Explain abstraction and encapsulation with example. How does polymorphism work in object oriented programming? Write.

OOP models real-world entities as objects with data + behaviour.

Abstraction — show what, hide how: Expose only essential features. Example: car.start() button — driver need not know fuel-injection code. In Java: abstract class Shape { abstract float area(); } — user calls area() without knowing circle vs rectangle formula.

Encapsulation — bundle + protect: Wrap data and methods in one class and hide internals with private + public getters/setters.

class Citizen {
  private String citizenshipNo; // hidden
  public String getNo() { return citizenshipNo; }
  public void setNo(String n) { if(n.length()==10) citizenshipNo=n; }
}

Direct obj.citizenshipNo="x" is blocked; validation inside setter prevents wrong IDs — data integrity.

Polymorphism — same name, different forms:

1. Compile-time (overloading): Same method name, different parameters. add(a,b) vs add(a,b,c) — compiler picks by signature.
2. Runtime (overriding): Child redefines parent method. Animal.sound() → Dog.sound() barks, Cat.sound() meows. At runtime Animal a = new Dog(); a.sound(); plays bark.

Benefit: one interface (payTax()), many implementations (salary vs business) — extensible code for e-governance modules.