与 override 关联的密封关键字

Question

Is it always necessary to follow the sealed keyword with override in the signature of a method like the below code:

public sealed override string Method1(){.....}

I mean, if I want to "seal" the method within the base class without overriding, is the override keyword still necessary?

Answer 1

Sealing a method only makes sense if you override it.

What happens here is the following:
You are overriding a method from a base class ( override ) and tell the compiler that classes derived from your class are no longer allowed to override this method ( sealed ).

If the method is a new one declared by you in your class and you want to prevent derived classes from overriding it, simply don't declare it as virtual.

If the method is declared in a base class but is not overridable sealing it wouldn't make any sense, because it already can't be overriden.

Answer 2

I think Mr. Hilgarth has provided the best answer here , but just to add something new for programmers who have a previous background in (like myself), I think most programmers new to C#, tend to confuse sealed with final in Java with respect to overriding.

In , the default behaviour without specifying "any" modifier is that the method be overriden in its derived classes.

While in , the default behaviour is that the method be overriden unless explicitly specified using the virtual keyword.

Hope this helps to supplement the best answer above.

Answer 3

Is it always necessary to follow the sealed keyword with override in the signature of a method like the below code:

public sealed override string Method1(){.....}

I mean, if I want to "seal" the method within the base class without overriding, is the override keyword still necessary?

Answer 4

Well, it technically is possible.... however, the solution is in my option kinda dirty.

Imagine having a class A (either in your code base or an external library):

public class A
{
    public virtual void M () { /* implementation */ }
}

You could define an (abstract) class B: A as follows:

public class B : A
{
    public sealed override void M() => base.M();
}

Any class C: B would not be able to override AM as you have sealed the method (even though you made no semantic changes).