Overriding an abstract method with a virtual one

Question

I\'m trying to override an abstract method in an abstract class with a virtual method in a child class. I (assumed until now?) understand the difference between abstract and

Answer 1

An abstract method is already virtual all the way down the inheritance chain - there's no need to declare it virtual in a subclass to allow the subclass to override it - the subclass can already override it.

If you don't provide an implementation, the closest implementation (looking down the inheritance list) will be used.

Answer 2

An override method is implicitly virtual (in the sense that it can be overridden in a subclass), unless marked as sealed.

Observe:

public class FirstLevelChild1 : TopLevelParent
{
    protected override void TheAbstractMethod() { }
}

public class SecondLevelChild1 : FirstLevelChild1
{
    protected override void TheAbstractMethod() { } // No problem
}

public class FirstLevelChild2 : TopLevelParent
{
    protected sealed override void TheAbstractMethod() { }
}

public class SecondLevelChild : FirstLevelChild2
{
    protected override void TheAbstractMethod() { } 
    // Error: cannot override inherited member 
    // 'FirstLevelChild2.TheAbstractMethod()' because it is sealed
}