Using operator sealed with the members of the class

Question

I've found in the Troelsen's book, that operator sealed can be used on the members of the class to protect virtual methods from the override .

But if I don't want to override a virtual methods, what sense to make it virtual ?

Answer 1

You might have a situation like this:

public class A
{
    public virtual void MyMethod()
    {
        //...
    }
}


public class B : A
{
    public override void MyMethod()
    {
        //...
    }
}


public class C : B
{
    public override void MyMethod()
    {
        //...
    }
}

But what if you want for the inheriting class C NOT to be able to override B 's MyMethod , while still allowing B to override A 's? Then you can do:

public class B : A
{
    public sealed override void MyMethod()
    {
        //...
    }
}

With this change made, you can no longer override the method in C .

Answer 2

In this context, consider the following example:

public class A
{
    public virtual void SomeMethod() { }
}

public class B : A
{
    public sealed override void SomeMethod() { }
}

public class C : B
{
    public override void SomeMethod() { }
}

In this example, without the use of the sealed keyword on SomeMethod in class B , class C would be able to override it because it's original declaration was as virtual . The sealed keyword in this context generates a compiler error. See the MSDN for more information .