passage in a book

[Guest]

hi,

i was reading a vb.net book that said the following regarding:

Interfaces allow you to program using methods on the interface rather than
methods on the object?

How is this a benefit in lamen's terms?

thanks,
mj

 

[Marina]

It basically means that it allows you to look at the object in terms of its
interface - and thus be guaranteed that it has a particular method.

So let's say you have classes A, B, C. You will have a collection of
objects, and each object in the collection will be an instance of one of
those. You can either:
a) Look at each object in the collection, figure out if it's an A, B or C.
Then cast it to the right type, and call method DoSomething on it
b) Make each class implement ISomeInterface which has a method DoSomething.
Then just cast each object to an ISomeInterface and call DoSomething.

Which is easier?

Consider down the road, you add a class D. Scenario 'a', you would have to
change the code for your collection to now deal with a class D. Scenario
'b', you don't need to do anything, as long as class D implements
ISomeInterface.

 

[Guest]

thanks for the explanation. what do you mean when you said:

Then just cast each object to an ISomeInterface and call DoSomething.

how would the syntax look for that line?

mj

 

[Marina]

(ISomeInterface)myObj where myObj is some object that you have that
implements this interface. Otherwise, this code would throw an exception.

 

[Phill. W]

Or, perhaps more relevantly to ...dotnet.languages.*vb* :

DirectCast( myObj, ISomeInterface )

unless you know something we don't ... ;-)

Regards,
Phill W.

 

[Guest]

Thank you very much. this helped a lot.

Or, perhaps more relevantly to ...dotnet.languages.*vb* :

DirectCast( myObj, ISomeInterface )

unless you know something we don't ... ;-)

Regards,
Phill W.

 

[Guest]

Would this be along the same lines as APIs?

It basically means that it allows you to look at the object in terms of its
interface - and thus be guaranteed that it has a particular method.

So let's say you have classes A, B, C. You will have a collection of
objects, and each object in the collection will be an instance of one of
those. You can either:
a) Look at each object in the collection, figure out if it's an A, B or C.
Then cast it to the right type, and call method DoSomething on it
b) Make each class implement ISomeInterface which has a method DoSomething.
Then just cast each object to an ISomeInterface and call DoSomething.

Which is easier?

Consider down the road, you add a class D. Scenario 'a', you would have to
change the code for your collection to now deal with a class D. Scenario
'b', you don't need to do anything, as long as class D implements
ISomeInterface.