javax.swing.undo

Class StateEdit

java.lang.Object

javax.swing.undo.AbstractUndoableEdit

javax.swing.undo.StateEdit

All Implemented Interfaces:

Serializable, UndoableEdit

public class StateEdit
extends AbstractUndoableEdit

A helper class, making it easy to support undo and redo.

The following example shows how to use this class.

 Foo foo; // class Foo implements StateEditable
 StateEdit edit;

 edit = new StateEdit(foo, "Name Change");
 foo.setName("Jane Doe");
 edit.end();
 undoManager.addEdit(edit);
 

If Foo’s implementation of StateEditable considers the name as part of the editable state, the user can now choose “Undo Name Change” or “Redo Name Change” from the respective menu. No further undo support is needed from the application.

The following explains what happens in the example.

1. When a StateEdit is created, the associated StateEditable gets asked to store its state into a hash table, preState.
2. The application will now perform some changes to the edited object. This typically happens by invoking methods on the edited object.
3. The editing phase is terminated by invoking the end() method of the StateEdit. The end() method does two things.
   • The edited object receives a second request for storing its state. This time, it will use a different hash table, postState.
   • To increase efficiency, the StateEdit now removes any entries from preState and postState that have the same key, and whose values are equal. Equality is determined by invoking the equals method inherited from Object.
4. When the user later chooses to undo the StateEdit, the edited object is asked to restore its state from the preState table. Similarly, when the user chooses to redo the StateEdit, the edited object gets asked to restore its state from the postState.

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
protected StateEditable	object The object which is being edited by this StateEdit.
protected Hashtable<Object,Object>	postState The state of object at the time when end() was called.
protected Hashtable<Object,Object>	preState The state of object at the time of constructing this StateEdit.
protected static String	RCSID The ID of the Java source file in Sun’s Revision Control System (RCS).
protected String	undoRedoName A human-readable name for this edit action.

Fields inherited from class javax.swing.undo.AbstractUndoableEdit

RedoName, UndoName

Constructor Summary

Constructors

Constructor and Description
StateEdit(StateEditable obj) Constructs a StateEdit, specifying the object whose state is being edited.
StateEdit(StateEditable obj, String name) Constructs a StateEdit, specifying the object whose state is being edited.

Method Summary

Methods

Modifier and Type	Method and Description
void	end() Informs this StateEdit that all edits are finished.
String	getPresentationName() Returns a human-readable, localized name that describes this editing action and can be displayed to the user.
protected void	init(StateEditable obj, String name) Initializes this StateEdit.
void	redo() Redoes this edit operation.
protected void	removeRedundantState() Removes all redundant entries from the pre- and post-edit state hash tables.
void	undo() Undoes this edit operation.

Methods inherited from class javax.swing.undo.AbstractUndoableEdit

addEdit, canRedo, canUndo, die, getRedoPresentationName, getUndoPresentationName, isSignificant, replaceEdit, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

RCSID

protected static final String RCSID

The ID of the Java source file in Sun’s Revision Control System (RCS). This certainly should not be part of the API specification. But in order to be API-compatible with Sun’s reference implementation, GNU Classpath also has to provide this field and match its value. The value used here has been in every JDK release at least from 1.2 to 1.5.

See Also:

Constant Field Values

object

protected StateEditable object

The object which is being edited by this StateEdit.

preState

protected Hashtable<Object,Object> preState

The state of object at the time of constructing this StateEdit.

postState

protected Hashtable<Object,Object> postState

The state of object at the time when end() was called.

undoRedoName

protected String undoRedoName

A human-readable name for this edit action.

Constructor Detail

StateEdit

public StateEdit(StateEditable obj)

Constructs a StateEdit, specifying the object whose state is being edited.

Parameters:

obj - the object whose state is being edited by this StateEdit.

StateEdit

public StateEdit(StateEditable obj,
         String name)

Constructs a StateEdit, specifying the object whose state is being edited.

Parameters:

obj - the object whose state is being edited by this StateEdit.

name - the human-readable name of the editing action.

Method Detail

init

protected void init(StateEditable obj,
        String name)

Initializes this StateEdit. The edited object will be asked to store its current state into preState.

Parameters:

obj - the object being edited.

name - the human-readable name of the editing action.

end

public void end()

Informs this StateEdit that all edits are finished. The edited object will be asked to store its state into postState, and any redundant entries will get removed from preState and postState.

undo

public void undo()

Undoes this edit operation. The edited object will be asked to restore its state from preState.

Specified by:

undo in interface UndoableEdit

Overrides:

undo in class AbstractUndoableEdit

Throws:

CannotUndoException - if AbstractUndoableEdit.canUndo() returns false, for example because this action has already been undone.

See Also:

AbstractUndoableEdit.canUndo(), AbstractUndoableEdit.redo()

redo

public void redo()

Redoes this edit operation. The edited object will be asked to restore its state from postState.

Specified by:

redo in interface UndoableEdit

Overrides:

redo in class AbstractUndoableEdit

Throws:

CannotRedoException - if AbstractUndoableEdit.canRedo() returns false, for example because this action has not yet been undone.

See Also:

AbstractUndoableEdit.canRedo(), AbstractUndoableEdit.undo()

getPresentationName

public String getPresentationName()

Returns a human-readable, localized name that describes this editing action and can be displayed to the user.

Specified by:

getPresentationName in interface UndoableEdit

Overrides:

getPresentationName in class AbstractUndoableEdit

Returns:

the name, or null if no presentation name is available.

removeRedundantState

protected void removeRedundantState()

Removes all redundant entries from the pre- and post-edit state hash tables. An entry is considered redundant if it is present both before and after the edit, and if the two values are equal.