C# Polymorphism

Question

What's the difference between run-time polymorphism and compile-time polymorphism? Also, what's the difference between early binding and late binding? Examples would be highly appreciated.

Answer 1

Compile Time Polymorphism

Method overloading is a great example. You can have two methods with the same name but with different signatures. The compiler will choose the correct version to use at compile time.

Run-Time Polymorphism

Overriding a virtual method from a parent class in a child class is a good example. Another is a class implementing methods from an Interface. This allows you to use the more generic type in code while using the implementation specified by the child. Given the following class definitions:

public class Parent
{
    public virtual void SayHello() { Console.WriteLine("Hello World!"); }
}

public class Child : Parent
{
    public override void SayHello() { Console.WriteLine("Goodbye World!"); }
}

The following code will output "Goodbye World!":

Parent instance = new Child();
instance.SayHello();

Early Binding

Specifying the type at compile time:

SqlConnection conn = new SqlConnection();

Late Binding

The type is determined at runtime:

object conn = Activator.CreateInstance("System.Data.SqlClient.SqlConnection");