Class UndoManager

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

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

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

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

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.

Constructors

UndoManager

public UndoManager()

Creates a new UndoManager.

Methods

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:

addEdit(javax.swing.undo.UndoableEdit), setLimit(int)

discardAllEdits

public void discardAllEdits()

Empties the undo manager sending each edit a die message in the process.

See Also:

AbstractUndoableEdit.die()

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:

CompoundEdit.isInProgress(), end(), addEdit(javax.swing.undo.UndoableEdit), getLimit()

editToBeUndone

protected UndoableEdit editToBeUndone()

Returns the 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 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.

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.

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(), getUndoOrRedoPresentationName()

canUndoOrRedo

public boolean canUndoOrRedo()

Returns true if it is possible to invoke undo or redo.

Returns:

true if invoking canUndoOrRedo is valid

See Also:

undoOrRedo()

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:

CompoundEdit.end(), canUndo(), editToBeUndone()

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:

CompoundEdit.canUndo(), editToBeUndone()

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:

CompoundEdit.end(), canRedo(), editToBeRedone()

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:

CompoundEdit.canRedo(), editToBeRedone()

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:

CompoundEdit.end(), CompoundEdit.addEdit(javax.swing.undo.UndoableEdit)

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:

CompoundEdit.end()

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:

undo(), CompoundEdit.getUndoPresentationName()

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:

redo(), CompoundEdit.getRedoPresentationName()

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:

addEdit(javax.swing.undo.UndoableEdit)

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