使用与班级成员密封的运算符

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 .