Behavioral Patterns - Memento Pattern Exercise

behavioral-patterns-memento-pattern-exercise

The Memento Pattern is used to record the internal state of an object. It is used to create a state machine and also makes undo or redo operation very easy with this pattern. In this exercise, we will use a scenario of account and account manager to understand the components of this pattern.

Reading Materials

  1. https://en.wikipedia.org/wiki/Memento_pattern (15 minutes reading)

Practice Materials

  1. Use the Memento Pattern to support an account manager to do save and roll back operations for his managed accounts.

Components:

  1. Originator (The object whose state will be saved as a memento) - Account
  2. Memento (The object that represent the saved state from its originator) - AccountMemento
  3. Caretaker (The object that keep the immutable state of mementos) - AccountManager
  4. Client (The entry point of the application that will run the given scenario) - App

Tip

  • Not all states of the originator have to be saved to a memento object.
  • To implement rollback or revert in the AccountManager, a stack could be used to keep track of the entire memento history.
  • Account.deposit or Account.withdraw could be created to change the Account.balance

Solution

Account Manager Example

Questions to discuss

  1. What are the common use cases to apply a Memento Pattern?
  2. What are the similarities and differences of the Memento Pattern and the Command Pattern?

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