Jullia 𝜗ৎ⋆. 𐙚˚࿔ @debugnox

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

As a Java Developer, Please slap yourself if you cannot clearly explain at least 10 of the following: Java Memory Model (JMM) Happens-before relationship Volatile visibility guarantees Instruction reordering Escape analysis False sharing CAS (Compare-And-Swap) ABA problem AQS internals ForkJoinPool Virtual threads Semaphores GC roots G1 GC Object header layout Generics type erasure Bridge methods Double-checked locking readResolve SerialVersionUID StampedLock optimistic reads NIO Selector internals DirectByteBuffer lifecycle ClassLoader delegation model JIT inlining heuristics @ Transactional proxy MethodHandles VarHandle Sealed Classes Predicate Lock inflation Write barriers DispatcherServlet Stream short-circuiting Spliterator try-with-resources

If you're a backend engineer, Please learn: > SOLID design principles > Multithreading > Immutability > Streaming & messaging > Caching > Idempotency > Security > SSL, JWT, OAuth > Design patterns (Factory, Decorator, Singleton, Observer/Observable) > TDD (Test-Driven Development)

How do generics improve type safety in Java? Why does type erasure exist, and what problems does it create? How would you explain bounded wildcards in a practical codebase? What happens when you mix generics with reflection or legacy raw types?

Don't even think about going for a Java Microservices Interview if you are not clear about these 5 concepts: 1. Event-Driven Architecture - Services talk via events. 2. Observability - Logs + metrics + traces 3. Circuit Breaker - Fail fast, protect your system. 4. Sharding - Split large datasets across nodes. 5. Rate Limiting (Token Bucket) - Protect APIs under load.

90% of Java in 2026 comes down to mastering these 10 concepts. Everything else is syntax trivia. 1) JVM memory model + GC: know heaps, generations, and how allocation rate drives pauses more than heap size. 2) Concurrency primitives: locks vs atomics vs executors; most prod bugs are missed visibility, not deadlocks. 3) Collections + complexity: HashMap resizing, iteration costs, and when LinkedList is just a slow ArrayList. 4) I/O and backpressure: blocking vs NIO, thread-per-request limits, and how queues hide overload until they don’t. 5) Exceptions and failure semantics: checked exceptions are not reliability; timeouts, retries, and idempotency are. 6) Performance basics: JIT warmup, profiling before tuning, and why microbenchmarks lie without JMH. 7) Tooling fluency: Maven/Gradle, dependency trees, shading, and reproducible builds across CI and laptops. 8) Debugging in prod: thread dumps, heap dumps, async-profiler, and reading stack traces without guessing. 9) Security hygiene: deserialization, SSRF, secrets in logs, and keeping dependencies patched with SBOM/SCA. 10) Observability that helps: structured logs, metrics with cardinality limits, tracing with sampling, and SLO-driven alerts

99% of Java developers have written this bug at least once. It works... Until it doesn't. Using == for String comparison may appear correct during testing because of String interning, but it can fail when values come from a database, REST API, or user input. The safest habit is simple - Use .equals() to compare values. - Put the constant first: "SUCCESS".equals(status) It avoids a NullPointerException even if status is null. Small habits like this prevent real production bugs. What's another Java gotcha that every developer should know?

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