Explain OOP concepts: inheritance, polymorphism, abstraction, encapsulation. What is the difference between JDK, JRE, and JVM? Explain method overloading vs overriding. What are access modifiers in Java? Difference between ArrayList and LinkedList. What is a static keyword? What are exceptions? Explain try-catch-finally. What is the purpose of a constructor? Explain String, StringBuilder, and StringBuffer. Difference between HashMap and `HashSet