C# Language Specification

Sealed methods

When an instance method declaration includes a sealed modifier, that method is said to be a sealed method. If an instance method declaration includes the sealed modifier, it must also include the override modifier. Use of the sealed modifier prevents a derived class from further overriding the method.

The example

using System;

class A
{

public virtual void F() {
Console.WriteLine("A.F");
}

public virtual void G() {

Console.WriteLine("A.G");
}
}

class B: A

{
sealed override public void F() {
Console.WriteLine("B.F");
}

override public void G() {

Console.WriteLine("B.G");
}
}

class C: B

{
override public void G() {
Console.WriteLine("C.G");
}
}

the class B provides two override methods: an F method that has the sealed modifier and a G method that does not. B’s use of the sealed modifier prevents C from further overriding F.

6.