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 JavaBeansTM
has been added to the java.beans package.
Please see
java.beans.XMLEncoder .
author:
Ray Ryan
version:
1.45, 05/05/07 | 