Module java.desktop
Package javax.swing.undo

Class 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.

    • Constructor Detail

      • UndoManager

        public UndoManager()
        Creates a new UndoManager.

    • Method Detail

      • 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 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

      • 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()

      • 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()

      • 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()

      • 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