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Memento

Memento. Alex “J Lo” Brian C Kiefer. Definitions. A Memento is a way to create an object that previously existed a tiny repository that saves an object’s state. Challenge 19.1. What a few reasons that you might choose to saving a memento in a file rather than as an object?. Challenge 19.1.

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Memento

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  1. Memento Alex “J Lo” Brian C Kiefer

  2. Definitions • A Memento is • a way to create an object that previously existed • a tiny repository that saves an object’s state

  3. Challenge 19.1 • What a few reasons that you might choose to saving a memento in a file rather than as an object?

  4. Challenge 19.1 • What a few reasons that you might choose to saving a memento in a file rather than as an object? • The ability to restore an object’s state has to survive a system crash. • You anticipate that the user will exit the system and will want to resume work later. • You need to reconstruct an object on another computer.

  5. Applications of Memento • Undo • Your favorite feature • Persistent Storage • String output

  6. Challenge • What is the best data structure to use for Undo?

  7. Challenge • What is the best data structure to use for Undo? • Stack

  8. Challenge • What is the best data structure to use for Undo? • Stack • How can Java assist you in using Memento for persistent storage?

  9. Challenge • What is the best data structure to use for Undo? • Stack • How can Java assist you in using Memento for persistent storage? • Serialization • XML parsing

  10. Challenge 19.5 • What are the disadvantages of storing an object as text?

  11. Challenge 19.5 • What are the disadvantages of storing an object as text? • Encapsulation flies out the window. Anyone with a text editor can manipulate the object’s data. • For this approach to work, you must be able to parse the text, either using XML parser or writing your own parser for a proprietary format. • A textual representation may be much larger than an object serialization with the same information.

  12. Challenge 19.5b • What are the advantages of storing an object as text?

  13. Challenge 19.5b • What are the advantages of storing an object as text? • Anyone with a text editor can verify an object’s data. • Anyone with a text editor can manipulate an object’s data—an advantage in some contexts. • It is often easier to pass text between systems than it is to setup interchange with RMI, CORBA, or other protocols.

  14. Summary • Used for undo and redo • Forward and Back buttons • Can be used for saving files • Via serialization • Via strings

  15. Can’t remember something? Questions? Comments?

  16. Exercise Console browser, without browsing… • Implement a back command • Implement a forward command • Implement saving session to disk See demo program and problem explanation at http://www.alexlo.net/patterns/

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