Global Variables vs. instance variables declared at application object level

There is only one application object instance during the application runtime
that is instantiated at the start along with the global variables, so I am
looking for what are the major differences, advantages , and disadvantages
between Global Variables and instance variables declared for the application
object.

Thanks



0
Mohammad
7/9/1998 1:04:57 AM
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I've wondered also about the application instance variables.
I think the difference with global vars is very subtle. Maybe too subtle to
be of any use.

Anyway, you shouldn't be using either one of them :-)


Geert 'Darling' Van Damme


Mohammad M. Khan wrote in message ...
>There is only one application object instance during the application
runtime
>that is instantiated at the start along with the global variables, so I am
>looking for what are the major differences, advantages , and disadvantages
>between Global Variables and instance variables declared for the
application
>object.
>
>Thanks
>
>
>


0
Geert
7/9/1998 8:22:13 AM
On Wed, 8 Jul 1998 18:04:57 -0700, "Mohammad M. Khan"
<Mohammad.Khan@maisystems.com> wrote:

>There is only one application object instance during the application runtime
>that is instantiated at the start along with the global variables, so I am
>looking for what are the major differences, advantages , and disadvantages
>between Global Variables and instance variables declared for the application
>object.
>
>Thanks
>
>
>

Conceptually they are the same: A place to hold global data (that is,
data that is needed by various objects in the application).  Neither
method offers any protection against accidental change, though.  

The only advantage globals have is that you don't have to fully
qualify their path as you would with the instance variables <g>.

To implement this properly using OO concepts, you could: Keep them as
instance variables, but mark them Private.  Set and Get functions
would need to be written to allow access to and from the variables.
In this way, though, you've encapsulated the variables into the
application object and it alone controls access to the values.

These methods and more are outlined in Sybase's course, Building
Object Oriented Application with PowerBuilder.  I teach it and I
highly recommend it.

 

Larry Molter CPI, CPD-P
PowerCerv
0
lmolter1
7/9/1998 2:05:27 PM
Reply:

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