Jullia 𝜗ৎ⋆. 𐙚˚࿔ @debugnox

3 critical security bugs. Code looks completely normal. Ships to production every day. Can you find all 3? 🤔

Tech lead says: If cache is faster than database, why not store everything in cache? What’s your answer?

As a developer, Please Slap yourself if you are unable to explain even 10 from below terms : Indexing Clustering Denormalization Normalization Read replicas Leader–Follower replication Multi-leader replication Quorum Consensus CAP theorem BASE ACID Eventual consistency Strong consistency Snapshot isolation MVCC (Multi-Version Concurrency Control) Two-phase commit (2PC) Three-phase commit (3PC) Write-ahead logging (WAL) Checkpointing Compaction Rebalancing Resharding Data locality Hot partition Split-brain Failover High availability (HA) Horizontal scaling Vertical scaling Load balancing Connection pooling Caching Materialized views Secondary indexes Composite index Covering index Bloom filter LSM tree B-tree Query planner Cost-based optimizer Deadlock Lock escalation Optimistic locking Pessimistic locking Dirty read Phantom read Read skew Write skew Data skew Backpressure Circuit breaker Throttling Rate limiting CDC (Change Data Capture) Logical replication Physical replication Geo-replication Federation Data lake Data warehouse Columnar storage Row-based storage Time-series partitioning Hash partitioning Range partitioning Consistent hashing Data migration Schema evolution Schema registry Idempotency

Perguntas de entrevista backend que eu gosto - como tornar um request idempotente? - o que fazer quando o webhook que você espera não chega? - quando usar uma state machine? - como garantir que os dados estão consistentes? o que mais?

Coisas que todo Dev deveria saber explicar sem Google - o que é um processo - o que é uma thread - o que é um socket - o que é um índice - o que é uma transação o que mais?

25 Springboot annotations that are good to know before your interview : 1. @ SpringBootApplication: Combines @ Configuration, @ EnableAutoConfiguration, and @ ComponentScan annotations for configuring, enabling auto-configuration, and component scanning in Spring Boot applications 2. @ Component: Marks a class as a Spring-managed bean, making it available for dependency injection 3. @ Service: Specialized form of @ Component used to annotate service-layer classes in the application 4. @ Repository: Marks a data access object (DAO) class, signaling to Spring that it will handle database interactions. It also enables exception translation, so database-related exceptions are caught and translated into Spring’s DataAccessException 5. @ Controller: Used to define a controller in the MVC (Model-View-Controller) framework. This annotation handles HTTP requests by mapping them to specific methods in a controller class. 6. @ RestController: Combines @ Controller and @ ResponseBody, simplifying the development of RESTful APIs by automatically converting response data to JSON or XML. 7. @ RequestMapping: Maps HTTP requests to handler methods. It can be applied at the class or method level and allows for specifying HTTP method types (GET, POST, etc.) and paths 8. @ GetMapping, @ PostMapping, @ PutMapping, @ DeleteMapping: Variants of @ RequestMapping for handling specific HTTP request methods (GET, POST, PUT, DELETE) in REST APIs, making the code more readable and concise. 9. @ Autowired: Used for dependency injection by automatically injecting an instance of a bean into a class. It can be applied to constructors, fields, or setters. 10. @ Qualifier: Works with @ Autowired to resolve ambiguity when multiple beans of the same type are present, allowing you to specify the exact bean to inject. 11. @ Value: Injects values into fields from application properties or environment variables, making it easy to use external configuration values. 12. @ Configuration: Marks a class as a source of bean definitions for the application context, used for Java-based configuration. 13. @ Bean: Indicates that a method produces a bean that should be managed by the Spring container, typically used in combination with @ Configuration. 14. @ ConfigurationProperties: Maps properties from application.properties or application.yml files to a Java class, allowing easy access to configuration properties with complex structures. 15. @ Profile: Specifies which beans should be created based on the active profile, allowing you to set up different configurations for different environments (e.g., dev, test, production). 16. @ EnableAutoConfiguration: Enables automatic configuration in Spring Boot by scanning the classpath and enabling configurations for various Spring modules, like JPA or RabbitMQ. 17. @ EnableAsync: Enables asynchronous method execution, allowing you to run methods in a separate thread without blocking the main thread. 18. @ Scheduled: Used to schedule tasks in Spring, enabling the execution of methods at specific intervals. 19. @ Transactional: Ensures that methods execute within a transaction, rolling back on exceptions and committing changes upon successful execution. It’s often used for database operations. 20. @ CrossOrigin: Configures cross-origin resource sharing (CORS) to control how resources are shared with frontend clients from different domains, helping manage security in REST APIs. 21.@ Primary: Used alongside @ Autowired to resolve dependency conflicts by setting a default bean when multiple implementations exist. 22. @ Lazy: Delays bean initialization until needed, optimizing memory and startup time, especially for costly or rarely used beans. 23.@ Conditional: Allows custom conditions for bean creation, enabling complex conditional logic. 24.@ ConditionalOnBean: Creates a bean only if another specific bean is already present in the context, useful for configuring dependencies dynamically. 25.@ Cacheable

90% of Java in 2026 comes down to mastering these 10 concepts: 1) JVM memory model + GC basics Know heap vs off-heap, allocation rates, and how G1/ZGC choices change tail latency. 2) Concurrency primitives Threads are easy; correctness is hard. Understand executors, CompletableFuture, virtual threads, and where blocking still bites. 3) Collections + complexity HashMap, ConcurrentHashMap, queues, and caches. Know the big-O and the constant factors that show up at 50k rps. 4) IO and backpressure HTTP clients, JDBC, Kafka, and file IO. If you ignore backpressure, you build self-DDoS under load. 5) Spring (or framework) internals DI, proxies, transaction boundaries, and lifecycle hooks. Most prod bugs are mis-scoped beans and surprising AOP. 6) Data access tradeoffs Indexes, isolation levels, N+1 queries, batching, and idempotency keys. The database is still the main bottleneck. 7) Tooling that speeds diagnosis jcmd/jstack, JFR, async-profiler, heap dumps. Learn to answer: CPU bound, lock bound, or GC bound in 10 minutes. 8) Logging and metrics discipline Structured logs, correlation IDs, RED/USE metrics, and sane cardinality. High-card labels can take down your monitoring bill. 9) Security defaults TLS, secrets handling, dependency scanning, deserialization risks, and input validation. Most incidents start as boring misconfig. 10) Real-world failure modes Retries without jitter, unbounded queues, timeouts missing, and circuit breakers mis-tuned. These show up on-call, not in unit tests. [generated using my AI agent, hope this was useful]

Git commands developers actually use: `git status` → What's happening? `git add .` → Stage changes `git commit -m ""` → Save changes `git pull` → Get updates `git push` → Send changes `git branch` → View branches `git switch` → Change branch `git diff` → See changes `git log` → View history `git stash` → Hide changes temporarily Which Git command do you always forget?

Think Java only leads to boring enterprise jobs? Here’s what you can actually build your career around: Java + Spring Boot → Backend Engineer Java + Kafka → Distributed Systems Engineer Java + Spring Cloud → Microservices Engineer Java + Hibernate → Enterprise Backend Developer Java + Docker → Cloud Engineer Java + Kubernetes → Cloud Native Engineer Java + AWS → Cloud Backend Engineer Java + Redis → High-Performance Backend Engineer Java + Elasticsearch → Search Engineer Java + Android → Android Developer One language. More career paths than most people realize. bookmark this if you’re planning to learn Java 🔖

As a dev do you know the difference between - idempotency - deduplication Most devs get confused.

40 OOP questions you can prepare for your interviews 1. What is Object-Oriented Programming? 2. What are the four pillars of OOP? 3. What is the difference between a class and an object? 4. What is encapsulation? Why is it useful? 5. What is abstraction? Why do we need it? 6. What is inheritance? What are its advantages and disadvantages? 7. What is polymorphism? What are its types? 8. What is the difference between abstraction and encapsulation? 9. What is the difference between inheritance and composition? 10. What is the difference between association, aggregation, and composition? 11. What is a constructor? Why do we need it? 12. What is constructor overloading? 13. Can a constructor be inherited or overridden? 14. What is the difference between method overloading and method overriding? 15. What is compile-time polymorphism vs runtime polymorphism? 16. How does runtime polymorphism/dynamic method dispatch work? 17. What is the purpose of the this keyword? 18. What is the purpose of the super keyword? 19. What are static variables and static methods? 20. Can a static method be overridden? 21. What are the different types of inheritance? 22. What is multiple inheritance and why doesn't Java support it through classes? 23. What is the diamond problem? 24. What is an abstract class? 25. What is an interface? 26. What is the difference between an abstract class and an interface? 27. Can an abstract class have constructors and concrete methods? 28. Can we create an object of an abstract class? 29. What happens when a child class doesn't implement all abstract methods? 30. When would you choose an interface over an abstract class? 31. What is upcasting and downcasting? 32. What is object cloning? What is shallow copy vs deep copy? 33. What is an immutable class? How would you design one? 34. What is object equality? What is the difference between reference equality and logical equality? 35. What is coupling? What is the difference between tight and loose coupling? 36. What is cohesion, and why is high cohesion preferred? 37. What are the SOLID principles? Explain each with an example. 38. Why is composition often preferred over inheritance? 39. What are common design patterns such as Singleton, Factory, Strategy, Observer, and Builder, and when would you use them? 40. Design an OOP system such as a Parking Lot, Library Management System, Elevator, ATM, or Notification System. How would you identify the classes, interfaces, relationships, and responsibilities?

Most Java developers have 50+ GitHub repos bookmarked. But how many of them actually made you a better developer? Here are 10 GitHub repositories I’d actually recommend studying if you want to get better at Java 👇 🧵

90% of Java in 2026 comes down to mastering these 10 concepts: 1) Memory model + GC basics: know what creates allocation pressure, how to read a heap dump, and why GC tuning is usually a symptom, not the fix. 2) Concurrency primitives: threads vs executors, locks vs atomics, and why blocking on the wrong pool turns a small slowdown into a full outage. 3) Modern Java language features: records, sealed types, pattern matching, and using them to reduce null checks and boilerplate without hiding control flow. 4) HTTP client behavior: timeouts (connect/read), connection pools, retries with budgets, and idempotency keys so failures don’t duplicate writes. 5) DB transaction boundaries: isolation levels, deadlocks, and the trap of doing external calls inside a transaction while holding locks. 6) Dependency management: Maven/Gradle version conflicts, shading, and SBOMs; most prod weirdness starts as a transitive jar you didn’t know you pulled. 7) Debugging in prod: jstack, async-profiler, heap histograms, and capturing one good thread dump during the incident beats 3 hours of log scrolling. 8) Observability that answers questions: structured logs with request IDs, metrics with percentiles, and traces across queues so you can see where latency lives. 9) Security fundamentals: deserialization and templating risks, secret handling, TLS validation, and supply chain scanning that actually blocks known bad CVEs. 10) Real-world mistake patterns: leaking ThreadLocals, forgetting to close streams, using default charset/timezone, and treating backpressure as optional until p99 goes vertical

To become a world-class software engineer, you should read these 20 books:

Java multithreading interview questions for beginners - - difference between synchronized blocks and the volatile keyword. - Explain the concept of reentrant locks in Java - difference between Thread.sleep() and Object.wait() methods - What is a thread-local variable in Java?

Every software developer needs to know how the HTTP protocol works. Here are the 8 fundamental things you need to grasp:

Don't put Hibernate or JPA in your CV if you can't explain N+1 query problem...

Please Don’t overcomplicate it. • Build a Password Manager to learn file handling, hashing (not full crypto) • Build a URL Shortener to understand routing, IDs, and persistence • Build a Todo App with deadlines to practice CRUD and basic state • Build a Web Scraper to learn requests, parsing, and rate limits • Build a CLI Expense Tracker to master logic, files, and edge cases • Build a Log Analyzer to work with files, timestamps, and patterns • Build a Simple Recommender using similarity rules (not ML magic) • Build an Email Automation Script using SMTP and scheduling PROJECTS. Not tutorials.

You’re a FOOL if you’re learning networking and still don’t know these 19 things: 1. IP Address    Tells networks where a device/interface can be reached. 2. MAC Address    Used to identify network interfaces inside a local Layer 2 network. 3. Subnet Mask    Tells you which part of an IP represents the network and which part represents the host. 4. Default Gateway    The router your device sends traffic to when the destination is outside its local network. 5. DNS    Turns names like `google.com` into IP addresses. 6. DHCP    Automatically gives devices their IP, gateway, DNS, and other network settings. 7. Switch    Connects devices inside a LAN and forwards Ethernet frames using MAC addresses. 8. Router    Connects different networks and forwards packets using IP addresses. 9. ARP    Maps an IPv4 address to a MAC address on the local network. 10. TCP     Connection-oriented and designed for reliable, ordered delivery. 11. UDP     Connectionless with lower overhead, useful when speed and low latency matter more than guaranteed delivery. 12. Ports     Tell the operating system which application should receive traffic. Common ones: `22` → SSH `53` → DNS `80` → HTTP `443` → HTTPS 13. Private IPs     Used inside private networks. Main IPv4 ranges: `10.0.0.0/8` `172.16.0.0/12` `192.168.0.0/16` 14. NAT     Translates addresses between networks, commonly allowing private devices to reach the internet through public IPs. 15. Public subnet ≠ public resource     Being inside a public subnet alone does NOT automatically make a cloud resource publicly reachable. 16. Firewall     Controls which traffic is allowed or denied based on rules such as IP, protocol, and port. 17. ICMP     Used for network diagnostics and control messages. `ping` commonly uses ICMP. 18. CIDR     Defines network ranges. `/16` → larger network `/24` → smaller network `/32` → one IPv4 address 19. The most important networking skill: follow the packet. When something breaks, check: Device ↓ DNS ↓ IP + Subnet ↓ Gateway ↓ Route ↓ Firewall ↓ Destination Stop memorizing networking as 100 disconnected definitions. Understand how a packet gets from A → B, and most networking concepts start making sense. Bookmark this before your next networking session.

Java devs, how many of these skills are on your CV? 1. Distributed Caching : Redis, Memcache 2. Monitoring : Splunk, Dynatrace, Grafana, ELK 3. Messaging : Kafka, JMS, RabbitMQ 4. Testing : TDD, Mockito, JUnit 5. CI/CD & Containers : Jenkins, GitHub Actions, Docker, Kubernetes 6. Frameworks : Spring Boot, Spring MVC, Apache Camel 7. Microservices : Config Server, API Gateway, Service Discovery, Resilience4j 8. Multithreading & Concurrency : Executors, ForkJoin, CompletableFuture 9. Security : Spring Security, OAuth2, JWT 10. Persistence : Hibernate, JPA, MyBatis 11. API Development : REST, Swagger, OpenAPI 12. Reactive Programming : WebFlux, RxJava, Reactor 13. Build Tools : Maven, Gradle 14. Code Quality : SonarQube, PMD, Checkstyle 15. Cloud : AWS, GCP, Azure 16. Java Versions : Java 8:21 features 17. Design Principles : SOLID, Design Patterns, Clean Architecture