Memento

Question 1

Intent

Answer 1

Without breaking encapsulation, capture and externalize an object’s internal state.

Question 2

Motivation

Answer 2

Store a snapshot of the internal state of another object, originator

Question 3

Structure

Answer 3

Question 4

Participants

Answer 4

• Memento
  
  • stores the internal state of the Originator
  • Mementos have two interfaces: narrow interface (Caretaker) and wide interface (Originator)
• Originator
  
  • creates a memento containing a snapshot of its current internal state
  • uses the memento to restore its internal state
• Caretaker
  
  • responsible for the memento’s safekeeping
  • never examines or operates on the contents of memento

Question 5

Related Patterns

Answer 5

• Command
• Iterator

Question 6

Collaborations

Answer 6

Caretaker (client) can request a memento from the originator (to save a snapshot) and pass a memento back to the originator (to restore previous state)

Question 7

AKA

Answer 7

Token

Question 8

What is the role of a Caretaker

Answer 8

Setting and getting the memento.

Question 9

Does the Caretaker have access to the contents of a memento?

Answer 9

No

Question 10

Which participant stores the internal state of which object?

Answer 10

Memento stores the internal state of Originator.

Question 11

Mementos have two interfaces, narrow and wide. Which participants are what?

Answer 11

• Originator* is wide interface.
• Caretaker* is narrow interface.