📅Week 8 (Day-4) - System Design: Exploring the Memento Design Pattern with UML and Coding

NOTE: - I started my 8-week system design journey with Coder Army. I will be journaling every day, recording what I learn, reflecting on it, and sharing it with my network to help newcomers to system design.

Namaste Developers!

Welcome to another exciting day of the #8WeeksLLDChallenge — and today, we’re diving into a powerful design pattern that helps you preserve and restore object states like a pro: the Memento Design Pattern.

💠What is the Memento Pattern?

Provides the ability to take snapshots of an object at various points in time and enables undo capabilities to revert to a previous state.

The Memento Pattern provides the ability to save and restore an object’s state without violating its encapsulation. Think of it as clicking a "Save Point" in a game so you can load it later!

(Hindi: Memento Pattern humein kisi bhi object ka snapshot lene ki ability deta hai bina uske internal data ko tod-phod kiye. Ek tarah ka screenshot leke future mein use wapas restore karne ka tareeka hai.)

💠Structure of the Pattern

1. Originator: The one whose state we want to save

   (Object jiska state hum save karte hain).

2. Memento: Stores the internal state

   (State ko store karne wala object).

3. Caretaker: Handles the saved states but doesn't modify them

   (Mementos ko store aur manage karta hai , like a caretaker of backups).

   💠Real-World Analogy

   📍Git: Jab hum commit karte hain, it saves a snapshot of our code — so we can go back to that version if needed.

   📍 Database Transactions: Update karne se pehle backup lete hain, so that we can rollback if something goes wrong.

   📍 MS Word Undo: Every time you type something, you can go back to the previous state using CTRL + Z — jaise har action ka ek snapshot save ho raha ho.

💠UML

💠Practical Example - Simple In-Memory Database

Problem: We want to support undo/rollback in a mini database.

Roles:

• Originator: Database class

• Memento: DatabaseMemento class

• Caretaker: TransactionManager

💠Code

Database db = new Database();
TransactionManager tm = new TransactionManager();

db.create("user1", "Payal");
tm.beginTxn(db); // Save snapshot

db.update("user1", "Kumari");
tm.rollback(db); // Revert to old state

💠Why use Memento?

✅ Backup & Undo support

✅ Encapsulation safe

✅ Easy to manage historical states

💠When to Use?

• Word processors (undo)

• Drawing apps (revert changes)

• Games (save checkpoints)

• Database systems (transactions/rollback)

💠Summary

💠Conclusion

Memento pattern bohot powerful hai jab bhi aapko backup ya undo functionality chahiye. Yeh pattern aapko state save karne ki full flexibility deta hai without breaking rules of encapsulation.

(Hindi: Agar aapka system me "Ctrl + Z" type ka feature banana hai, toh Memento Pattern is the hero! )

💠Final Thoughts

Week - 8 (Day-4) Completed ✅ System Design

NOTE : - A big thanks to my mentors Rohit Negi Sir and Aditya Sir for launching this amazing 8-week course absolutely free on YouTube via CoderArmy9 :- youtube.com/@CoderArmy9 . 🙌

👉 Share this blog with your connections! Let’s keep learning, growing, and supporting one another on this journey. 🚀

✍️ Payal Kumari 👩‍💻

Jai Hind 🇮🇳 | #CoderArmy #LearningInPublic #SystemDesign #TechForAll #MentorshipMatters #8weeksLLdChallenge #LowLevelDesign #LLD 👩‍💻