Intent
To record an object internal state without violating encapsulation and reclaim it later without knowledge of the original object.
Where to use & benefits
- Let some info in an object to be available by another object by using default access control.
- Save some info for later uses.
- Need undo/redo features.
- Used in database transaction.
Structure
Participants
Memento (Memento)
stores internal state of the Originator object. The memento may store as much or as little of the originator's internal state as necessary at its originator's discretion.
Originator (Not used)
creates a memento containing a snapshot of its current internal state and uses the memento to restore its internal state
Caretaker (MainApplet)
is responsible for the memento's safekeeping and never operates on or examines the contents of a memento.
Example
In the demonstration application, the Memento class is used by the MainApplet for the undo operation (specifically for shape creation).
Class Diagram
