DevNotes
Master modern backend technologies
Free, deep and interview-focused backend notes for Java developers: Core Java, Collections, Java 8, multithreading, design patterns, Spring Boot and SQL — with runnable code, diagrams and interview Q&A.
Java
Core Java fundamentals through modern Java features.
- Core Java — 13 chapters
- Collection Framework — 23 chapters
- Java 8 & Streams — 22 chapters
- Exception Handling — 12 chapters
- Reflection — 10 chapters
- Multithreading — 19 chapters
Spring
Spring Core, Spring Boot, Data JPA and Security.
- Spring Boot — 28 chapters
- Spring Data JPA & Hibernate — 17 chapters
- Spring Security & JWT — 6 chapters
- Logging (SLF4J & Log4j2) — 3 chapters
Design Patterns
Creational, structural, behavioral and microservices patterns with runnable Java code — and where Spring uses them.
- Essential Design Patterns — 12 chapters
Microservices
Messaging and event-driven architecture: Apache Kafka, service communication and resilience.
- Apache Kafka Masterclass — 15 chapters
- Microservices Fundamentals — 12 chapters
Database
SQL, indexing, transactions and JPA.
- SQL & MySQL — 31 chapters
System Design
Scalability, caching, queues and real-world architectures.
- System Design Basics — 14 chapters
Real-World Scenarios
Production troubleshooting and scenario-based interview questions with full answers.
- Java Backend Production Scenarios — 8 chapters