Module java.desktop

Package javax.swing.undo

Interface UndoableEdit

All Known Implementing Classes:

AbstractDocument.DefaultDocumentEvent, AbstractDocument.ElementEdit, AbstractUndoableEdit, CompoundEdit, DefaultStyledDocument.AttributeUndoableEdit, StateEdit, UndoManager

public interface UndoableEdit

An UndoableEdit represents an edit. The edit may be undone, or if already undone the edit may be redone.

UndoableEdit is designed to be used with the UndoManager. As UndoableEdits are generated by an UndoableEditListener they are typically added to the UndoManager. When an UndoableEdit is added to an UndoManager the following occurs (assuming end has not been called on the UndoManager):

1. If the UndoManager contains edits it will call addEdit on the current edit passing in the new edit as the argument. If addEdit 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 addEdit as a way for smaller edits to be incorporated into a larger edit and treated as a single edit.
2. If addEdit returns false replaceEdit is called on the new edit with the current edit passed in as the argument. This is the inverse of addEdit — if the new edit returns true from replaceEdit, the new edit replaces the current edit.

The UndoManager makes use of isSignificant to determine how many edits should be undone or redone. The UndoManager will undo or redo all insignificant edits (isSignificant returns false) between the current edit and the last or next significant edit. addEdit and replaceEdit can be used to treat multiple edits as a single edit, returning false from isSignificant allows for treating can be used to have many smaller edits undone or redone at once. Similar functionality can also be done using the addEdit method.

Method Summary

Modifier and Type	Method	Description
boolean	addEdit(UndoableEdit anEdit)	Adds an UndoableEdit to this UndoableEdit.
boolean	canRedo()	Returns true if this edit may be redone.
boolean	canUndo()	Returns true if this edit may be undone.
void	die()	Informs the edit that it should no longer be used.
String	getPresentationName()	Returns a localized, human-readable description of this edit, suitable for use in a change log, for example.
String	getRedoPresentationName()	Returns a localized, human-readable description of the redoable form of this edit, suitable for use as a Redo menu item, for example.
String	getUndoPresentationName()	Returns a localized, human-readable description of the undoable form of this edit, suitable for use as an Undo menu item, for example.
boolean	isSignificant()	Returns true if this edit is considered significant.
void	redo()	Re-applies the edit.
boolean	replaceEdit(UndoableEdit anEdit)	Returns true if this UndoableEdit should replace anEdit.
void	undo()	Undo the edit.

Method Details

undo

void undo()
   throws CannotUndoException

Undo the edit.

Throws:

CannotUndoException - if this edit can not be undone

canUndo

boolean canUndo()

Returns true if this edit may be undone.

Returns:

true if this edit may be undone

redo

void redo()
   throws CannotRedoException

Re-applies the edit.

Throws:

CannotRedoException - if this edit can not be redone

canRedo

boolean canRedo()

Returns true if this edit may be redone.

Returns:

true if this edit may be redone

die

void die()

Informs the edit that it should no longer be used. Once an UndoableEdit has been marked as dead it can no longer be undone or redone.

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. UndoManager calls this before it dequeues edits.

Note that this is a one-way operation. There is no "un-die" method.

See Also:

• CompoundEdit.die()

addEdit

boolean addEdit(UndoableEdit anEdit)

Adds an UndoableEdit to this UndoableEdit. 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 UndoableEdit would override addEdit to return true when the edits may be coalesced.

A return value of true indicates anEdit was incorporated into this edit. A return value of false indicates anEdit may not be incorporated into this edit.

Typically the receiver is already in the queue of a UndoManager (or other UndoableEditListener), and is being given a chance to incorporate anEdit rather than letting it be added to the queue in turn.

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.

Parameters:

anEdit - the edit to be added

Returns:

true if anEdit may be incorporated into this edit

replaceEdit

boolean replaceEdit(UndoableEdit anEdit)

Returns true if this UndoableEdit should replace anEdit. This method is used by CompoundEdit and the UndoManager; it is called if anEdit could not be added to the current edit (addEdit returns false).

This method provides a way for an edit to replace an existing edit.

This message is the opposite of addEdit--anEdit has typically already been queued in an UndoManager (or other UndoableEditListener), and the receiver is being given a chance to take its place.

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().

Parameters:

anEdit - the edit that replaces the current edit

Returns:

true if this edit should replace anEdit

isSignificant

boolean isSignificant()

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 UndoManager will undo, or redo, all insignificant edits to the next significant edit.

Returns:

true if this edit is significant

getPresentationName

String getPresentationName()

Returns a localized, human-readable description of this edit, suitable for use in a change log, for example.

Returns:

description of this edit

getUndoPresentationName

String getUndoPresentationName()

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 getPresentationName.

Returns:

a description of the undoable form of this edit

getRedoPresentationName

String getRedoPresentationName()

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 getPresentationName.

Returns:

a description of the redoable form of this edit