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Memento

Memento. Kendra Kachelein Maureen Thomas. Definition. The memento captures and externalizes an object’s internal state, so the object can be restored to that state later. Applicability. Use the Memento pattern when:

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Memento

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  1. Memento Kendra Kachelein Maureen Thomas

  2. Definition • The memento captures and externalizes an object’s internal state, so the object can be restored to that state later.

  3. Applicability • Use the Memento pattern when: • A snapshot of an object’s state must be saved so that it can be restore to that state later, and • A direct interface to obtaining the state would expose implementation details and break the object’s encapsulation

  4. Participants • There are 3 participants in the Memento pattern: • Originator: whose state has to be maintained • Memento: stores the state of the Originator object • Caretaker: has a handle to the Memento

  5. Example 34-55-09 Caretaker Memento Originator

  6. UML Diagram Caretaker Originator Memento -State -State +GetState() +SetState() +SetMemento(in Memento) +CreateMemento() Class Example: Security Guard Owner Safety Deposit -State -State +GetCombo() +GiveCombo() +DepositCombination(in Memento) +WriteCombination()

  7. Source Code Implementation public class Owner { private int combination public safetyDeposit getCombo() { return new saftetyDeposit(this); } public void giveCombo(safetyDeposit sd) { combination = sd.combination; }

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