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  

317

PART IPART I

  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;

  }

}

// Use ISeries to implement a series of prime numbers.

class Primes : ISeries {

  int start;

  int val;

  public Primes() {

    start = 2;

    val = 2;

  }

  public int GetNext() {

    int i, j;

    bool isprime;

    val++;

    for(i = val; i < 1000000; i++) {

      isprime = true;

      for(j = 2; j <= i/j; j++) {

        if((i%j)==0) {

          isprime = false;

          break;

        }

      }

      if(isprime) {

        val = i;

        break;

      }

    }

    return val;

  }

  public void Reset() {

    val = start;

  }

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318

 

P a r t   I :  

T h e   C #   L a n g u a g e

  public void SetStart(int x) {

    start = x;

    val = start;

  }

}

class SeriesDemo2 {

  static void Main() {

    ByTwos twoOb = new ByTwos();

    Primes primeOb = new Primes();

    ISeries ob;

    for(int i=0; i < 5; i++) {

      ob = twoOb;

      Console.WriteLine("Next ByTwos value is " +

                          ob.GetNext());

      ob = primeOb;

      Console.WriteLine("Next prime number is " +

                          ob.GetNext());

    }

  }

}

The output from the program is shown here:

Next ByTwos value is 2

Next prime number is 3

Next ByTwos value is 4

Next prime number is 5

Next ByTwos value is 6

Next prime number is 7

Next ByTwos value is 8

Next prime number is 11

Next ByTwos value is 10

Next prime number is 13

In

Main( )

,

ob

 is declared to be a reference to an 

ISeries

 interface. This means that it can be 

used to store references to any object that implements 

ISeries

. In this case, it is used to refer 

to

twoOb

 and 

primeOb

, which are objects of type 

ByTwos

 and 

Primes

, respectively, which 

both implement 

ISeries

.

One other point: An interface reference variable has knowledge only of the methods 

declared by its 

interface

 declaration. Thus, an interface reference cannot be used to access 

any other variables or methods that might be supported by the object.

Interface Properties

Like methods, properties are specified in an interface without any body. Here is the general 

form of a property specification:

// interface property

type name

 {

   get;

   set;

}

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