C# 0 The Complete Reference

PART I

C h a p t e r   1 2 :  

I n t e r f a c e s ,   S t r u c t u r e s ,   a n d   E n u m e r a t i o n s  

313

PART IPART I

The methods that implement an interface must be declared 

public

. The reason for this is 

that methods are implicitly public within an interface, so their implementation must also be 

public. Also, the return type and signature of the implementing method must match exactly 

the return type and signature specified in the 

interface

 definition.

Here is an example that implements the 

ISeries

 interface shown earlier. It creates a class 

called

ByTwos

, which generates a series of numbers, each two greater than the previous one.

// Implement ISeries.

class ByTwos : ISeries {

  int start;

  int val;

  public ByTwos() {

    start = 0;

    val = 0;

  }

  public int GetNext() {

    val += 2;

    return val;

  }

  public void Reset() {

    val = start;

  }

  public void SetStart(int x) {

    start = x;

    val = start;

  }

}

As you can see, 

ByTwos

 implements all three methods defined by 

ISeries

. As explained, 

this is necessary since a class cannot create a partial implementation of an interface.

Here is a class that demonstrates 

ByTwos

:

// Demonstrate the ByTwos interface.

using System;

class SeriesDemo {

  static void Main() {

    ByTwos ob = new ByTwos();

    for(int i=0; i < 5; i++)

      Console.WriteLine("Next value is " +

                         ob.GetNext());

    Console.WriteLine("\nResetting");

    ob.Reset();

    for(int i=0; i < 5; i++)

      Console.WriteLine("Next value is " +

                         ob.GetNext());

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    Console.WriteLine("\nStarting at 100");

    ob.SetStart(100);

    for(int i=0; i < 5; i++)

      Console.WriteLine("Next value is " +

                         ob.GetNext());

  }

}

To compile 

SeriesDemo

, you must include the files that contain