System Design Full Course - Build Payment Gateway System | System Design

Welcome to Lecture 23 of the Ultimate Low-Level Design (LLD) Series by Coder Army! fifth week for #lowleveldesign #systemdesign #8weeksLLdchallenge. We are doing 8 weeks challenge and going to complete the whole course within the duration with quality content on Youtube. Let’s learn LLD like never before and attain advance level mastery on this subject. In this lecture, we’ll design and implement a *Payment Gateway System* from scratch using Low-Level Design principles in C++ & Java. You’ll see how to combine multiple design patterns—Strategy, Template Method, Proxy, Factory, and Singleton—to create a robust, extensible, and maintainable architecture. *What You’ll Learn:* - *Strategy Pattern* for pluggable banking systems (Paytm, Razorpay) - *Template Method Pattern* to define the payment workflow skeleton - *Proxy Pattern* to add retry logic transparently - *Factory & Singleton Patterns* for gateway creation and global access - How the *Controller* orchestrates requests end-to-end - *UML Diagrams* & live coding walkthrough in C++ By the end of this video, you'll understand how to decompose a complex system into clean, pattern-driven components—and you’ll be able to apply these principles to any real-world project. Join Coder Army Whatsapp Group: https://whatsapp.com/channel/0029Va6H0tbHVvTbcuT99Y1f Code and Notes: Github : https://github.com/adityatandon15/LLD Connect with Aditya Tandon Instagram : https://www.instagram.com/adityatandon2 LinkedIn : https://www.linkedin.com/in/adityatandon2 Twitter : https://x.com/adityatandon02 00:00 Introduction 01:28 Requirements Analysis 07:08 Happy Flow 09:14 What is Payment gateway 12:31 Back to Flow Discussion 13:25 UML Design 44:19 Code for Payment Gateway 58:21 Further Enhancements #SystemDesign #LowLevelDesign #LLD #AdapterPattern #DesignPatterns #Cplusplus #JavaDevelopers #UMLDiagrams #TechInterviews #SoftwareEngineering #XMLtoJSON #CleanCode #SoftwareArchitecture #ObjectOrientedDesign #CodingWithExamples #CodeBetter #8WeeksLLDChallenge #JSON