What are the four pillars of Object-Oriented Programming in Java?

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The four pillars of OOP in Java are encapsulation, inheritance, polymorphism, and abstraction. Encapsulation — bundle data and methods inside a class; expose only via getters/setters with private fields. Inheritance — a child class reuses behavior from a parent via extends ; promotes code reuse. Polymorphism — one interface, many forms. Overloading (compile-time) and overriding (runtime) let the same method name behave differently. Abstraction — hide implementation details; expose only the contract via abstract classes and interfaces . Give a concrete example for each pillar, not just definitions. The Shape/Circle/Rectangle hierarchy demonstrates three pillars at once. Mention that Java supports single class inheritance but multiple interface inheritance.