query on c#4 interfaces

I have just been reading:
http://www.daniweb.com/software-development/csharp/threads/114364

At the bottom is the following:

Interface in object answer to one simple requirement facilitate mostly used functionality
you whant to give only what is use full to the user so using your object become simpler
if your class offer 40 functionality and one of your user commonly uses 3 of theme you dont whant to show him all of them it create noise. take an oo course.

Say for argument sake I did have a class with 40 functions on and only wanted to expose 3.

Is it the case that I need to create an interface that only has 3 function declarations and then create a new class which implements that interface or....?

Wouldn;t that mean ending up with a lot of sub version of the main class?

Excuse the stupid question still trying to get using interfaces straight in my head.

Thanks
scm0smlAsked:
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käµfm³d 👽Commented:
I don't know that I necessarily agree with using interfaces for the sole purpose of member hiding--though I suppose you could. An interface is really more like a contract. You are telling other code:  "Hey, I offer you these services and/or data." Using interfaces is also a way to get around .NET's single-inheritance behavior--you can inherit only one class, but you can implement n interfaces.

To answer your specific question, yes, you would create the interface that only has the 3 methods. This doesn't really hide anything, though. If I know the type of the object implementing the interface, then I can simply cast the object to that type and voila!, I have access to the public members again.
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scm0smlAuthor Commented:
Right ok great thanks for that.
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Kyle AbrahamsSenior .Net DeveloperCommented:
some good articles:
http://www.4guysfromrolla.com/articles/110304-1.aspx

http://msdn.microsoft.com/en-us/library/ms229013.aspx

In terms of hiding code I would make the 3 public and the rest private . . . no need to create an interface for that.
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