Static Class Structure

• Caretaker
  • Refers to the Originator class to save and restore originator's internal state.
  • Holds Memento objects, created and returned by the originator, and passes back a memento to the originator to restore to a previous state.
  • Isn't permitted to access a Memento object.
• Originator
  • Defines an operation (createMemento()) for saving its current internal state to a Memento object.
  • Defines an operation (restore(memento)) for restoring to a previous state from a passed in Memento object.
• Memento
  • Stores an originator's internal state.
  • Only the originator that created a memento can access it.
  • This is usually implemented by making memento an inner class of originator and declaring all members of memento private.
  • See also Implementation and Sample Code.

Dynamic Object Collaboration

• This sample scenario shows (1) saving and (2) restoring the internal state of an Originator object.
• (1) To save the Originator's current internal state, the Caretaker calls createMemento() on the Originator.
• The Originator creates a new Memento object, saves its current internal state (setState()), and returns the Memento object to the Caretaker.
• The Caretaker holds (takes care of) the returned Memento object(s).
• (2) To restore the Originator to a previous state, the Caretaker calls restore(memento) on the Originator by providing the Memento object to be restored.
• The Originator gets the state to be restored from the provided Memento object (getState()).
• See also Sample Code / Example1.