src/share/classes/javax/swing/undo/UndoableEdit.java

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package javax.swing.undo;

import javax.swing.event.*;

/**
 * An <code>UndoableEdit</code> represents an edit.  The edit may
 * be undone, or if already undone the edit may be redone.
 * <p>
 * <code>UndoableEdit</code> is designed to be used with the
 * <code>UndoManager</code>.  As <code>UndoableEdit</code>s are generated
 * by an <code>UndoableEditListener</code> they are typically added to
 * the <code>UndoManager</code>.  When an <code>UndoableEdit</code>
 * is added to an <code>UndoManager</code> the following occurs (assuming
 * <code>end</code> has not been called on the <code>UndoManager</code>):
 * <ol>
 * <li>If the <code>UndoManager</code> contains edits it will call
 *     <code>addEdit</code> on the current edit passing in the new edit
 *     as the argument.  If <code>addEdit</code> returns true the
 *     new edit is assumed to have been incorporated into the current edit and
 *     the new edit will not be added to the list of current edits.
 *     Edits can use <code>addEdit</code> as a way for smaller edits to
 *     be incorporated into a larger edit and treated as a single edit.
 * <li>If <code>addEdit</code> returns false <code>replaceEdit</code>
 *     is called on the new edit with the current edit passed in as the
 *     argument. This is the inverse of <code>addEdit</code> &#151;
 *     if the new edit returns true from <code>replaceEdit</code>, the new
 *     edit replaces the current edit.
 * </ol>
 * The <code>UndoManager</code> makes use of
 * <code>isSignificant</code> to determine how many edits should be
 * undone or redone.  The <code>UndoManager</code> will undo or redo
 * all insignificant edits (<code>isSignificant</code> returns false)
 * between the current edit and the last or
 * next significant edit.   <code>addEdit</code> and
 * <code>replaceEdit</code> can be used to treat multiple edits as
 * a single edit, returning false from <code>isSignificant</code>
 * allows for treating can be used to
 * have many smaller edits undone or redone at once.  Similar functionality
 * can also be done using the <code>addEdit</code> method.
 *
 * @author Ray Ryan
 */
public interface UndoableEdit {
    /**
     * Undo the edit.
     *
     * @throws CannotUndoException if this edit can not be undone
     */
    public void undo() throws CannotUndoException;

    /**
     * Returns true if this edit may be undone.
     *
     * @return true if this edit may be undone
     */
    public boolean canUndo();

    /**
     * Re-applies the edit.
     *
     * @throws CannotRedoException if this edit can not be redone
     */
    public void redo() throws CannotRedoException;

    /**
     * Returns true if this edit may be redone.
     *
     * @return true if this edit may be redone
     */
    public boolean canRedo();

    /**
     * Informs the edit that it should no longer be used. Once an
     * <code>UndoableEdit</code> has been marked as dead it can no longer
     * be undone or redone.
     * <p>
     * This is a useful hook for cleaning up state no longer
     * needed once undoing or redoing is impossible--for example,
     * deleting file resources used by objects that can no longer be
     * undeleted. <code>UndoManager</code> calls this before it dequeues edits.
     * <p>
     * Note that this is a one-way operation. There is no "un-die"
     * method.
     *
     * @see CompoundEdit#die
     */
    public void die();

    /**
     * Adds an <code>UndoableEdit</code> to this <code>UndoableEdit</code>.
     * This method can be used to coalesce smaller edits into a larger
     * compound edit.  For example, text editors typically allow
     * undo operations to apply to words or sentences.  The text
     * editor may choose to generate edits on each key event, but allow
     * those edits to be coalesced into a more user-friendly unit, such as
     * a word. In this case, the <code>UndoableEdit</code> would
     * override <code>addEdit</code> to return true when the edits may
     * be coalesced.
     * <p>
     * A return value of true indicates <code>anEdit</code> was incorporated
     * into this edit.  A return value of false indicates <code>anEdit</code>
     * may not be incorporated into this edit.
     * <p>Typically the receiver is already in the queue of a
     * <code>UndoManager</code> (or other <code>UndoableEditListener</code>),
     * and is being given a chance to incorporate <code>anEdit</code>
     * rather than letting it be added to the queue in turn.</p>
     *
     * <p>If true is returned, from now on <code>anEdit</code> must return
     * false from <code>canUndo</code> and <code>canRedo</code>,
     * and must throw the appropriate exception on <code>undo</code> or
     * <code>redo</code>.</p>
     *
     * @param anEdit the edit to be added
     * @return true if <code>anEdit</code> may be incorporated into this
     *              edit
     */
    public boolean addEdit(UndoableEdit anEdit);

    /**
     * Returns true if this <code>UndoableEdit</code> should replace
     * <code>anEdit</code>. This method is used by <code>CompoundEdit</code>
     * and the <code>UndoManager</code>; it is called if
     * <code>anEdit</code> could not be added to the current edit
     * (<code>addEdit</code> returns false).
     * <p>
     * This method provides a way for an edit to replace an existing edit.
     * <p>This message is the opposite of addEdit--anEdit has typically
     * already been queued in an <code>UndoManager</code> (or other
     * UndoableEditListener), and the receiver is being given a chance
     * to take its place.</p>
     *
     * <p>If true is returned, from now on anEdit must return false from
     * canUndo() and canRedo(), and must throw the appropriate
     * exception on undo() or redo().</p>
     *
     * @param anEdit the edit that replaces the current edit
     * @return true if this edit should replace <code>anEdit</code>
     */
    public boolean replaceEdit(UndoableEdit anEdit);

    /**
     * Returns true if this edit is considered significant.  A significant
     * edit is typically an edit that should be presented to the user, perhaps
     * on a menu item or tooltip.  The <code>UndoManager</code> will undo,
     * or redo, all insignificant edits to the next significant edit.
     *
     * @return true if this edit is significant
     */
    public boolean isSignificant();

    /**
     * Returns a localized, human-readable description of this edit, suitable
     * for use in a change log, for example.
     *
     * @return description of this edit
     */
    public String getPresentationName();

    /**
     * Returns a localized, human-readable description of the undoable form of
     * this edit, suitable for use as an Undo menu item, for example.
     * This is typically derived from <code>getPresentationName</code>.
     *
     * @return a description of the undoable form of this edit
     */
    public String getUndoPresentationName();

    /**
     * Returns a localized, human-readable description of the redoable form of
     * this edit, suitable for use as a Redo menu item, for example. This is
     * typically derived from <code>getPresentationName</code>.
     *
     * @return a description of the redoable form of this edit
     */
    public String getRedoPresentationName();
}