Base on the documentation and sample code that I have gone through, I got an impression that when a class defined in xcode is read into and configured in Interface Builder, an object based on the class is effectively created and stored in an xib or nib file. So the object is ready to be used when the corresponding application is launched.

Alternatively, for classes that have not been handled by Interface Builder, code such as the "new" statements have to be written in xcode explicitly in order for the associated objects to be created and used.

It will be very nice to have people who are more knowledgable than me to confirm or to correct my very naive understanding of Interface Builder ...