C# 0 The Complete Reference

PART I

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PART IPART I

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Current count: 10

Each time that an object of type 

CountInst

 is created, the 

static

 field 

count

 is incremented. 

Each time an object is recycled, 

count

 is decremented. Thus, 

count

 always contains a count of 

the number of objects currently in existence. This is possible only through the use of a 

static

field. There is no way for an instance variable to maintain the count because the count relates 

to the class as a whole, not to a specific instance.

Here is one more example that uses 

static

. Earlier in this chapter, you saw how a class 

factory could be used to create objects. In that example, the class factory was a non-

static

method, which meant that it could be called only through an object reference. This meant 

that a default object of the class needed to be created so that the factory method could be 

called. However, a better way to implement a class factory is as a 

static

 method, which 

allows the class factory to be called without creating an unnecessary object. Here is the 

class factory example rewritten to reflect this improvement:

// Use a static class factory.

using System;

class MyClass {

  int a, b;

  // Create a class factory for MyClass.

  static public MyClass Factory(int i, int j) {

    MyClass t = new MyClass();

    t.a = i;

    t.b = j;

    return t; // return an object

  }

  public void Show() {

    Console.WriteLine("a and b: " + a + " " + b);

  }

}

class MakeObjects {

  static void Main() {

    int i, j;

    // Generate objects using the factory.

    for(i=0, j=10; i < 10; i++, j--) {

      MyClass ob = MyClass.Factory(i, j); // get an object

      ob.Show();

    }

    Console.WriteLine();

  }

}

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In this version, 

Factory( )

 is invoked through its class name in this line of code:

MyClass ob = MyClass.Factory(i, j); // get an object

There is no need to create a 

MyClass

 object prior to using the factory.