🟢 CORE JAVA (OOP, Collections, Exception, Multithreading) 1️⃣ Explain OOP principles in Java. Encapsulation Abstraction Inheritance Polymorphism 👉 Give real-time example from your Spring Boot project (like User → Admin inheritance). 2️⃣ Difference between List, Set, and Map? Explain: ArrayList vs LinkedList HashSet vs TreeSet HashMap vs ConcurrentHashMap 3️⃣ What is the difference between HashMap and ConcurrentHashMap? 4️⃣ How does HashMap internally work? 5️⃣ What is the difference between checked and unchecked exceptions? 6️⃣ What is the difference between throw and throws? 7️⃣ What is Multithreading in Java? 8️⃣ Difference between Runnable and Thread class? 9️⃣ What is Synchronization? Why is it needed? 🔟 What is the difference between String, StringBuilder, and StringBuffer? 🟢 SPRING BOOT & SPRING MVC 1️⃣1️⃣ What is Spring Boot? Why is it preferred over Spring? 1️⃣2️⃣ What are the advantages of Spring Boot?