Polymorphism aur Interfaces

Ek interface un methods ka set define karta hai jo ek class ko implement karna chahiye, jo implements se declare hota hai. extends ke bar-aks, ek class ek sath multiple interfaces implement kar sakta hai, aur bilkul alag classes — Circle aur Square yahan Shape ke alawa kuch share nahi karte — sab same interface ko satisfy kar sakte hain.

public class Main {
    interface Shape {
        double area();
    }

    static class Circle implements Shape {
        double radius;

        Circle(double radius) {
            this.radius = radius;
        }

        public double area() {
            return 3.14159 * radius * radius;
        }
    }

    static class Square implements Shape {
        double side;

        Square(double side) {
            this.side = side;
        }

        public double area() {
            return side * side;
        }
    }

    public static void main(String[] args) {
        Shape[] shapes = { new Circle(2), new Square(3) };
        for (Shape s : shapes) {
            System.out.println(s.area());
        }
    }
}

12.56636
9.0

shapes, Shape ka ek array hai — interface type — lekin har element phir bhi sahi class ka khud ka area() implementation call karta hai. Yeh dynamic dispatch hai: kaunsa actual method chalta hai yeh runtime par object ki real class ke basis par decide hota hai, variable ke declared type ke basis par nahi.

Aage: abstract classes — ek regular class aur interface ke darmiyan ka hybrid, ek contract aur real implementation code dono share karne ke liye.