Inheritance

[tshad]

I am playing with Inheritance and want to make sure I understand it.

I have the following Classes:
*******************************************
Public Class AuthHeader:Inherits SoapHeader
Public AuthHeaderName As String
Public SessionKey As String = "Default"
End Class

Public Class ServiceTicket:Inherits AuthHeader
Public IsAuthenticated As Boolean
Public SessionKey As String = "Default from ServiceTicket"
Public Expiration As DateTime
End Class

Public Class TempClass1:Inherits ServiceTicket
Public TomsClass1Name As String
End Class
*****************************************

I assume that inheritance depends on the order of definition.

Here SessionKey is being defined in 2 classes. For TempClass1 and
ServiceTicket, Session would be "Default from ServiceTicket" since it would
have been defined second. So if I create TempClass1, it would work
something like, SessionKey would first be "Default" but then ServiceTicket
would re-define it, since it inherited it (and is higher up the chain) and
change it to "Default from ServiceTicket".

In this case, if I had:

Dim objTempClass1 As new TempClass1
Dim objServiceTicket As new ServiceTicket
Dim objAuthHeader As new AuthHeader

objTempClass1.SessionKey = "Default from ServiceTicket" '
Inherited from ServiceKey
objServiceKey.SessionKey = "Default from ServiceTicket"
objAuthHeader.SessionKey = "Default"

But if I took out the Sessionkey from the ServiceKey class that it would be:

objTempClass1.SessionKey = "Default" ' Inherited from
AuthHeader
objServiceKey.SessionKey = "Default" ' Inherited
from AuthHeader
objAuthHeader.SessionKey = "Default"

Also, I originally got this from a sample program that didn't set the
defaults, but had it defined as:
*******************************************
Public Class AuthHeader:Inherits SoapHeader
Public AuthHeaderName As String
Public SessionKey As String
End Class

Public Class ServiceTicket:Inherits AuthHeader
Public IsAuthenticated As Boolean
Public SessionKey As String
Public Expiration As DateTime
End Class

Public Class TempClass1:Inherits ServiceTicket
Public TomsClass1Name As String
End Class
*****************************************

Is there any good reason to defining SessionKey again ServiceTicket?

I assume since it always would inherit from AuthHeader, it would always get
SessionKey from the inheritance. If it wanted to set SessionKey in
ServiceTicket, it could just set it by:

SessionKey = "Default"

without needing to redefine it.

Is this correct?

Thanks,

Tom

 

[Vijay]

yes the reason to override are more applicable to methods, properties yes..
if you want to additional functionality to than what is available in the
base class.. I also strongly recommend that any public variables you declare
and intended to use a property or have thought it must be overridden, given
them as property definitions its much cleaner that way

VJ

 

[tshad]

yes the reason to override are more applicable to methods, properties
yes.. if you want to additional functionality to than what is available in
the base class.. I also strongly recommend that any public variables you
declare and intended to use a property or have thought it must be
overridden, given them as property definitions its much cleaner that way

I agree.

This was just a quick example of the what I was trying to play with. I just
wanted to make sure I was understanding what was happening correctly.

I wasn't sure if there was 1 variable or 2. I assume it was 1 and the last
defined one was the one I would see.

I heard from someone else that if I wanted 2 variables I would define it as
shadows (override being the default). I would still get the last defined
one, but I could also get the one in the base class by using the base class
name with the variable. Not sure why I would need that, but I am sure there
are good reasons for it. Right now I am just trying to get the basics of
inheritance down. I understand it, I just haven't build any objects that
were inherited by another object (other than the normal system ones).

Thanks,

Tom

 

[Vijay]

Personally I will try to avoid shadows.. as much as I can.. it just causes
confusion in readability. That is what I have seen in huge projects..

Vijay