Memento Pattern
Author: Deron Eriksson
Description: This Java tutorial describes the memento pattern, a behavioral object pattern.
Tutorial created using: Windows Vista || JDK 1.6.0_11 || Eclipse JEE Ganymede SR1 (Eclipse 3.4.1)

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The MementoDemo class demonstrates the memento pattern. It creates a caretaker and then a DietInfo object. The DietInfo object's state is changed and displayed. At one point, the caretaker saves the state of the DietInfo object. After this, the DietInfo object's state is further changed and displayed. After this, the caretaker restores the state of the DietInfo object. We verify this restoration by displaying the DietInfo object's state.

package com.cakes;

public class MementoDemo {

	public static void main(String[] args) {

		// caretaker
		DietInfoCaretaker dietInfoCaretaker = new DietInfoCaretaker();

		// originator
		DietInfo dietInfo = new DietInfo("Fred", 1, 100);

		dietInfo.setDayNumberAndWeight(2, 99);

		System.out.println("Saving state.");

		dietInfo.setDayNumberAndWeight(3, 98);

		dietInfo.setDayNumberAndWeight(4, 97);

		System.out.println("Restoring saved state.");



The console output of the execution of MementoDemo is shown here. Notice how the state changes, and how we are able to save and restore the state of the originator via the caretaker's reference to the memento.

Console Output

Name: Fred, day number: 1, weight: 100
Name: Fred, day number: 2, weight: 99
Saving state.
Name: Fred, day number: 3, weight: 98
Name: Fred, day number: 4, weight: 97
Restoring saved state.
Name: Fred, day number: 2, weight: 99
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