virtual and override methods

Context: virtual allows a method to be overridden in a derived class. override provides a new implementation.

Rules

• A virtual method may have an implementation.
• An override method must match the signature.
• You cannot override a non‑virtual or static method.

public class Shape
{
    public virtual double Area() => 0;
}
public class Circle : Shape
{
    private double _radius;
    public Circle(double r) => _radius = r;
    public override double Area() => Math.PI * _radius * _radius;
}

Calling Overridden Methods

Runtime polymorphism: the actual object type determines which method is called.

Shape shape = new Circle(5);
Console.WriteLine(shape.Area()); // uses Circle's Area

Override vs new

override replaces the base method; new hides it (see 4.3.6).