Java Swing, 2nd Edition

The Swing Undo Facility

The javax.swing.undo package contains two interfaces and seven classes (two of which are exception classes). These, along with a listener interface and event class from the javax.swing.event package, comprise the undo facility shown in Figure 18-1.

Figure 18-1. The Swing undo facility

Here is a brief overview of each class:

UndoableEdit

The base interface for just about everything else in the undo package. It serves as an abstraction for anything in an application that can be undone.

AbstractUndoableEdit

The default implementation of UndoableEdit provides a starting point for building new UndoableEdit classes. It provides a simple set of rules for determining whether undo and redo requests are allowable (based on whether the edit has already been undone, redone, or killed). Despite its name, it is not an abstract class. This is really just a technicality since the default implementation is not at all useful as it is, so you’d never want to instantiate one.

CompoundEdit

This extension of AbstractUndoableEdit allows multiple edits to be grouped together into a single edit. Those familiar with the classic Design Patterns by Erich Gamma et al. (Addison-Wesley) will recognize this construct as a basic implementation of the Composite pattern.

UndoableEditEvent

This event class can be used to notify listeners that an undoable edit has been made.

UndoableEditListener ...