# 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 `UndoableEdit`s 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