1. What is the difference between JDK, JRE, and JVM? JDK: Java Development Kit – tools to develop Java apps (includes JRE + compilers). JRE: Java Runtime Environment – runs Java applications (includes JVM + libraries). JVM: Java Virtual Machine – executes Java bytecode. --- 2. What are the main OOP principles in Java? Encapsulation: Wrapping data using classes. Inheritance: Acquiring properties from a parent class. Polymorphism: Same method, different behavior. Abstraction: Hiding internal details and showing functionality. --- 3. What is the difference between == and .equals()? == checks reference (memory address). .equals() checks content/value. --- 4. What is a constructor? A constructor is a special method used to initialize objects. It has the same name as the class and no return type. --- 5. What is method overloading and overriding? Overloading: Same method name, different parameters (within the same class). Overriding: Subclass redefines a