Memento pattern in LLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main purpose of the Memento pattern?

The Memento pattern helps save and restore an object's state without exposing its internal details. It allows undo or rollback operations safely.

beginner

Which three roles are involved in the Memento pattern?

1. Originator: The object whose state is saved.<br>2. Memento: Stores the saved state.<br>3. Caretaker: Manages mementos but does not modify them.

intermediate

Why should the Memento hide its state from other objects except the Originator?

To protect encapsulation and prevent other objects from changing the saved state directly, ensuring data integrity.

intermediate

How does the Caretaker interact with the Memento in the pattern?

The Caretaker requests a Memento from the Originator to save state and later gives the Memento back to restore state, but it never changes the Memento's content.

beginner

Give a real-life example that illustrates the Memento pattern.

Think of a text editor with an undo feature. The editor saves snapshots of the document (Mementos). When you undo, it restores the document to a previous snapshot without exposing how the document stores data internally.

Which component in the Memento pattern is responsible for creating a snapshot of the object's state?

A Originator

B Caretaker

C Memento

D Client

The Originator creates a Memento that stores its current state.

What is the role of the Caretaker in the Memento pattern?

A Store and manage Mementos without changing them

B Modify the saved state

C Create Mementos

D Restore the Originator's state directly

The Caretaker keeps Mementos safe but does not modify their content.

Why is it important that the Memento pattern preserves encapsulation?

A To allow other objects to change the state

B To avoid saving the state

C To hide the internal state from all except the Originator

D To make the state public

Encapsulation ensures only the Originator can access and restore its state.

Which scenario best fits the use of the Memento pattern?

A Logging user actions

B Undo functionality in an application

C Sharing data between objects

D Encrypting data

Undo requires saving and restoring previous states, which Memento supports.

In the Memento pattern, who is responsible for restoring the saved state?

A Memento

B Client

C Caretaker

D Originator

The Originator uses the Memento to restore its own state.

Explain the roles and responsibilities of the Originator, Memento, and Caretaker in the Memento pattern.

Think about who saves, who holds, and who restores the state.

Describe a real-world example where the Memento pattern can be applied and explain why it fits.

Consider common software features that let you go back to a previous state.