @param parent the parent, null if none
     * @see MutableAttributeSet#setResolveParent
     */
        public void setResolveParent(AttributeSet parent) {
        checkForIllegalCast();
        AttributeContext context = getAttributeContext();
        if (parent != null) {
        attributes =
            context.addAttribute(attributes, StyleConstants.ResolveAttribute,
                     parent);
        } else {
        attributes =
            context.removeAttribute(attributes, StyleConstants.ResolveAttribute);
        }
    }

    private final void checkForIllegalCast() {
        Thread t = getCurrentWriter();
        if ((t == null) || (t != Thread.currentThread())) {
        throw new StateInvariantError("Illegal cast to MutableAttributeSet");
        }
    }

        // --- Element methods -------------------------------------

        /**
         * Retrieves the underlying model.
         *
         * @return the model
         */
    public Document getDocument() {
        return AbstractDocument.this;
    }

        /**
         * Gets the parent of the element.
         *
         * @return the parent
         */
    public Element getParentElement() {
        return parent;
    }

        /**
         * Gets the attributes for the element.
         *
         * @return the attribute set
         */
    public AttributeSet getAttributes() {
        return this;
    }

        /**
         * Gets the name of the element.
         *
         * @return the name, null if none
         */
        public String getName() {
        if (attributes.isDefined(ElementNameAttribute)) {
        return (String) attributes.getAttribute(ElementNameAttribute);
        }
        return null;
    }

        /**
         * Gets the starting offset in the model for the element.
         *
         * @return the offset >= 0
         */
    public abstract int getStartOffset();

        /**
         * Gets the ending offset in the model for the element.
         *
         * @return the offset >= 0
         */
    public abstract int getEndOffset();

        /**
         * Gets a child element.
         *
         * @param index the child index, >= 0 && < getElementCount()
         * @return the child element
         */
    public abstract Element getElement(int index);

        /**
         * Gets the number of children for the element.
         *
         * @return the number of children >= 0
         */
    public abstract int getElementCount();

        /**
         * Gets the child element index closest to the given model offset.
         *
         * @param offset the offset >= 0
         * @return the element index >= 0
         */
    public abstract int getElementIndex(int offset);

        /**
         * Checks whether the element is a leaf.
         *
         * @return true if a leaf
         */
    public abstract boolean isLeaf();

    // --- serialization ---------------------------------------------

        private void writeObject(ObjectOutputStream s) throws IOException {
        s.defaultWriteObject();
        StyleContext.writeAttributeSet(s, attributes);
    }

        private void readObject(ObjectInputStream s)
            throws ClassNotFoundException, IOException
        {
        s.defaultReadObject();
        MutableAttributeSet attr = new SimpleAttributeSet();
        StyleContext.readAttributeSet(s, attr);
        AttributeContext context = getAttributeContext();
        attributes = context.addAttributes(SimpleAttributeSet.EMPTY, attr);
    }

    // ---- variables -----------------------------------------------------

    private Element parent;
    private transient AttributeSet attributes;

    }

    /**
     * Implements a composite element that contains other elements.
     * <p>
     * Warning: serialized objects of this class will not be compatible with
     * future swing releases.  The current serialization support is appropriate
     * for short term storage or RMI between Swing1.0 applications.  It will
     * not be possible to load serialized Swing1.0 objects with future releases
     * of Swing.  The JDK1.2 release of Swing will be the compatibility
     * baseline for the serialized form of Swing objects.
     */
    public class BranchElement extends AbstractElement {

    /**
     * Constructs a composite element that initially contains
     * no children.
     *
     * @param parent  The parent element
         * @param a the attributes for the element
     */
    public BranchElement(Element parent, AttributeSet a) {
        super(parent, a);
        children = new AbstractElement[1];
        nchildren = 0;
        lastIndex = -1;
    }

    /**
     * Gets the child element that contains
     * the given model position.
         *
         * @param pos the position >= 0
         * @return the element, null if none
     */
    public Element positionToElement(int pos) {
        int index = getElementIndex(pos);
        Element child = children[index];
        int p0 = child.getStartOffset();
        int p1 = child.getEndOffset();
        if ((pos >= p0) && (pos < p1)) {
        return child;
        }
        return null;
    }

        /**
         * Replaces content with a new set of elements.
         *
         * @param offset the starting offset >= 0
         * @param length the length to replace >= 0
         * @param elems the new elements
         */
        public void replace(int offset, int length, Element[] elems) {
        int delta = elems.length - length;
        int src = offset + length;
        int nmove = nchildren - src;
        int dest = src + delta;
        if ((nchildren + delta) >= children.length) {
        // need to grow the array
        int newLength = Math.max(2*children.length, nchildren + delta);
        AbstractElement[] newChildren = new AbstractElement[newLength];
        System.arraycopy(children, 0, newChildren, 0, offset);
        System.arraycopy(elems, 0, newChildren, offset, elems.length);
        System.arraycopy(children, src, newChildren, dest, nmove);
        children = newChildren;
        } else {
        // patch the existing array
        System.arraycopy(children, src, children, dest, nmove);
        System.arraycopy(elems, 0, children, offset, elems.length);
        }
        nchildren = nchildren + delta;
    }

        /**
         * Converts the element to a string.
         *
         * @return the string
         */
    public String toString() {
        return "BranchElement(" + getName() + ") " + getStartOffset() + "," +
        getEndOffset() + "\n";
    }

    // --- Element methods -----------------------------------

        /**
         * Gets the element name.
         *
         * @return the element name
         */
    public String getName() {
        String nm = super.getName();
        if (nm == null) {
        nm = ParagraphElementName;
        }
        return nm;
    }

        /**
         * Gets the starting offset in the model for the element.
         *
         * @return the offset >= 0
         */
        public int getStartOffset() {
        return children[0].getStartOffset();
    }

        /**
         * Gets the ending offset in the model for the element.
         *
         * @return the offset >= 0
         */
        public int getEndOffset() {
        Element child = children[nchildren - 1];
        return child.getEndOffset();
    }

        /**
         * Gets a child element.
         *
         * @param index the child index, >= 0 && < getElementCount()
         * @return the child element, null if none
         */
    public Element getElement(int index) {
        if (index < nchildren) {
        return children[index];
        }
        return null;
    }

        /**
         * Gets the number of children for the element.
         *
         * @return the number of children >= 0
         */
    public int getElementCount()  {
        return nchildren;
    }

        /**
         * Gets the child element index closest to the given model offset.
         *
         * @param offset the offset >= 0
         * @return the element index >= 0
         */
    public int getElementIndex(int offset) {
        int index;
        int lower = 0;
        int upper = nchildren - 1;
        int mid = 0;
        int p0 = getStartOffset();
        int p1;

        if (nchildren == 0) {
        return 0;
        }
        if (offset >= getEndOffset()) {
        return nchildren - 1;
        }

        // see if the last index can be used.
        if ((lastIndex >= lower) && (lastIndex <= upper)) {
        Element lastHit = children[lastIndex];
        p0 = lastHit.getStartOffset();
        p1 = lastHit.getEndOffset();
        if ((offset >= p0) && (offset < p1)) {
            return lastIndex;
        }

        // last index wasn't a hit, but it does give useful info about
        // where a hit (if any) would be.
        if (offset < p0) {
            upper = lastIndex;
        } else  {
            lower = lastIndex;
        }
        }

        while (lower <= upper) {
        mid = lower + ((upper - lower) / 2);
        Element elem = children[mid];
        p0 = elem.getStartOffset();
        p1 = elem.getEndOffset();
        if ((offset >= p0) && (offset < p1)) {
            // found the location
            index = mid;
            lastIndex = index;
            return index;
        } else if (offset < p0) {
            upper = mid - 1;
        } else {
            lower = mid + 1;
        }
        }

        // didn't find it, but we indicate the index of where it would belong
        if (offset < p0) {
        index = mid;
        } else {
        index = mid + 1;
        }
        lastIndex = index;
        return index;
    }

        /**
         * Checks whether the element is a leaf.
         *
         * @return true if a leaf
         */
    public boolean isLeaf() {
        return false;
    }

    // ------ members ----------------------------------------------

    private AbstractElement[] children;
    private int nchildren;
    private int lastIndex;
    }

    /**
     * Implements an element that directly represents content of
     * some kind.
     * <p>
     * Warning: serialized objects of this class will not be compatible with
     * future swing releases.  The current serialization support is appropriate
     * for short term storage or RMI between Swing1.0 applications.  It will
     * not be possible to load serialized Swing1.0 objects with future releases
     * of Swing.  The JDK1.2 release of Swing will be the compatibility
     * baseline for the serialized form of Swing objects.
     *
     * @see     Element
     */
    public class LeafElement extends AbstractElement {

    /**
     * Constructs an element that represents content within the
     * document (has no children).
     *
     * @param parent  The parent element
     * @param a       The element attributes
     * @param offs0   The start offset >= 0
     * @param offs1   The end offset >= offs0
     */
    public LeafElement(Element parent, AttributeSet a, int offs0, int offs1) {
        super(parent, a);
        try {
        p0 = createPosition(offs0);
        p1 = createPosition(offs1);
        } catch (BadLocationException e) {
        p0 = null;
        p1 = null;
        throw new StateInvariantError("Can't create Position references");
        }
    }

        /**
         * Converts the element to a string.
         *
         * @return the string
         */
    public String toString() {
        return "LeafElement(" + getName() + ") " + p0 + "," + p1 + "\n";
    }

    // --- Element methods ---------------------------------------------

        /**
         * Gets the starting offset in the model for the element.
         *
         * @return the offset >= 0
         */
    public int getStartOffset() {
        return p0.getOffset();
    }

        /**
         * Gets the ending offset in the model for the element.
         *
         * @return the offset >= 0
         */
    public int getEndOffset() {
        return p1.getOffset();
    }

        /**
         * Gets the element name.
         *
         * @return the name
         */
    public String getName() {
        String nm = super.getName();
        if (nm == null) {
        nm = ContentElementName;
        }
        return nm;
    }

        /**
         * Gets the child element index closest to the given model offset.
         *
         * @param pos the offset >= 0
         * @return the element index >= 0
         */
    public int getElementIndex(int pos) {
        return -1;
    }

        /**
         * Gets a child element.
         *
         * @param index the child index, >= 0 && < getElementCount()
         * @return the child element
         */
    public Element getElement(int index) {
        return null;
    }

        /**
         * Returns the number of child elements.
         *
         * @return the number of children >= 0
         */
    public int getElementCount()  {
        return 0;
    }

        /**
         * Checks whether the element is a leaf.
         *
         * @return true if a leaf
         */
    public boolean isLeaf() {
        return true;
    }

    // --- serialization ---------------------------------------------

        private void writeObject(ObjectOutputStream s) throws IOException {
        s.defaultWriteObject();
        s.writeInt(p0.getOffset());
        s.writeInt(p1.getOffset());
    }

        private void readObject(ObjectInputStream s)
            throws ClassNotFoundException, IOException
        {
        s.defaultReadObject();

        // set the range with positions that track change
        int off0 = s.readInt();
        int off1 = s.readInt();
        try {
        p0 = createPosition(off0);
        p1 = createPosition(off1);
        } catch (BadLocationException e) {
        p0 = null;
        p1 = null;
        throw new IOException("Can't restore Position references");
        }
    }

    // ---- members -----------------------------------------------------

    private transient Position p0;
    private transient Position p1;
    }

    /**
     * Stores document changes as the document is being
     * modified.  Can subsequently be used for change notification
     * when done with the document modification transaction.
     * This is used by the AbstractDocument class and its extensions
     * for broadcasting change information to the document listeners.
     */
    public class DefaultDocumentEvent extends CompoundEdit implements DocumentEvent {

    /**
     * Constructs a change record.
     *
     * @param offs the offset into the document of the change >= 0
     * @param len  the length of the change >= 0
     * @param type the type of event (DocumentEvent.EventType)
     */
        public DefaultDocumentEvent(int offs, int len, DocumentEvent.EventType type) {
        super();
        offset = offs;
        length = len;
        this.type = type;
    }

    /**
     * Returns a string description of the change event.
     *
     * @return a string
     */
        public String toString() {
        return edits.toString();
    }

    // --- CompoundEdit methods --------------------------

    /**
     * Adds a document edit.  If the number of edits crosses
     * a threshold, this switches on a hashtable lookup for
     * ElementChange implementations since access of these
     * needs to be relatively quick.
     *
     * @param anEdit a document edit record
     * @return true if the edit was added
     */
        public boolean addEdit(UndoableEdit anEdit) {
        // if the number of changes gets too great, start using
        // a hashtable for to locate the change for a given element.
        if ((changeLookup == null) && (edits.size() > 10)) {
        changeLookup = new Hashtable();
        int n = edits.size();
        for (int i = 0; i < n; i++) {
            Object o = edits.elementAt(i);
            if (o instanceof DocumentEvent.ElementChange) {
            DocumentEvent.ElementChange ec = (DocumentEvent.ElementChange) o;
            changeLookup.put(ec.getElement(), ec);
            }
        }
        }

        // if we have a hashtable... add the entry if it's
        // an ElementChange.
        if ((changeLookup != null) && (anEdit instanceof DocumentEvent.ElementChange)) {
        DocumentEvent.ElementChange ec = (DocumentEvent.ElementChange) anEdit;
        changeLookup.put(ec.getElement(), ec);
        }
        return super.addEdit(anEdit);
    }

    /**
     * Redoes a change.
     *
     * @exception CannotRedoException if the change cannot be redone
     */
        public void redo() throws CannotRedoException {
        writeLock();
        try {
        // change the state
        super.redo();
        // fire a DocumentEvent to notify the view(s)
        if (type == DocumentEvent.EventType.INSERT) {
            fireInsertUpdate(this);
        } else if (type == DocumentEvent.EventType.REMOVE) {
            fireRemoveUpdate(this);
        } else {
            fireChangedUpdate(this);
        }
        } finally {
        writeUnlock();
        }
    }

    /**
     * Undoes a change.
     *
     * @exception CannotUndoException if the change cannot be undone
     */
        public void undo() throws CannotUndoException {
        writeLock();
        try {
        // change the state
        super.undo();
        // fire a DocumentEvent to notify the view(s)
        if (type == DocumentEvent.EventType.REMOVE) {
            fireInsertUpdate(this);
        } else if (type == DocumentEvent.EventType.INSERT) {
            fireRemoveUpdate(this);
        } else {
            fireChangedUpdate(this);
        }
        } finally {
        writeUnlock();
        }
    }

    /**
     * DefaultDocument events are significant.  If you wish to aggregate
     * DefaultDocumentEvents to present them as a single edit to the user
     * place them into a CompoundEdit.
         *
         * @return whether the event is significant for edit undo purposes
     */
    public boolean isSignificant() {
        return true;
    }


    /**
     * Provides a localized, human readable description of this edit
     * suitable for use in, say, a change log.
         *
         * @return the description
     */
    public String getPresentationName() {
        DocumentEvent.EventType type = getType();
        if(type == DocumentEvent.EventType.INSERT)
        return "addition";
        if(type == DocumentEvent.EventType.REMOVE)
        return "deletion";
        return "style change";
    }

    /**
     * Provides a localized, human readable description of the undoable
     * form of this edit, e.g. for use as an Undo menu item. Typically
     * derived from getDescription();
         *
         * @return the description
     */
    public String getUndoPresentationName() {
        return "Undo " + getPresentationName();
    }

    /**
     * Provides a localized, human readable description of the redoable
     * form of this edit, e.g. for use as a Redo menu item. Typically
     * derived from getPresentationName();
         *
         * @return the description
     */
    public String getRedoPresentationName() {
        return "Redo " + getPresentationName();
    }

    // --- DocumentEvent methods --------------------------

    /**
     * Returns the type of event.
         *
         * @return the event type as a DocumentEvent.EventType
     * @see DocumentEvent#getType
     */
    public DocumentEvent.EventType getType() {
        return type;
    }

    /**
     * Returns the offset within the document of the start of the change.
     *
     * @return the offset >= 0
     * @see DocumentEvent#getOffset
     */
        public int getOffset() {
        return offset;
    }

    /**
     * Returns the length of the change.
     *
     * @return the length >= 0
     * @see DocumentEvent#getLength
     */
        public int getLength() {
        return length;
    }

    /**
     * Gets the document that sourced the change event.
     *
     * @return the document
     * @see DocumentEvent#getDocument
     */
        public Document getDocument() {
        return AbstractDocument.this;
    }

    /**
     * Gets the changes for an element.
     *
     * @param elem the element
     * @return the changes
     */
        public DocumentEvent.ElementChange getChange(Element elem) {
        if (changeLookup != null) {
        return (DocumentEvent.ElementChange) changeLookup.get(elem);
        }
        int n = edits.size();
        for (int i = 0; i < n; i++) {
        Object o = edits.elementAt(i);
        if (o instanceof DocumentEvent.ElementChange) {
            DocumentEvent.ElementChange c = (DocumentEvent.ElementChange) o;
            if (c.getElement() == elem) {
            return c;
            }
        }
        }
        return null;
    }

    // --- member variables ------------------------------------

        private int offset;
        private int length;
        private Hashtable changeLookup;
    private DocumentEvent.EventType type;

    }

    /**
     * An implementation of ElementChange that can be added to the document
     * event.
     */
    public static class ElementEdit extends AbstractUndoableEdit implements DocumentEvent.ElementChange {

    /**
     * Constructs an edit record.  This does not modify the element
     * so it can safely be used to <em>catch up</em> a view to the
     * current model state for views that just attached to a model.
     *
     * @param e the element
     * @param index the index into the model >= 0
     * @param removed a set of elements that were removed
     * @param added a set of elements that were added
     */
        public ElementEdit(Element e, int index, Element[] removed, Element[] added) {
        super();
        this.e = e;
        this.index = index;
        this.removed = removed;
        this.added = added;
    }

    /**
     * Returns the underlying element.
     *
     * @return the element
     */
        public Element getElement() {
        return e;
    }

    /**
     * Returns the index into the list of elements.
     *
     * @return the index >= 0
     */
        public int getIndex() {
        return index;
    }

    /**
     * Gets a list of children that were removed.
     *
     * @return the list
     */
        public Element[] getChildrenRemoved() {
        return removed;
    }

    /**
     * Gets a list of children that were added.
     *
     * @return the list
     */
        public Element[] getChildrenAdded() {
        return added;
    }

    /**
     * Redoes a change.
     *
     * @exception CannotRedoException if the change cannot be redone
     */
        public void redo() throws CannotRedoException {
        super.redo();

        // Since this event will be reused, switch around added/removed.
        Element[] tmp = removed;
        removed = added;
        added = tmp;

        // PENDING(prinz) need MutableElement interface, canRedo() should check
        ((AbstractDocument.BranchElement)e).replace(index, removed.length, added);
    }

    /**
     * Undoes a change.
     *
     * @exception CannotUndoException if the change cannot be undone
     */
        public void undo() throws CannotUndoException {
        super.undo();
        // PENDING(prinz) need MutableElement interface, canUndo() should check
        ((AbstractDocument.BranchElement)e).replace(index, added.length, removed);

        // Since this event will be reused, switch around added/removed.
        Element[] tmp = removed;
        removed = added;
        added = tmp;
    }

        private Element e;
    private int index;
    private Element[] removed;
    private Element[] added;
    }

}