Polymorphism: overloading vs overriding — OOP Concepts in C#

8. Polymorphism: overloading vs overriding

Basic★ Must knowLesson 8 of 15

Compile-time (static) polymorphism — method overloading: same name, different parameter lists, chosen by the compiler. Operator overloading is also compile-time.

Runtime (dynamic) polymorphism — method overriding: a virtual/abstract base method replaced with override in a derived class; the actual object type decides at runtime.

csharp

public class Calculator
{
    public int Add(int a, int b) => a + b;                 // overloads
    public double Add(double a, double b) => a + b;
    public int Add(int a, int b, int c) => a + b + c;
}

List<Employee> staff = [new Permanent("Asha", 1_200_000), new Contractor("Ravi", 900, 160)];
foreach (var e in staff)
    Console.WriteLine(e.Describe());     // each object's own override runs

Method hiding (new) is different: the method chosen depends on the variable's type, not the object's.

csharp

class A { public virtual string Who() => "A"; public string Name() => "A"; }
class B : A { public override string Who() => "B"; public new string Name() => "B"; }
A x = new B();
Console.WriteLine(x.Who());   // B  (override — runtime type)
Console.WriteLine(x.Name());  // A  (hiding — compile-time type)