overriding non virtual methods, why bother with override at all then

[news.microsoft.com]

Hi,

It is possible to override a non virtual method with the "new" keyword

So how is this different from specifying a method as virtual then
providing the override keyword?

Is there any differences between these two methods of overriding?

Thanks.

 

[Nicole Calinoiu]

There is a difference, and it lies in the behaviour of objects cast down to
their base classes. For example, let's say you have a class A which has a
virtual method. Class B inherits from A and overrides the virtual method.
If you cast down an object of type B to type A and execute the overridden
method, you will be executing the implementation of the method defined by
class B. However, if the method is not virtual, and it is hidden by a new
method in class B, execution of the method against an object of type B cast
down to type A will result in execution of the class A implementation of the
method. Run the following console application to verify this for yourself:

class ConsoleDemo
{
static void Main()
{
Console.WriteLine("Working with a B object:");
B b = new B();
b.ShowOverride();
b.ShowNew();

Console.WriteLine();
Console.WriteLine("Working with a B object cast down to an A
object:");
A a = (A)b;
a.ShowOverride();
a.ShowNew();

Console.ReadLine();
}
}

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

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

class B : A
{
public override void ShowOverride()
{
Console.WriteLine("B.ShowOverride()");
}

public new void ShowNew()
{
Console.WriteLine("B.ShowNew()");
}
}

 

[Ray Hsieh (Djajadinata)]

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The difference is that when you make a method virtual, it's virtual all
the way up. When you *new* a non-virtual method, however, the base
class's version of the method is *hidden*, so up the inheritance
hierarchy, that method is still non-virtual. It is only virtual from the
class where you specify new virtual, down the inheritance chain.

news.microsoft.com wrote:

| Hi,
|
| It is possible to override a non virtual method with the "new" keyword
|
| So how is this different from specifying a method as virtual then
| providing the override keyword?
|
| Is there any differences between these two methods of overriding?
|
| Thanks.
|
|


- --
Ray Hsieh (Djajadinata)
ray underscore usenet at yahoo dot com
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[Jeff Louie]

This should help:

Chapter 8 "Shadow Fields, Override Virtual Methods" 

http://www.geocities.com/jeff_louie/OOP/oop8.htm

Regards,
Jeff

It is possible to override a non virtual method with the "new" keyword

So how is this different from specifying a method as virtual then
providing the override keyword?
Is there any differences between these two methods of overriding?<