Polymorphism

Polymorphism means many forms: different objects can answer the same command in their own ways. Tell every animal to speak, and the dog barks while the cat meows.

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Polymorphism

Syntax

csharp

BaseType variable = new DerivedType();
variable.MethodName();   // runs the DerivedType override

List<BaseType> items = new List<BaseType> { new DerivedA(), new DerivedB() };

Polymorphism

Polymorphism lets you treat objects of different derived types uniformly through a shared base type or interface, while each still runs its own overridden behavior.

A single List<Shape> can hold circles, squares, and triangles, and calling Area() on each invokes the right implementation automatically. This is what makes overriding genuinely useful rather than just syntax.

Note: Polymorphism is why you can write one loop that works correctly no matter which subclass each object actually is.

Example: Polymorphism

markup

using System;
using System.Collections.Generic;

class Shape
{
    public virtual double Area() => 0;
}

class Circle : Shape
{
    public double Radius;
    public Circle(double r) { Radius = r; }
    public override double Area() => Math.PI * Radius * Radius;
}

class Square : Shape
{
    public double Side;
    public Square(double s) { Side = s; }
    public override double Area() => Side * Side;
}

class Program
{
    static void Main(string[] args)
    {
        List<Shape> shapes = new List<Shape> { new Circle(2), new Square(3) };

        foreach (Shape s in shapes)
        {
            Console.WriteLine(s.Area());
        }
    }
}

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Polymorphism

Polymorphism

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