C# 0 The Complete Reference

static

 method. 

However, the use of 

Val

 is okay since it is a 

static

 variable.

The same problem occurs when trying to call a non-

static

 method from within a 

static

method of the same class. For example:

using System;

class AnotherStaticError {

  // A non-static method.

  void NonStaticMeth() {

     Console.WriteLine("Inside NonStaticMeth().");

  }

  /* Error! Can't directly call a non-static method

     from within a static method. */

  static void staticMeth() {

    NonStaticMeth(); // won't compile

  }

}

In this case, the attempt to call a non-

static

 (that is, instance method) from a 

static

 method 

causes a compile-time error.

It is important to understand that a 

static

 method 

can

 call instance methods and access 

instance variables of its class if it does so through an object of that class. It is just that it 

cannot use an instance variable or method without an object qualification. For example, 

this fragment is perfectly valid:

class MyClass {

  // A non-static method.

  void NonStaticMeth() {

     Console.WriteLine("Inside NonStaticMeth().");

  }

  /* Can call a non-static method through an

     object reference from within a static method. */

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  public static void staticMeth(MyClass ob) {

    ob.NonStaticMeth(); // this is OK

  }

}

Here, 

NonStaticMeth( )

 is called by 

staticMeth( )

 through 

ob

, which is an object of type 

MyClass

.

Because

static

 fields are independent of any specific object, they are useful when you 

need to maintain information that is applicable to an entire class. Here is an example of 

such a situation. It uses a 

static

 field to maintain a count of the number of objects that are 

in existence.

// Use a static field to count instances.

using System;

class CountInst {

  static int count = 0;

  // Increment count when object is created.

  public CountInst() {

    count++;

  }

  // Decrement count when object is destroyed.

  ~CountInst() {

    count--;

  }

  public static int GetCount() {

    return count;

  }

}

class CountDemo {

  static void Main() {

    CountInst ob;

    for(int i=0; i < 10; i++) {

      ob = new CountInst();

      Console.WriteLine("Current count: " + CountInst.GetCount());

    }

  }

}

The output is shown here:

Current count: 1

Current count: 2

Current count: 3

Current count: 4

Current count: 5

Current count: 6

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