The problem A customer places an order worth INR 5,000. The Payment Service captures the money. Then the Inventory Service tries to reserve the product and fails, because the stock is gone. Now the sy
Examples come from CircuitCraft, an e-commerce project I use to make every concept concrete. Imagine a customer places an order on CircuitCraft. The system must save the order, generate an invoice, se
A production-style design that combines REST API design, idempotency, versioning, pagination, API gateways, rate limiting, Redis, retries, RabbitMQ and webhooks. After two days of studying API desig
System Design Series, Part 2. In Part 1 we covered API design: REST, idempotency, versioning, pagination and status codes. This part covers what sits in front of your services and how they survive fai
Introduction Good API design comes down to one idea: your system should behave predictably even when the network does not. Requests get lost, clients retry, and old apps keep calling endpoints you hav
An interface in Java is a blueprint of a class that defines a set of abstract methods, constants, and (since Java 8) default and static methods. It serves as a contract, specifying behaviors that implementing classes must provide. Interfaces are decl...
Object-oriented programming (OOP) is a powerful programming paradigm that organizes code around objects—entities that combine data (attributes) and behavior (methods). At the heart of OOP in Java are three fundamental concepts: inheritance, polymorph...