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/OpenJDK 21

Class UndoManager

java.lang.Object
javax.swing.undo.AbstractUndoableEdit
javax.swing.undo.CompoundEdit
javax.swing.undo.UndoManager
All Implemented Interfaces:
Serializable, EventListener, UndoableEditListener, UndoableEdit 
public class UndoManager extends CompoundEdit implements UndoableEditListener
UndoManager manages a list of UndoableEdits, providing a way to undo or redo the appropriate edits. There are two ways to add edits to an UndoManager. Add the edit directly using the addEdit method, or add the UndoManager to a bean that supports UndoableEditListener. The following examples creates an UndoManager and adds it as an UndoableEditListener to a JTextField: 
   UndoManager undoManager = new UndoManager();
   JTextField tf = ...;
   tf.getDocument().addUndoableEditListener(undoManager);

UndoManager maintains an ordered list of edits and the index of the next edit in that list. The index of the next edit is either the size of the current list of edits, or if undo has been invoked it corresponds to the index of the last significant edit that was undone. When undo is invoked all edits from the index of the next edit to the last significant edit are undone, in reverse order. For example, consider an UndoManager consisting of the following edits: A b c D. Edits with a upper-case letter in bold are significant, those in lower-case and italicized are insignificant.

Figure 1
Figure 1

As shown in figure 1, if D was just added, the index of the next edit will be 4. Invoking undo results in invoking undo on D and setting the index of the next edit to 3 (edit c), as shown in the following figure.

Figure 2
Figure 2

The last significant edit is A, so that invoking undo again invokes undo on c, b, and A, in that order, setting the index of the next edit to 0, as shown in the following figure.

Figure 3
Figure 3

Invoking redo results in invoking redo on all edits between the index of the next edit and the next significant edit (or the end of the list). Continuing with the previous example if redo were invoked, redo would in turn be invoked on A, b and c. In addition the index of the next edit is set to 3 (as shown in figure 2).

Adding an edit to an UndoManager results in removing all edits from the index of the next edit to the end of the list. Continuing with the previous example, if a new edit, e, is added the edit D is removed from the list (after having die invoked on it). If c is not incorporated by the next edit (c.addEdit(e) returns true), or replaced by it (e.replaceEdit(c) returns true), the new edit is added after c, as shown in the following figure.

Figure 4
Figure 4

Once end has been invoked on an UndoManager the superclass behavior is used for all UndoableEdit methods. Refer to CompoundEdit for more details on its behavior.

Unlike the rest of Swing, this class is thread safe.

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 applications running the same version of Swing. As of 1.4, support for long term storage of all JavaBeans has been added to the java.beans package. Please see XMLEncoder.

Field Summary

Fields declared in class javax.swing.undo.CompoundEdit

edits

Fields declared in class javax.swing.undo.AbstractUndoableEdit

RedoName, UndoName

Constructor Summary

Constructor Description
UndoManager()
Creates a new UndoManager.

Method Summary

Modifier and Type Method Description
boolean addEdit(UndoableEdit anEdit)
Adds an UndoableEdit to this UndoManager, if it's possible.
boolean canRedo()
Returns true if edits may be redone.
boolean canUndo()
Returns true if edits may be undone.
boolean canUndoOrRedo()
Returns true if it is possible to invoke undo or redo.
void discardAllEdits()
Empties the undo manager sending each edit a die message in the process.
protected UndoableEdit editToBeRedone()
Returns the next significant edit to be redone if redo is invoked.
protected UndoableEdit editToBeUndone()
Returns the next significant edit to be undone if undo is invoked.
void end()
Turns this UndoManager into a normal CompoundEdit.
int getLimit()
Returns the maximum number of edits this UndoManager holds.
String getRedoPresentationName()
Returns a description of the redoable form of this edit.
String getUndoOrRedoPresentationName()
Convenience method that returns either getUndoPresentationName or getRedoPresentationName.
String getUndoPresentationName()
Returns a description of the undoable form of this edit.
void redo()
Redoes the appropriate edits.
protected void redoTo(UndoableEdit edit)
Redoes all changes from the index of the next edit to edit, updating the index of the next edit appropriately.
void setLimit(int l)
Sets the maximum number of edits this UndoManager holds.
String toString()
Returns a string that displays and identifies this object's properties.
protected void trimEdits(int from, int to)
Removes edits in the specified range.
protected void trimForLimit()
Reduces the number of queued edits to a range of size limit, centered on the index of the next edit.
void undo()
Undoes the appropriate edits.
void undoableEditHappened(UndoableEditEvent e)
An UndoableEditListener method.
void undoOrRedo()
Convenience method that invokes one of undo or redo.
protected void undoTo(UndoableEdit edit)
Undoes all changes from the index of the next edit to edit, updating the index of the next edit appropriately.

Methods declared in class javax.swing.undo.CompoundEdit

die, getPresentationName, isInProgress, isSignificant, lastEdit

Methods declared in class javax.swing.undo.AbstractUndoableEdit

replaceEdit

Methods declared in class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Details

UndoManager

public UndoManager()
Creates a new UndoManager.

Method Details

getLimit

public int getLimit()
Returns the maximum number of edits this UndoManager holds. A value less than 0 indicates the number of edits is not limited.
Returns:
the maximum number of edits this UndoManager holds
See Also:

discardAllEdits

public void discardAllEdits()
Empties the undo manager sending each edit a die message in the process.
See Also:

trimForLimit

protected void trimForLimit()
Reduces the number of queued edits to a range of size limit, centered on the index of the next edit.

trimEdits

protected void trimEdits(int from, int to)
Removes edits in the specified range. All edits in the given range (inclusive, and in reverse order) will have die invoked on them and are removed from the list of edits. This has no effect if from > to.
Parameters:
from - the minimum index to remove
to - the maximum index to remove

setLimit

public void setLimit(int l)
Sets the maximum number of edits this UndoManager holds. A value less than 0 indicates the number of edits is not limited. If edits need to be discarded to shrink the limit, die will be invoked on them in the reverse order they were added. The default is 100.
Parameters:
l - the new limit
Throws:
RuntimeException - if this UndoManager is not in progress (end has been invoked)
See Also:

editToBeUndone

protected UndoableEdit editToBeUndone()
Returns the next significant edit to be undone if undo is invoked. This returns null if there are no edits to be undone.
Returns:
the next significant edit to be undone

editToBeRedone

protected UndoableEdit editToBeRedone()
Returns the next significant edit to be redone if redo is invoked. This returns null if there are no edits to be redone.
Returns:
the next significant edit to be redone

undoTo

protected void undoTo(UndoableEdit edit) throws CannotUndoException
Undoes all changes from the index of the next edit to edit, updating the index of the next edit appropriately.
Parameters:
edit - the edit to be undo to
Throws:
CannotUndoException - if one of the edits throws CannotUndoException

redoTo

protected void redoTo(UndoableEdit edit) throws CannotRedoException
Redoes all changes from the index of the next edit to edit, updating the index of the next edit appropriately.
Parameters:
edit - the edit to be redo to
Throws:
CannotRedoException - if one of the edits throws CannotRedoException

undoOrRedo

public void undoOrRedo() throws CannotRedoException, CannotUndoException
Convenience method that invokes one of undo or redo. If any edits have been undone (the index of the next edit is less than the length of the edits list) this invokes redo, otherwise it invokes undo.
Throws:
CannotUndoException - if one of the edits throws CannotUndoException
CannotRedoException - if one of the edits throws CannotRedoException
See Also:

canUndoOrRedo

public boolean canUndoOrRedo()
Returns true if it is possible to invoke undo or redo.
Returns:
true if invoking canUndoOrRedo is valid
See Also:

undo

public void undo() throws CannotUndoException
Undoes the appropriate edits. If end has been invoked this calls through to the superclass, otherwise this invokes undo on all edits between the index of the next edit and the last significant edit, updating the index of the next edit appropriately.
Specified by:
undo in interface UndoableEdit
Overrides:
undo in class CompoundEdit
Throws:
CannotUndoException - if one of the edits throws CannotUndoException or there are no edits to be undone
See Also:

canUndo

public boolean canUndo()
Returns true if edits may be undone. If end has been invoked, this returns the value from super. Otherwise this returns true if there are any edits to be undone (editToBeUndone returns non-null).
Specified by:
canUndo in interface UndoableEdit
Overrides:
canUndo in class CompoundEdit
Returns:
true if there are edits to be undone
See Also:

redo

public void redo() throws CannotRedoException
Redoes the appropriate edits. If end has been invoked this calls through to the superclass. Otherwise this invokes redo on all edits between the index of the next edit and the next significant edit, updating the index of the next edit appropriately.
Specified by:
redo in interface UndoableEdit
Overrides:
redo in class CompoundEdit
Throws:
CannotRedoException - if one of the edits throws CannotRedoException or there are no edits to be redone
See Also:

canRedo

public boolean canRedo()
Returns true if edits may be redone. If end has been invoked, this returns the value from super. Otherwise, this returns true if there are any edits to be redone (editToBeRedone returns non-null).
Specified by:
canRedo in interface UndoableEdit
Overrides:
canRedo in class CompoundEdit
Returns:
true if there are edits to be redone
See Also:

addEdit

public boolean addEdit(UndoableEdit anEdit)
Adds an UndoableEdit to this UndoManager, if it's possible. This removes all edits from the index of the next edit to the end of the edits list. If end has been invoked the edit is not added and false is returned. If end hasn't been invoked this returns true.
Specified by:
addEdit in interface UndoableEdit
Overrides:
addEdit in class CompoundEdit
Parameters:
anEdit - the edit to be added
Returns:
true if anEdit can be incorporated into this edit
See Also:

end

public void end()
Turns this UndoManager into a normal CompoundEdit. This removes all edits that have been undone.
Overrides:
end in class CompoundEdit
See Also:

getUndoOrRedoPresentationName

public String getUndoOrRedoPresentationName()
Convenience method that returns either getUndoPresentationName or getRedoPresentationName. If the index of the next edit equals the size of the edits list, getUndoPresentationName is returned, otherwise getRedoPresentationName is returned.
Returns:
undo or redo name

getUndoPresentationName

public String getUndoPresentationName()
Returns a description of the undoable form of this edit. If end has been invoked this calls into super. Otherwise if there are edits to be undone, this returns the value from the next significant edit that will be undone. If there are no edits to be undone and end has not been invoked this returns the value from the UIManager property "AbstractUndoableEdit.undoText".
Specified by:
getUndoPresentationName in interface UndoableEdit
Overrides:
getUndoPresentationName in class CompoundEdit
Returns:
a description of the undoable form of this edit
See Also:

getRedoPresentationName

public String getRedoPresentationName()
Returns a description of the redoable form of this edit. If end has been invoked this calls into super. Otherwise if there are edits to be redone, this returns the value from the next significant edit that will be redone. If there are no edits to be redone and end has not been invoked this returns the value from the UIManager property "AbstractUndoableEdit.redoText".
Specified by:
getRedoPresentationName in interface UndoableEdit
Overrides:
getRedoPresentationName in class CompoundEdit
Returns:
a description of the redoable form of this edit
See Also:

undoableEditHappened

public void undoableEditHappened(UndoableEditEvent e)
An UndoableEditListener method. This invokes addEdit with e.getEdit().
Specified by:
undoableEditHappened in interface UndoableEditListener
Parameters:
e - the UndoableEditEvent the UndoableEditEvent will be added from
See Also:

toString

public String toString()
Returns a string that displays and identifies this object's properties.
Overrides:
toString in class CompoundEdit
Returns:
a String representation of this object

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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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https://docs.oracle.com/en/java/javase/21/docs/api/java.desktop/javax/swing/undo/UndoManager.html