Memento

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Memento

• Kendra Kachelein
• Maureen Thomas

2
Definition

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

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Applicability

• Use the Memento pattern when
• A snapshot of an objects 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
  objects encapsulation

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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

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Example
34-55-09
Caretaker
Memento
Originator
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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(
)
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Source Code Implementation

• public class Owner
• private int combination
• public safetyDeposit getCombo()
• return new saftetyDeposit(this)
• public void giveCombo(safetyDeposit sd)
• combination sd.combination