Rajat's Notes
Q&A mode on. Open any topic to see interview questions only.
Reference
Glossary
Cross-cutting terms buried inside bigger topics: CQRS, Saga, MVCC, Fencing Token, WAL, and more, each linking straight to the exact section
Java Core
OOP in Java
Pillars, SOLID, composition, records, sealed classes
Collections
HashMap internals, HashSet, TreeMap, ConcurrentHashMap, fail-fast iterators
Memory Model (JMM)
Happens-before, volatile, synchronized, atomics, safe publication
Threads & Concurrency
ThreadPoolExecutor, CompletableFuture, locks, ForkJoin
Virtual Threads
Project Loom, structured concurrency, scoped values
JVM Internals
Memory areas, G1GC, ZGC, JIT, OOM types, class loading
JVM Playground
Interactive simulator for memory, GC, and JIT behavior
Design Patterns
Factory, Builder, Proxy, Decorator, Strategy, Observer, CQRS
Generics
Type bounds, wildcards, PECS, type erasure, heap pollution
Streams & Functional Java
Stream pipeline, collectors, flatMap, Optional, method references
Bitwise & Hacks
AND/OR/XOR/shifts, odd check, power-of-2, bit flags, XOR tricks, HashMap internals
Version History
What shipped in each version, LTS spoken answers, the 8 → 21 migration story
Spring
Spring Lifecycle
Bean lifecycle, ApplicationContext, scopes, auto-configuration
JPA & Hibernate
Persistence context, N+1, fetch strategies, projections, second-level cache
Transactions
Propagation, isolation, SAGA, outbox pattern, distributed transactions
Spring Security
Filter chain, OAuth2/JWT, method security, CORS, CSRF, async context
Threads & Async in Spring
@Async, WebFlux, virtual threads, TaskExecutor, reactive pipelines
Spring Testing
@WebMvcTest, @DataJpaTest, Testcontainers, MockBean, @Async testing, security testing
Distributed Systems
Kafka & Events
Topics, consumer groups, delivery semantics, outbox pattern, error handling
Resiliency
Circuit Breaker, Retry, Bulkhead, Rate Limiter, Service Mesh
Redis
Data structures, caching strategies, pub/sub, Lua scripts, cluster mode
Production Debugging
Incident scenarios: duplicate orders, latency spikes, memory leaks, Kafka consumers, K8s restarts
Consensus & Leader Election
Raft, Paxos, ZAB, quorum math, split-brain, Kafka KRaft/etcd/ZooKeeper as instances
Distributed ID Generation
Snowflake bit layout, UUIDv7, clock skew, worker ID coordination
System Design
Capacity Numbers
RPS, memory sizing, thread pools, latency reference
HTTP Methods & REST
GET/POST/PUT/PATCH/DELETE semantics, idempotency, status codes by operation, idempotency keys
gRPC, REST & GraphQL
Proto files, 4 streaming modes, Spring for GraphQL, N+1 fix, comparison table, when to use each
Docker & Kubernetes
Multi-stage Dockerfile, JVM container flags, health probes, requests vs limits, HPA, zero-downtime tricks
Observability
Structured logging, MDC, Micrometer metric types, JVM & HikariCP metrics, distributed tracing, JVM flags, Prometheus alerts
System Design Tradeoffs
Queue vs topic, sync vs async, WebSocket vs SSE, monolith vs microservices, Redis structure picker, and links to SQL vs NoSQL / Kafka vs RabbitMQ / sharding
AI Engineering
AI Engineering Hub
AI vs ML vs MLOps Engineer, 2026 screening checklist, Java/Spring AI vs Python, RAG project gap analysis
Evals & LLM Testing
Offline eval sets, online evaluation, RelevancyEvaluator/FactCheckingEvaluator, task success/latency/cost
Agents & MCP
Tool calling, ReAct loop, structured outputs, MCP client/server, LangGraph4j vs Spring AI
RAG Deep Dive
Chunking strategy, SearchRequest tuning, hybrid retrieval + RRF, reranking, pgvector vs dedicated vector DBs
LLM Observability
gen_ai Micrometer metrics, tracing a RAG call, OTel GenAI conventions, cost-per-task, Prometheus/Grafana/Datadog
Frontend & Fullstack
Frontend & Fullstack Hub
React vs Angular side by side, Spring/Java-to-frontend concept map, 2026 fullstack screening checklist
React
Hooks mental model, reconciliation & keys, React 18 concurrent features, server state vs client state
Angular
Standalone vs NgModules, change detection & OnPush, hierarchical DI, RxJS switchMap/mergeMap/concatMap/exhaustMap
Frontend Security
XSS, CSRF & SameSite, CORS from the calling side, JWT storage tradeoffs, OAuth2 Authorization Code + PKCE
API Integration Patterns
Auth interceptors, error normalization, TanStack Query caching, secrets-in-bundle gotcha, WebSocket handshake auth
Fullstack System Design
CSR/SSR/SSG/ISR tradeoffs, Core Web Vitals levers, state architecture at scale, micro-frontends, a11y
Dev Tooling
Git CLI
Daily workflow, branching, rebasing, undoing changes, bisect, reflog
Anti-Patterns
Null Object, Boolean Trap, Anemic Model, Service Locator, @Transactional pitfalls
NeetCode 150
NeetCode 150 Tricks
Per-problem trick log: patterns to reach for, sorted by problem number
Data Structures & Algorithms
DSA Hub & Cheatsheet
Recognition cheatsheet, Tricks Vault, complexity reference, catalog index
Java API Cheatsheet
Character, Integer, String, Math, Arrays, Collections, Map (getOrDefault, computeIfAbsent, merge)
Recursion vs Backtracking vs DP
The 30-second decision, trigger words, and the same-domain-different-question contrast that flips the technique
Trees & Binary Trees
Traversals, vertical order (column-index trick), LCA, diameter, BST properties
Binary Search
Lower/upper bound, rotated array, search-on-answer, boundary & overflow gotchas
Two Pointers
Converging & same-direction patterns, 3Sum, Dutch National Flag, trapping rainwater
Hashing
Complement lookup, frequency count, grouping, prefix sum + hash, longest consecutive
Sliding Window
Fixed & variable windows, min window substring, have/need counters, monotonic deque max
Linked Lists
Reversal, fast/slow pointers, Floyd's cycle detection, merge, reorder, copy with random
Stacks, Queues & Monotonic Stack
ArrayDeque, Min Stack, next greater element, histogram, sliding window max
Heaps & Priority Queues
Kth largest, top-K, merge K lists, median of stream, two-heap pattern
Graphs
BFS, DFS, cycle detection, topological sort, Dijkstra, multi-source BFS
Backtracking
Subsets, permutations, combination sum, N-Queens, Word Search, pruning strategies
Dynamic Programming (1D)
Fibonacci-style, House Robber, Coin Change, LIS, Decode Ways, patience sort
Dynamic Programming (2D)
Grid paths, LCS, edit distance, 0/1 knapsack, unbounded knapsack, interleaving string
Prefix Sum & Difference Array
Range queries, subarray sum = k, product except self, 2D prefix sum, range updates
Greedy & Intervals
Merge intervals, meeting rooms, non-overlapping, jump game, task scheduler, gas station
Union-Find
Path compression, union by rank, component count, accounts merge, cycle detection
Topological Sort
Kahn's BFS, DFS postorder, alien dictionary, parallel courses, cycle detection
Arrays & Strings
Kadane's, Dutch National Flag, Boyer-Moore, triple reverse, next permutation, expand palindrome
BFS
Level-order, shortest path, multi-source, 0-1 BFS, bidirectional BFS
DFS
Graph/grid/tree DFS, return-value pattern, 3-color cycle detection, state-space DFS
Tries
Insert/search/prefix, wildcard, Word Search II, binary trie for max XOR
Fast & Slow Pointers
Floyd's cycle detection, cycle entry, find middle, find duplicate, happy number
Monotonic Stack & Deque
Next greater element, histogram, sliding window max, remove k digits
Segment Tree & Fenwick Tree
Range sum/min/max with updates, BIT inversion count, lazy propagation
Advanced Data Structures
LRU Cache, LFU Cache, RandomizedSet, TreeMap patterns, design problems
DP — Interval & String
Burst Balloons, palindrome subsequence, merge stones, regex matching, wildcard
Cyclic Sort
Missing number, find all missing, find duplicate, first missing positive
Sweep Line
Max overlap, skyline problem, My Calendar, event-based processing
LLD
LLD Hub
HLD vs LLD, repeatable approach, recurring patterns cheat sheet, catalog index
Method Walkthrough
The 8-step approach run against a real prompt (vending machine), step by step, before you try one cold
Delivery Protocol
Narration rulebook: sub-problems first, one "because" per decision, error recovery, speakable lines
Parking Lot
Vehicle/spot fit rules, Strategy pricing, extensibility stress-test
Elevator System
State pattern lifecycle, dispatch Strategy, Observer for arrivals
Rate Limiter
Token bucket vs sliding window, Factory, distributed Redis stress-test
Databases
Database Hub
SQL vs NoSQL decision tree, ACID vs BASE, isolation levels cheat, CAP theorem, full catalog
SQL Fundamentals
JOINs, aggregations, CTEs, window functions, NULL handling, keyset pagination, Spring JPA patterns
Indexes
B-tree internals, composite index ordering, covering indexes, partial indexes, GIN/BRIN, index bloat
Database Internals
Pages, buffer pool, WAL, checkpoints, MVCC tuple headers, TOAST, autovacuum, dead tuple bloat
Query Planning & EXPLAIN
EXPLAIN ANALYZE, scan types, join algorithms, buffer hits, pg_stat_statements, slow query log
ACID & Transactions
ACID properties, isolation levels, MVCC, SELECT FOR UPDATE, deadlocks, 2PC, savepoints
Schema Design
Normal forms, FK behaviors, UUID vs BIGSERIAL, soft delete, audit log, jsonb, EAV anti-pattern
SQL vs NoSQL
CAP theorem, ACID vs BASE, decision framework, common mistakes, polyglot persistence
Document DBs (MongoDB)
Embed vs reference, CRUD, indexes, aggregation pipeline, transactions, Spring Data MongoDB
Wide-Column (Cassandra)
Partition key, clustering key, query-driven design, consistency levels, CQL, anti-patterns
Replication & HA
Streaming replication, sync vs async, read replicas, PgBouncer, HikariCP, Patroni failover
Distributed & Sharding
Range/hash sharding, 2PC, Saga pattern, CockroachDB, when you actually need this
Performance Patterns
N+1, partitioning, materialized views, pool sizing, bulk inserts, caching strategies, vacuum