C# 0 The Complete Reference

ByTwos

 and 

Primes

 generate completely unrelated 

series of numbers, both implement 

ISeries

. As explained, an interface says nothing about 

the implementation, so each class is free to implement the interface as it sees fit.

Using Interface References

You might be somewhat surprised to learn that you can declare a reference variable of an 

interface type. In other words, you can create an interface reference variable. Such a variable 

can refer to any object that implements its interface. When you call a method on an object 

through an interface reference, it is the version of the method implemented by the object 

that is executed. This process is similar to using a base class reference to access a derived 

class object, as described in Chapter 11.

The following example illustrates the use of an interface reference. It uses the same 

interface reference variable to call methods on objects of both 

ByTwos

 and 

Primes

. For 

clarity, it shows all pieces of the program, assembled into a single file.

// Demonstrate interface references.

using System;

// Define the interface.

public interface ISeries {

  int GetNext(); // return next number in series

  void Reset(); // restart

  void SetStart(int x); // set starting value

}

// Use ISeries to implement a series in which each

// value is two greater than the previous one.

class ByTwos : ISeries {

  int start;

  int val;

www.freepdf-books.com

---