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Understanding Interface Types

To begin this chapter, allow me to provide a formal definition of the interface type. An interface is

nothing more than a named set of 

abstract members. Recall from Chapter 6 that abstract methods

are pure protocol in that they do not provide a default implementation. The specific members

defined by an interface depend on the exact behavior it is modeling. Yes, it’s true. An interface

expresses a 

behavior that a given class or structure may choose to implement. Furthermore, as you

will see in this chapter, a class (or structure) can support as many interfaces as necessary, thereby

supporting (in essence) multiple behaviors.

As you might guess, the .NET base class libraries ship with hundreds of predefined interface

types that are implemented by various classes and structures. For example, as you will see in Chap-

ter 22, ADO.NET ships with multiple data providers that allow you to communicate with a particular

database management system. Thus, unlike COM-based ADO, under ADO.NET we have numerous

connection objects we may choose between (SqlConnection, OracleConnection, OdbcConnection,

etc.).

Regardless of the fact that each connection object has a unique name, is defined within a dif-

ferent namespace, and (in some cases) is bundled within a different assembly, all connection

objects implement a common interface named IDbConnection: