java-design-patterns/memento/README.md

---
layout: pattern
title: Memento
folder: memento
permalink: /patterns/memento/
categories: Behavioral
tags:
 - Gang of Four
---

## Also known as
Token

## Intent
Without violating encapsulation, capture and externalize an
object's internal state so that the object can be restored to this state later.

## Class diagram
![alt text](./etc/memento.png "Memento")

## Applicability
Use the Memento pattern when

* a snapshot of an object's state must be saved so that it can be restored to that state later, and
* a direct interface to obtaining the state would expose implementation details and break the object's encapsulation

## Real world examples

* [java.util.Date](http://docs.oracle.com/javase/8/docs/api/java/util/Date.html)

## Credits

* [Design Patterns: Elements of Reusable Object-Oriented Software](https://www.amazon.com/gp/product/0201633612/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0201633612&linkCode=as2&tag=javadesignpat-20&linkId=675d49790ce11db99d90bde47f1aeb59)
* [Head First Design Patterns: A Brain-Friendly Guide](https://www.amazon.com/gp/product/0596007124/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0596007124&linkCode=as2&tag=javadesignpat-20&linkId=6b8b6eea86021af6c8e3cd3fc382cb5b)
Work towards #56: Splitting up the README I did the job and splitted up the readme, hopefully everything was splitted correctly... 2015-08-13 23:54:40 +02:00			`---`
			`layout: pattern`
			`title: Memento`
			`folder: memento`
Work towards #56: Add permalink to every pattern This makes cleaner URLs thanks to jekyll 2015-08-15 18:03:05 +02:00			`permalink: /patterns/memento/`
Work on #213 - properly categorize all patterns - remove pattern list from readme - minor fixes to readme - removed "introduction" because its not a pattern and an error i committed some time ago 2015-08-20 21:40:07 +02:00			`categories: Behavioral`
Work on #226, #213, added references of Gang Of Four to all GoF patterns, added tag for Gang Of Four, added difficulty tags to some of them 2015-09-22 18:25:56 +05:30			`tags:`
https://github.com/iluwatar/java-design-patterns-web/issues/8 Fix typo in tag 2019-12-13 22:22:11 +02:00			`- Gang of Four`
Work towards #56: Splitting up the README I did the job and splitted up the readme, hopefully everything was splitted correctly... 2015-08-13 23:54:40 +02:00			`---`

Use headings instead of bold text in index.md #238 2016-01-03 21:14:30 +01:00			`## Also known as`
			`Token`
Added alias names for GOF patterns #267 2015-11-04 21:13:32 +02:00
Use headings instead of bold text in index.md #238 2016-01-03 21:14:30 +01:00			`## Intent`
			`Without violating encapsulation, capture and externalize an`
Work towards #56: Splitting up the README I did the job and splitted up the readme, hopefully everything was splitted correctly... 2015-08-13 23:54:40 +02:00			`object's internal state so that the object can be restored to this state later.`

#1113 Link uml-reverse-mapper created class diagrams to readme, where needed 2019-12-07 20:01:13 +02:00			`## Class diagram`
Work towards #56: Splitting up the README I did the job and splitted up the readme, hopefully everything was splitted correctly... 2015-08-13 23:54:40 +02:00			`![alt text](./etc/memento.png "Memento")`

Use headings instead of bold text in index.md #238 2016-01-03 21:14:30 +01:00			`## Applicability`
			`Use the Memento pattern when`
Work towards #56: Splitting up the README I did the job and splitted up the readme, hopefully everything was splitted correctly... 2015-08-13 23:54:40 +02:00
			`* a snapshot of an object's state must be saved so that it can be restored to that state later, and`
			`* a direct interface to obtaining the state would expose implementation details and break the object's encapsulation`

Use headings instead of bold text in index.md #238 2016-01-03 21:14:30 +01:00			`## Real world examples`
Work towards #56: Splitting up the README I did the job and splitted up the readme, hopefully everything was splitted correctly... 2015-08-13 23:54:40 +02:00
Work towards #56: Add permalink to every pattern This makes cleaner URLs thanks to jekyll 2015-08-15 18:03:05 +02:00			`* [java.util.Date](http://docs.oracle.com/javase/8/docs/api/java/util/Date.html)`
Work on #226, #213, added references of Gang Of Four to all GoF patterns, added tag for Gang Of Four, added difficulty tags to some of them 2015-09-22 18:25:56 +05:30
Use headings instead of bold text in index.md #238 2016-01-03 21:14:30 +01:00			`## Credits`
Work on #226, #213, added references of Gang Of Four to all GoF patterns, added tag for Gang Of Four, added difficulty tags to some of them 2015-09-22 18:25:56 +05:30
Update links 2020-07-06 13:31:07 +03:00			`* [Design Patterns: Elements of Reusable Object-Oriented Software](https://www.amazon.com/gp/product/0201633612/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0201633612&linkCode=as2&tag=javadesignpat-20&linkId=675d49790ce11db99d90bde47f1aeb59)`
Add links to Head First Design Patterns book 2020-07-07 18:05:11 +03:00			`* [Head First Design Patterns: A Brain-Friendly Guide](https://www.amazon.com/gp/product/0596007124/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0596007124&linkCode=as2&tag=javadesignpat-20&linkId=6b8b6eea86021af6c8e3cd3fc382cb5b)`