Behavioural Design Pattern: Memento Design pattern

Define the Memento Design pattern

This technique is used to capture an object's present state and store it in a way that allows it to be restored later without violating the encapsulation restrictions.

Examples of Memento Patterns

Examples of memento patterns include:

• Undo Operation
• Transaction Rollback

Memento Pattern with UML diagram

The classes, interfaces, and objects in the above UML class diagram are defined as follows.

• Originator: This class generates a memento object providing a snapshot of the originator's current state. It also resets the Originator to a previously saved state using the SetMemento procedure.
• Memento: This class contains information about the originator's preserved state.
• Caretaker: This class is used to store Memento objects for later use. This merely serves as a storage; it never examines or modifies the contents of the Memento object.

When Should You Use the Memento Design Pattern?

The memento design pattern is important in the following scenarios:

• An object's state must be saved and restored later.
• It cannot be accessible directly through an interface without revealing implementation.

Advantages of the Memento Design Pattern

• Undo Mechanism: Provides an undo mechanism by storing the object's previous state.
• Preserving Encapsulation: Because only the originator can store and retrieve information from the memento, the encapsulation is not violated.
• Ease of Restoration: The originator can return the state to an earlier point in time.