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1. 01

   GuideNewMembers

   API Design for System Design Interviews

   How to design the API in a system design interview and in production: choosing REST, GraphQL or gRPC, modelling resources, status codes, pagination, idempotency keys, ETags, async jobs, versioning, auth and rate limits, with 19 diagrams and a 5-minute interview checklist.

   ~35 min read · Beginner → Senior · 19 diagrams

2. 02

   Guide

   Java Concurrency & Multithreading

   End-to-end, internals-first: JVM memory architecture, CPU cache visibility, all six thread states, synchronized and volatile, wait/notify, thread pools, the full java.util.concurrent toolkit, ThreadLocal, CompletableFuture, the Java Memory Model, common bugs, and a full interview Q&A.

   ~50 min read · Beginner → Advanced · 8 diagrams

3. 03

   Deep diveNew

   Why wait() and notify() Must Be Called Inside synchronized

   The lost-wakeup race that forces the rule, what the monitor’s entry set and wait set really do, why wait() must live in a while loop, notify vs notifyAll, and how Lock/Condition inherits the same contract.

   ~32 min read · Intermediate · 7 diagrams

4. 04

   GuideNew

   Why Strings Are Immutable in Java

   Inside java.lang.String: the final byte[], compact strings and the cached hash, and the five reasons immutability was chosen: the string pool, hash-based collections, security, thread safety and class loading.

   ~30 min read · Beginner → Intermediate · 8 diagrams

5. 05

   Guide

   The Java LLD Rulebook

   A complete, step-by-step guide on how to tackle Low-Level Design and machine coding interview rounds. Learn how to confidently apply Object-Oriented Design principles, leverage common design patterns, and structure scalable Java applications from scratch.

   12-step playbook · Interview prep · 13 diagrams