Java Bean Bag

🏗 Structure 1️⃣ Setting the Scene — The Confusion Moment 🤔 "I thought JSON was just a HashMap in a superhero costume!!" Nope! It’s like saying Spring Boot is just Spring MVC with coffee ☕ — there’s way more going on. 2️⃣ 💡 What is a HashMap? Java-only data structure Stores key-value pairs in memory (heap) Keys can be anything — Integer, String, custom objects (if hashCode() & equals() are implemented properly) Not meant for network transfer 📦 Example: Map<Integer, String> studentMap = new HashMap<>(); studentMap.put(101, "Anand"); studentMap.put(102, "Priya"); This stays inside your JVM. If you try to send it over HTTP as-is… good luck explaining it to a Python service. 🐍💥 3️⃣ 📝 What is JSON? Language-independent data format (Java, Python, JS, Go, you name it) Stores only String...

  💬 “I changed the object inside a method. But when I came back… NOTHING happened. Java, are you even listening to me?!” 😡 That was me. Screaming at my screen. So I decided to dig deep: What’s really going on? Let’s go from basics → to bugs → to JVM internals → to truth 💡 🎯 What People Think Java Does: public void change ( int x) { x = 10 ; } “Cool, this is pass-by-value. Just a copy. I get it.” ✅ But then... public void update (User u) { u.setName( "Anand" ); } “Wait, it changed outside! That must be pass-by-reference!” ❓ And then... public void update (User u) { u = new User ( "NewGuy" ); } “Now it DIDN’T change outside?!  Java, are you drunk?” 🍺 🧠 Truth Bomb: Java is Always Pass-by-Value. No Exceptions. Even for objects. But here's the tricky twist: 📌 Java passes a copy of the reference when dealing with objects. So you're not passing the object directly — You're passing a copy of the point...