Below is a complete, beginner-to-intermediate guide to Java OOP (Object-Oriented Programming) that covers every single topic

Java OOP (Overview)

Concept	What it means	Why it matters
Class	Blueprint for objects	Reusability
Object	Instance of a class	Real entity
Encapsulation	Data + methods together, hide internals	Security
Inheritance	“is-a” relationship	Code reuse
Polymorphism	Many forms (method overriding / overloading)	Flexibility
Abstraction	Hide complexity, show essentials	Simplicity

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Access Modifiers

Modifier	Class	Package	Subclass	World
Public	✅	✅	✅	✅
protected	✅	✅	✅	❌
private	✅	❌	❌	❌
default	✅	✅	❌	❌