gcc/libjava/classpath/javax/swing/undo/UndoableEditSupport.java

/* UndoableEditSupport.java --
   Copyright (C) 2002, 2003, 2004, 2005, 2006,  Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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permission to link this library with independent modules to produce an
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package javax.swing.undo;

import java.util.Iterator;
import java.util.Vector;

import javax.swing.event.UndoableEditEvent;
import javax.swing.event.UndoableEditListener;

/**
 * A helper class for supporting {@link
 * javax.swing.event.UndoableEditListener}.
 *
 * @author Andrew Selkirk (aselkirk@sympatico.ca)
 * @author Sascha Brawer (brawer@dandelis.ch)
 */
public class UndoableEditSupport
{
  /**
   * The number of times that {@link #beginUpdate()} has been called
   * without a matching call to {@link #endUpdate()}.
   */
  protected int updateLevel;


  /**
   * compoundEdit
   */
  protected CompoundEdit compoundEdit;


  /**
   * The currently registered listeners.
   */
  protected Vector<UndoableEditListener> listeners =
    new Vector<UndoableEditListener>();


  /**
   * The source of the broadcast UndoableEditEvents.
   */
  protected Object realSource;


  /**
   * Constructs a new helper for broadcasting UndoableEditEvents.  The
   * events will indicate the newly constructed
   * <code>UndoableEditSupport</code> instance as their source.
   *
   * @see #UndoableEditSupport(java.lang.Object)
   */
  public UndoableEditSupport()
  {
    realSource = this;
  }


  /**
   * Constructs a new helper for broadcasting UndoableEditEvents.
   *
   * @param realSource the source of the UndoableEditEvents that will
   * be broadcast by this helper. If <code>realSource</code> is
   * <code>null</code>, the events will indicate the newly constructed
   * <code>UndoableEditSupport</code> instance as their source.
   */
  public UndoableEditSupport(Object realSource)
  {
    if (realSource == null)
      realSource = this;
    this.realSource = realSource;
  }


  /**
   * Returns a string representation of this object that may be useful
   * for debugging.
   */
  public String toString()
  {
    // Note that often, this.realSource == this. Therefore, dumping
    // realSource without additional checks may lead to infinite
    // recursion. See Classpath bug #7119.
    return super.toString() + " updateLevel: " + updateLevel
      + " listeners: " + listeners + " compoundEdit: " + compoundEdit;
  }


  /**
   * Registers a listener.
   *
   * @param val the listener to be added.
   */
  public synchronized void addUndoableEditListener(UndoableEditListener val)
  {
    listeners.add(val);
  }


  /**
   * Unregisters a listener.
   * @param val the listener to be removed.
   */
  public synchronized void removeUndoableEditListener(UndoableEditListener val)
  {
    listeners.removeElement(val);
  }


  /**
   * Returns an array containing the currently registered listeners.
   */
  public synchronized UndoableEditListener[] getUndoableEditListeners()
  {
    UndoableEditListener[] result = new UndoableEditListener[listeners.size()];
    return listeners.toArray(result);
  }


  /**
   * Notifies all registered listeners that an {@link
   * UndoableEditEvent} has occured.
   *
   * <p><b>Lack of Thread Safety:</b> It is <em>not</em> safe to call
   * this method from concurrent threads, unless the call is protected
   * by a synchronization on this <code>UndoableEditSupport</code>
   * instance.
   *
   * @param edit the edit action to be posted.
   */
  protected void _postEdit(UndoableEdit edit)
  {
    UndoableEditEvent event;
    Iterator<UndoableEditListener> iter;

    // Do nothing if we have no listeners.
    if (listeners.isEmpty())
      return;

    event = new UndoableEditEvent(realSource, edit);

    // We clone the vector because this allows listeners to register
    // or unregister listeners in their undoableEditHappened method.
    // Otherwise, this would throw exceptions (in the case of
    // Iterator, a java.util.ConcurrentModificationException; in the
    // case of a direct loop over the Vector elements, some
    // index-out-of-bounds exception).
    iter = new Vector<UndoableEditListener>(listeners).iterator();
    while (iter.hasNext())
      iter.next().undoableEditHappened(event);
  }


  /**
   * If {@link #beginUpdate} has been called (so that the current
   * update level is greater than zero), adds the specified edit
   * to {@link #compoundEdit}. Otherwise, notify listeners of the
   * edit by calling {@link #_postEdit(UndoableEdit)}.
   *
   * <p><b>Thread Safety:</b> It is safe to call this method from any
   * thread without external synchronization.
   *
   * @param edit the edit action to be posted.
   */
  public synchronized void postEdit(UndoableEdit edit)
  {
    if (compoundEdit != null)
      compoundEdit.addEdit(edit);
    else
      _postEdit(edit);
  }


  /**
   * Returns the current update level.
   */
  public int getUpdateLevel()
  {
    return updateLevel;
  }


  /**
   * Starts a (possibly nested) update session. If the current update
   * level is zero, {@link #compoundEdit} is set to the result of the
   * {@link #createCompoundEdit} method. In any case, the update level
   * is increased by one.
   *
   * <p><b>Thread Safety:</b> It is safe to call this method from any
   * thread without external synchronization.
   */
  public synchronized void beginUpdate()
  {
    if (compoundEdit == null)
      compoundEdit = createCompoundEdit();
    ++updateLevel;
  }


  /**
   * Creates a new instance of {@link CompoundEdit}. Called by {@link
   * #beginUpdate}. If a subclass wants {@link #beginUpdate} to work
   * on a specific {@link #compoundEdit}, it should override this
   * method.
   *
   * @return a newly created instance of {@link CompoundEdit}.
   */
  protected CompoundEdit createCompoundEdit()
  {
    return new CompoundEdit();
  }


  /**
   * Ends an update session. If the terminated session was the
   * outermost session, {@link #compoundEdit} will receive an
   * <code>end</code> message, and {@link #_postEdit} gets called in
   * order to notify any listeners. Finally, the
   * <code>compoundEdit</code> is discarded.
   *
   * <p><b>Thread Safety:</b> It is safe to call this method from any
   * thread without external synchronization.
   */
  public synchronized void endUpdate()
  {
    if (updateLevel == 0)
      throw new IllegalStateException();

    if (--updateLevel > 0)
      return;

    compoundEdit.end();
    _postEdit(compoundEdit);
    compoundEdit = null;
  }
}