Gunnar Grosch’s Post

this vs super in Java – Simple Explanation 🎯 🔹 this keyword: ▸ Refers to the current class object ▸ this.variable → access current class variable ▸ this() → call current class constructor ▸ Used to resolve naming conflicts class Student { String name; Student(String name) { this.name = name; // refers to current object } } 🔹 super keyword: ▸ Refers to the parent class object ▸ super.variable → access parent class variable ▸ super() → call parent class constructor ▸ Used to access overridden methods class Dog extends Animal { void sound() { super.sound(); // calls Animal's sound() System.out.println("Bark"); } } 🔑 Key Difference: → this = current class → super = parent class 💡 Both can access constructors, variables, and methods — but direction matters: this → inward | super → upward 🔥 Pro Tip: Use this() and super() carefully they must be the first statement in constructor. #Java #CoreJava #OOP #JavaDeveloper #BackendDeveloper #Programming

I was exploring AWS updates this week and found Transform custom A new AI agent that automates codebase modernization at enterprise scale What I Explored: It's an AI agent that learns transformation patterns from your codebase and rolls them out across everything via CLI and web interface Technical Insights Worth Sharing: It handles three modernization layers without you manually touching each file Framework level covers things like Angular to React migrations and Spring Boot dependency chains Runtime level takes care of Python, Java, Node.js version jumps and even understands behavioral differences, not just syntax changes Infrastructure level handles workload migrations from x86 to Graviton and IaC conversions like CDK to Terraform The Stair-Step protocol caught my attention — instead of jumping Angular 16 directly to 19 and hoping for the best, it goes 16 to 17, validates, then 17 to 18, validates, and so on Custom transformations can be defined just by describing what you need in plain language — no complex config upfront

🚀 Spring Boot Learning – @RestController vs @RequestMapping While building REST APIs in Spring Boot, I explored how requests are handled behind the scenes. 🔹 @RestController Used to create REST APIs. It combines @Controller + @ResponseBody and returns data directly (JSON/String). 🔹 @RequestMapping Used to map URLs to classes or methods and can handle different HTTP methods. 💡 Modern Approach (Shortcut Annotations) Instead of using @RequestMapping for everything, Spring provides: -> @GetMapping -> @PostMapping -> @PutMapping -> @DeleteMapping These make code cleaner and more readable. 📌 Key Insight: 👉 @RestController creates APIs 👉 Mapping annotations connect URLs to methods Sharing a simple graphical representation to make this concept easier to understand. 📊 #SpringBoot #Java #BackendDevelopment #RESTAPI #DependencyInjection #JavaDeveloper #LearningInPublic

🧱 SOLID Principles in Java – Write Code That Doesn't Come Back to Haunt You You know that feeling when touching one feature breaks three unrelated things? That's what life looks like without SOLID principles. I just published a deep-dive post covering all five principles with real Java examples: ✅ Single Responsibility – One class, one job. Stop your Invoice class from moonlighting as a printer AND a database. ✅ Open/Closed – Extend behavior without cracking open existing code. No more endless if-else chains. ✅ Liskov Substitution – Your Penguin shouldn't throw UnsupportedOperationException when asked to fly. ✅ Interface Segregation – Stop forcing Robots to implement an eat() method. ✅ Dependency Inversion – Depend on abstractions, not implementations. Your service shouldn't care if it's MySQL or PostgreSQL. 🔗 Read the full post: https://lnkd.in/gfA5g8VG #Java #SOLID #CleanCode #SoftwareEngineering #OOP #DesignPrinciples #BackendDevelopment #SpringBoot #Programming #TechBlog #100DaysOfCode

🚀 Day 53 – Mastering ArrayDeque in Java Today I explored one of the most efficient data structures in Java Collections – ArrayDeque 🔥 📌 Key Learnings: 🔹 ArrayDeque is a resizable array-based Deque (Double Ended Queue) 🔹 Supports insertion & deletion from both ends (front & rear) 🔹 No indexing → cannot use get/set methods 🔹 No null values allowed (throws runtime exception) 🔹 Duplicates & heterogeneous data allowed 🔹 Faster than LinkedList due to no memory overhead ⚙️ Traversal Techniques: ✔ For-each loop ✔ Iterator ✔ Descending Iterator (reverse traversal) 💡 Why ArrayDeque? 👉 O(1) performance for add/remove operations 👉 Best choice for implementing: Stack (LIFO) Queue (FIFO) Deque 🧠 Big Takeaway: ArrayDeque = Fast + Memory Efficient + Flexible (Stack/Queue/Deque in one) Consistency is the key 🔑 — learning something new every day! #Java #DataStructures #ArrayDeque #JavaCollections #CodingJourney #100DaysOfCode #LearningDaily

🚀 Excited to share my latest project — 4mulaQuery! I built a fully functional database engine from scratch — no existing DB libraries used. 🔧 What's under the hood: • Custom C++ storage engine with binary file I/O • Java Spring Boot REST API as the bridge layer • Docker containerized & deployed on Render • Live analytics dashboard with real-time charts • Persistent backend authentication system • ML query logging pipeline (Python + Pandas) 💡 Why I built this: Most developers use databases without understanding how they actually work. I wanted to go deeper — implement binary storage, page management, CRUD from scratch, and expose it all through a clean REST API. 🌐 Live Demo: fourmulaquery.onrender.com 💻 GitHub: https://lnkd.in/gKrjbYGh #OpenSource #Java #CPlusPlus #Docker #SpringBoot #DatabaseEngineering #BuildInPublic

After years of working with Java, microservices, and enterprise systems, I’ve realized: 👉 If you don’t share what you learn, it fades. So I’m starting something new— Learning in public. Sharing real-world concepts. No fluff. No theory dumps. 💡 Topic #1: Why ConcurrentHashMap Beats HashMap in Multithreading If you’ve worked on production systems, you’ve likely seen this: ❌ Using HashMap in multithreaded code → Seems fine… until it isn’t. Then suddenly: Data becomes inconsistent Apps hang (yes, infinite loops during resizing 😬) Random crashes appear ✅ Enter: ConcurrentHashMap Built for concurrency. Built for scale. 🔹 Why it’s better: ✔️ No full-map locking → Uses finer control (segments earlier, CAS + sync now) ✔️ Real parallelism → Threads don’t block each other unnecessarily ✔️ Safe iteration → No ConcurrentModificationException ✔️ Atomic operations → putIfAbsent(), compute(), merge() = safer updates 🧠 Where this actually matters: Caching layers Session handling High-throughput APIs This is just the start. Next posts will break down real backend concepts— the kind you only learn after things break in production. 💬 Curious: Have you ever run into concurrency bugs with HashMap? #Java #Backend #SystemDesign #Microservices #Programming #LearningInPublic

Day 11 — #100DaysOfJava ☕ No new topic today. Only revision — and honestly, it felt more valuable than learning something new. Java Basics ---------------------- ->JVM runs your code. JDK is the full toolkit to write and run Java. JRE is just for running. ->Variables store data — int, double, String, boolean. ->Scanner reads user input from keyboard. I went back through Day 1–9 and here’s my journey in short: • Basics: JVM, JDK, JRE, variables, Scanner • Strings & Arrays: Immutable strings, StringBuilder, fixed-size arrays • OOP: Overloading, overriding, this, super, constructors • Advanced OOP: Abstract classes, inner/anonymous classes, boxing • Interfaces & Lambda: Functional interfaces, lambda, enum • Exceptions & Threads: try-catch, throw/throws, start vs run • Collections: List, Set, Map, Iterator basics • Modern Java: Optional, record, var, sealed classes • Tools: Maven (pom.xml), AWS EC2 basics Big realization: Concepts that confused me earlier now make sense — revision is powerful. Most people rush ahead. Slowing down helped me more. What’s your revision strategy? -What is your revision strategy? -Drop it in the comments . would love to learn from you! Day 1 ....................... 10 ✅ #100DaysOfJava #Java #JavaDeveloper #LearningInPublic #100DaysOfCode #BackendDevelopment #Revision #CodeEveryDay #JavaBeginners #LearnJava

Day 7 of #100DaysOfCode — Java is getting interesting ☕ Today I explored the Java Collections Framework. Before this, I was using arrays for everything. But arrays have one limitation — fixed size. 👉 What if we need to add more data later? That’s where Collections come in. 🔹 Key Learnings: ArrayList grows dynamically — no size worries Easy operations: add(), remove(), get(), size() More flexible than arrays 🔹 Iterator (Game changer) A clean way to loop through collections: hasNext() → checks next element next() → returns next element remove() → safely removes element 🔹 Concept that clicked today: Iterable → Collection → List → ArrayList This small hierarchy made everything much clearer. ⚡ Array vs ArrayList Array → fixed size ArrayList → dynamic size Array → stores primitives ArrayList → stores objects Still exploring: Set, Map, Queue next 🔥 Consistency is the only plan. Showing up every day 💪 If you’re also learning Java or working with Collections — let’s connect 🤝 #Java #Collections #ArrayList #100DaysOfCode #JavaDeveloper #LearningInPublic

🚀 Java Full Stack Journey – Day 32 Today I explored some core concepts of Java Collections — understanding how different data structures like List, Queue, Set, Stack, and ArrayDeque work and when to use them. This session helped me connect how data is stored, accessed, and manipulated efficiently depending on the use case. ✨ Key takeaways from today: ✔️ List – Ordered collection, allows duplicates (like ArrayList) ✔️ Set – No duplicates, useful for unique data handling ✔️ Queue – Follows FIFO (First In First Out) principle ✔️ Stack – Follows LIFO (Last In First Out) principle ✔️ ArrayDeque – A powerful class that can act as both Queue and Stack ✔️ Learned when to prefer ArrayDeque over Stack for better performance ✔️ Understood real-world use cases of each data structure This made me realize how choosing the right data structure can significantly improve performance and code clarity. Big thanks to CoderArmy, Aditya Tandon, and Rohit Negi for explaining these concepts in such a simple and practical way 🙌 Learning step by step and moving closer to becoming a Java Full Stack Developer 💻🔥 #Day32 #Java #FullStackDevelopment #JavaCollections #DataStructures #ArrayDeque #Stack #Queue #Set #LearningJourney #Coding #DeveloperGrowth