OOP Concepts: Encapsulation, Inheritance, Polymorphism, Abstraction.
JVM, JRE, JDK: Understanding their roles and differences.
Data Types and Variables: Primitive types, reference types, scope, and default values.
Control Structures: if-else, switch, loops (for, while, do-while).
Arrays and Collections: ArrayList, LinkedList, HashMap, HashSet, TreeSet, their differences, and use cases.
String Handling: String, StringBuffer, StringBuilder, and their immutability.
Exception Handling: try-catch-finally, custom exceptions, checked vs. unchecked exceptions.
