public UndoManager() 
{
        super();
        indexOfNextAdd = 0;
        limit = 100;
        edits.ensureCapacity(limit);
}

Creates a new UndoManager.

 public synchronized boolean addEdit(UndoableEdit anEdit) 
{
        boolean retVal;
        // Trim from the indexOfNextAdd to the end, as we'll
        // never reach these edits once the new one is added.
        trimEdits(indexOfNextAdd, edits.size()-1);
        retVal = super.addEdit(anEdit);
        if (inProgress) {
          retVal = true;
        }
        // Maybe super added this edit, maybe it didn't (perhaps
        // an in progress compound edit took it instead. Or perhaps
        // this UndoManager is no longer in progress). So make sure
        // the indexOfNextAdd is pointed at the right place.
        indexOfNextAdd = edits.size();
        // Enforce the limit
        trimForLimit();
        return retVal;
}

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.

 public synchronized boolean canRedo() 
{
        if (inProgress) {
            UndoableEdit edit = editToBeRedone();
            return edit != null && edit.canRedo();
        } else {
            return super.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).

 public synchronized boolean canUndo() 
{
        if (inProgress) {
            UndoableEdit edit = editToBeUndone();
            return edit != null && edit.canUndo();
        } else {
            return super.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).

 public synchronized boolean canUndoOrRedo() 
{
        if (indexOfNextAdd == edits.size()) {
            return canUndo();
        } else {
            return canRedo();
        }
}

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

 public synchronized  void discardAllEdits() 
{
        for (UndoableEdit e : edits) {
            e.die();
        }
        edits = new Vector< UndoableEdit >();
        indexOfNextAdd = 0;
        // PENDING(rjrjr) when vector grows a removeRange() method
        // (expected in JDK 1.2), trimEdits() will be nice and
        // efficient, and this method can call that instead.
}

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

 protected UndoableEdit editToBeRedone() 
{
        int count = edits.size();
        int i = indexOfNextAdd;
        while (i <  count) {
            UndoableEdit edit = edits.elementAt(i++);
            if (edit.isSignificant()) {
                return edit;
            }
        }
        return null;
}

Returns the the next significant edit to be redone if redo is invoked. This returns null if there are no edits to be redone.

 protected UndoableEdit editToBeUndone() 
{
        int i = indexOfNextAdd;
        while (i  > 0) {
            UndoableEdit edit = edits.elementAt(--i);
            if (edit.isSignificant()) {
                return edit;
            }
        }
        return null;
}

Returns the the next significant edit to be undone if undo is invoked. This returns null if there are no edits to be undone.

 public synchronized  void end() 
{
        super.end();
        this.trimEdits(indexOfNextAdd, edits.size()-1);
}

Turns this UndoManager into a normal CompoundEdit. This removes all edits that have been undone.

 public synchronized int getLimit() 
{
        return limit;
}

Returns the maximum number of edits this {@code UndoManager} holds. A value less than 0 indicates the number of edits is not limited.

 public synchronized String getRedoPresentationName() 
{
        if (inProgress) {
            if (canRedo()) {
                return editToBeRedone().getRedoPresentationName();
            } else {
                return UIManager.getString("AbstractUndoableEdit.redoText");
            }
        } else {
            return super.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".

 public synchronized String getUndoOrRedoPresentationName() 
{
        if (indexOfNextAdd == edits.size()) {
            return getUndoPresentationName();
        } else {
            return getRedoPresentationName();
        }
}

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.

 public synchronized String getUndoPresentationName() 
{
        if (inProgress) {
            if (canUndo()) {
                return editToBeUndone().getUndoPresentationName();
            } else {
                return UIManager.getString("AbstractUndoableEdit.undoText");
            }
        } else {
            return super.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".

 public synchronized  void redo() throws CannotRedoException 
{
        if (inProgress) {
            UndoableEdit edit = editToBeRedone();
            if (edit == null) {
                throw new CannotRedoException();
            }
            redoTo(edit);
        } else {
            super.redo();
        }
}

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.

 protected  void redoTo(UndoableEdit edit) throws CannotRedoException 
{
        boolean done = false;
        while (!done) {
            UndoableEdit next = edits.elementAt(indexOfNextAdd++);
            next.redo();
            done = next == edit;
        }
}

Redoes all changes from the index of the next edit to edit, updating the index of the next edit appropriately.

 public synchronized  void setLimit(int l) 
{
        if (!inProgress) throw new RuntimeException("Attempt to call UndoManager.setLimit() after UndoManager.end() has been called");
        limit = l;
        trimForLimit();
}

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.

 public String toString() 
{
        return super.toString() + " limit: " + limit +
            " indexOfNextAdd: " + indexOfNextAdd;
}

Returns a string that displays and identifies this object's properties.

 protected  void trimEdits(int from,
    int to) 
{
        if (from < = to) {
//          System.out.println("Trimming " + from + " " + to + " with index " +
//                           indexOfNextAdd);
            for (int i = to; from < = i; i--) {
                UndoableEdit e = edits.elementAt(i);
//              System.out.println("JUM: Discarding " +
//                                 e.getUndoPresentationName());
                e.die();
                // PENDING(rjrjr) when Vector supports range deletion (JDK
                // 1.2) , we can optimize the next line considerably.
                edits.removeElementAt(i);
            }
            if (indexOfNextAdd  > to) {
//              System.out.print("...right...");
                indexOfNextAdd -= to-from+1;
            } else if (indexOfNextAdd  >= from) {
//              System.out.println("...mid...");
                indexOfNextAdd = from;
            }
//          System.out.println("new index " + indexOfNextAdd);
        }
}

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.

 protected  void trimForLimit() 
{
        if (limit  >= 0) {
            int size = edits.size();
//          System.out.print("limit: " + limit +
//                           " size: " + size +
//                           " indexOfNextAdd: " + indexOfNextAdd +
//                           "\n");
            if (size  > limit) {
                int halfLimit = limit/2;
                int keepFrom = indexOfNextAdd - 1 - halfLimit;
                int keepTo   = indexOfNextAdd - 1 + halfLimit;
                // These are ints we're playing with, so dividing by two
                // rounds down for odd numbers, so make sure the limit was
                // honored properly. Note that the keep range is
                // inclusive.
                if (keepTo - keepFrom + 1  > limit) {
                    keepFrom++;
                }
                // The keep range is centered on indexOfNextAdd,
                // but odds are good that the actual edits Vector
                // isn't. Move the keep range to keep it legal.
                if (keepFrom <  0) {
                    keepTo -= keepFrom;
                    keepFrom = 0;
                }
                if (keepTo  >= size) {
                    int delta = size - keepTo - 1;
                    keepTo += delta;
                    keepFrom += delta;
                }
//              System.out.println("Keeping " + keepFrom + " " + keepTo);
                trimEdits(keepTo+1, size-1);
                trimEdits(0, keepFrom-1);
            }
        }
}

Reduces the number of queued edits to a range of size limit, centered on the index of the next edit.

 public synchronized  void undo() throws CannotUndoException 
{
        if (inProgress) {
            UndoableEdit edit = editToBeUndone();
            if (edit == null) {
                throw new CannotUndoException();
            }
            undoTo(edit);
        } else {
            super.undo();
        }
}

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.

 public synchronized  void undoOrRedo() throws CannotRedoException, CannotUndoException 
{
        if (indexOfNextAdd == edits.size()) {
            undo();
        } else {
            redo();
        }
}

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.

 protected  void undoTo(UndoableEdit edit) throws CannotUndoException 
{
        boolean done = false;
        while (!done) {
            UndoableEdit next = edits.elementAt(--indexOfNextAdd);
            next.undo();
            done = next == edit;
        }
}

Undoes all changes from the index of the next edit to edit, updating the index of the next edit appropriately.

 public  void undoableEditHappened(UndoableEditEvent e) 
{
        addEdit(e.getEdit());
}

An UndoableEditListener method. This invokes addEdit with e.getEdit().