Persisting Mementos Across Sessions

A session occurs when a user runs a program, conducts transactions in the program, and exits. Suppose that your users want to be able to save a simulation in one session and restore it in another session. This ability is a matter normally referred to as persistent storage. Persistent storage fulfills the intent of the MEMENTO pattern and is a natural extension to the undo functionality you have already implemented.

Suppose that you subclass the Visualization class with a Visualization2 class that has a menu bar with a File menu with Save As... and Restore From... items: