A class represents a concept within the system being modeled. It is an abstraction of a set of objects with the same attributes, operations, relationships, and semantics.
An interface is a specifier for the externally-visible operations of a class, component, or subsystem. Often, interfaces specify only a limited part of the behavior of an actual class.
Related Topics:
Creating Classes and Interfaces
Editing Classes and Interfaces
Working with Inner Classes and Interfaces