Interfaces

Would someone please give me an example of real world use of interfaces.
Here is what is confusing me. Say I have one dll that has one class called
Messenger and one function called SendMessage. If I suspect that the
implementation of SendMessage may change should I include an interface
(IMessenger) into the dll that defines the SendMessage function? Then have
the class implement it? If I do then should a client call the dll like this:

....
IMessenger obj = new Messenger();
obj.SendMessage();
....

Now if I add a new class (Messenger2) to the dll that implements the
IMyClass interface with different implementation than MyClass, I will still
have to change all my client code to:

....
IMyClass obj = new Messenger2();
obj.SendMessage();
....

If I am using interfaces correctly I fail to see how they are useful. Any
help would be appreciated.

You should use interfaces or abstract or super classes when ever possible.
You just need to figure out which is the right one to use.

Here is a really world example - I am doing this. I need to create functions
that add, multiply, divide, concat, convert, etc. At design time (not coding
but a GUI tool that allows someone to assign parameters to the functions)
I care what the function does. At run time I don't. I want to be able to
loop through all the functions at run time and just say Function.Evaluate()
and get an object back. I also need to add functions in the future that
I currently don't know about or don't want to implement till needed.

So I have an interface called Function (actually an abstract class but don't
let that distract you) that has an Evaluate Method that returns an Object.

The AddFunction implements this method and takes to numerical objects and
adds them and returns a numerical Object.

The ConcatFunction takes to Objects and Concats them and returns a String
Object.

And so on.

Does this help? I have more. What is really cool is that these functions
also implement another interface and they are treated as a completely different
object type. This would have been impossible to do or at least involve completely
crazy coding in a non OO language - even VB.

Mark




"o11011" <o11011@hotmail.com> wrote:
>Would someone please give me an example of real world use of interfaces.
>Here is what is confusing me. Say I have one dll that has one class called
>Messenger and one function called SendMessage. If I suspect that the
>implementation of SendMessage may change should I include an interface
>(IMessenger) into the dll that defines the SendMessage function? Then have
>the class implement it? If I do then should a client call the dll like this:
>
>....
>IMessenger obj = new Messenger();
>obj.SendMessage();
>....
>
>Now if I add a new class (Messenger2) to the dll that implements the
>IMyClass interface with different implementation than MyClass, I will still
>have to change all my client code to:
>
>....
>IMyClass obj = new Messenger2();
>obj.SendMessage();
>....
>
>If I am using interfaces correctly I fail to see how they are useful. Any
>help would be appreciated.
>
>

Some sample code might help clear this up.Is my example a good use of
interface? Is yes then how do I write the client so I don't have to change
it when I add the new class?

Thanks so far it is getting clearer.

"MarkN" <m@n.com> wrote in message news:3c920c6c$1@10.1.10.29...
>
> You should use interfaces or abstract or super classes when ever possible.
> You just need to figure out which is the right one to use.
>
> Here is a really world example - I am doing this. I need to create
functions
> that add, multiply, divide, concat, convert, etc. At design time (not
coding
> but a GUI tool that allows someone to assign parameters to the functions)
> I care what the function does. At run time I don't. I want to be able to
> loop through all the functions at run time and just say
Function.Evaluate()
> and get an object back. I also need to add functions in the future that
> I currently don't know about or don't want to implement till needed.
>
> So I have an interface called Function (actually an abstract class but
don't
> let that distract you) that has an Evaluate Method that returns an Object.
>
> The AddFunction implements this method and takes to numerical objects and
> adds them and returns a numerical Object.
>
> The ConcatFunction takes to Objects and Concats them and returns a String
> Object.
>
> And so on.
>
> Does this help? I have more. What is really cool is that these functions
> also implement another interface and they are treated as a completely
different
> object type. This would have been impossible to do or at least involve
completely
> crazy coding in a non OO language - even VB.
>
> Mark
>
>
>
>
> "o11011" <o11011@hotmail.com> wrote:
> >Would someone please give me an example of real world use of interfaces.
> >Here is what is confusing me. Say I have one dll that has one class
called
> >Messenger and one function called SendMessage. If I suspect that the
> >implementation of SendMessage may change should I include an interface
> >(IMessenger) into the dll that defines the SendMessage function? Then
have
> >the class implement it? If I do then should a client call the dll like
this:
> >
> >....
> >IMessenger obj = new Messenger();
> >obj.SendMessage();
> >....
> >
> >Now if I add a new class (Messenger2) to the dll that implements the
> >IMyClass interface with different implementation than MyClass, I will
still
> >have to change all my client code to:
> >
> >....
> >IMyClass obj = new Messenger2();
> >obj.SendMessage();
> >....
> >
> >If I am using interfaces correctly I fail to see how they are useful. Any
> >help would be appreciated.
> >
> >
>

You use interfaces when you're not sure what classes you're going to use at
runtime, but you do know how you're going to use them.

For example, the frameworks support the IComparable interface, which has a
CompareTo() method in this. Because they've used an interface, both array
and ArrayList can now have a generic Sort() function; it just takes whatever
object it has, casts it to IComparable, and calls the function.



--
This posting is provided "AS IS" with no warranties, and confers no rights.

"o11011" <o11011@hotmail.com> wrote in message news:3c920571$1@10.1.10.29...
> Would someone please give me an example of real world use of interfaces.
> Here is what is confusing me. Say I have one dll that has one class called
> Messenger and one function called SendMessage. If I suspect that the
> implementation of SendMessage may change should I include an interface
> (IMessenger) into the dll that defines the SendMessage function? Then have
> the class implement it? If I do then should a client call the dll like
this:
>
> ...
> IMessenger obj = new Messenger();
> obj.SendMessage();
> ...
>
> Now if I add a new class (Messenger2) to the dll that implements the
> IMyClass interface with different implementation than MyClass, I will
still
> have to change all my client code to:
>
> ...
> IMyClass obj = new Messenger2();
> obj.SendMessage();
> ...
>
> If I am using interfaces correctly I fail to see how they are useful. Any
> help would be appreciated.
>
>

I would suggest getting a book on Design Patterns (or search the web for
'GOF design patterns) - study the Abstract Factory and Factory Method
discussions for a solid background in the use of interfaces.


--
Turn on, tune in, download.
zane@mabry.com

Thank you all.

"o11011" <o11011@hotmail.com> wrote in message news:3c920571$1@10.1.10.29...
> Would someone please give me an example of real world use of interfaces.
> Here is what is confusing me. Say I have one dll that has one class called
> Messenger and one function called SendMessage. If I suspect that the
> implementation of SendMessage may change should I include an interface
> (IMessenger) into the dll that defines the SendMessage function? Then have
> the class implement it? If I do then should a client call the dll like
this:
>
> ...
> IMessenger obj = new Messenger();
> obj.SendMessage();
> ...
>
> Now if I add a new class (Messenger2) to the dll that implements the
> IMyClass interface with different implementation than MyClass, I will
still
> have to change all my client code to:
>
> ...
> IMyClass obj = new Messenger2();
> obj.SendMessage();
> ...
>
> If I am using interfaces correctly I fail to see how they are useful. Any
> help would be appreciated.
>
>

o11011,

"o11011" <o11011@hotmail.com> wrote in message news:3c92d7e3$1@10.1.10.29...
> Thank you all.
>

In addition to the responses you already got, another example for using
interfaces is the remoting problem you asked about.

Michael