Class StateEdit

The following example shows how to use this class.

 Foo foo; // class Foo implements {@link StateEditable}
 StateEdit edit;

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

If Foo’s implementation of {@link 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 {@link StateEditable} gets asked to store its state into a hash table, {@link #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 {@link #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, {@link #postState}.
   • To increase efficiency, the StateEdit now removes any entries from {@link #preState} and {@link #postState} that have the same key, and whose values are equal. Equality is determined by invoking the equals method inherited from {@link java.lang.Object}.
4. When the user later chooses to undo the StateEdit, the edited object is asked to {@linkplain StateEditable#restoreState restore its state} from the {@link #preState} table. Similarly, when the user chooses to redo the StateEdit, the edited object gets asked to restore its state from the {@link #postState}.