Csharp/CSharp Tutorial/Class/static field

Instance Counting

<source lang="csharp">using System.ruponentModel;

   public class MainClass
   {
       public string Name { get; private set; }
       public int Age { get; private set; }
       private static int InstanceCounter { get; set; }
       private static readonly object counterLock = new object();
       public MainClass(string name, int age)
       {
           Name = name;
           Age = age;
           lock (counterLock)
           {
               InstanceCounter++;
           }
       }
   }</source>

Reference a static member variable without using the class name

<source lang="csharp">public class Employee {

  public Employee()
  {
     totalHeadCount = 123;
     Employee.totalHeadCount = 456;
  }
  public static int totalHeadCount;

} public class MainClass {

  static void Main()
  {
     Employee bob = new Employee();
     
     System.Console.WriteLine("Static Field Employee.totalHeadCount is {0}",Employee.totalHeadCount );
  }

}</source>

Static Field Employee.totalHeadCount is 456

Reference Static Field without Instance

<source lang="csharp">using System; class MyClass {

  static public int myStaticValue;

} class Program {

  static void Main()
  {
     MyClass.myStaticValue = 5;
     Console.WriteLine("myStaticValue = {0}", MyClass.myStaticValue);
  }

}</source>

myStaticValue = 5

Static field init

<source lang="csharp">using System; public class MyClass {

  private static int InitX()
  {
     Console.WriteLine( "MyClass.InitX()" );
     return 1;
  }
  private static int InitY()
  {
     Console.WriteLine( "MyClass.InitY()" );
     return 2;
  }
  private static int InitA()
  {
     Console.WriteLine( "MyClass.InitA()" );
     return 3;
  }
  private static int InitB()
  {
     Console.WriteLine( "MyClass.InitB()" );
     return 4;
  }
  private int y = InitY();
  private int x = InitX();
  private static int a = InitA();
  private static int b = InitB();

} public class MainClass {

  static void Main()
  {
     MyClass a = new MyClass();
  }

}</source>

MyClass.InitA()
MyClass.InitB()
MyClass.InitY()
MyClass.InitX()

Static Fields

1. A static member can be accessed before any objects of its class are created.
2. You can call a static member without referencing to any object.
3. You can declare both static methods and static variables.
4. Variables declared as static are, essentially, global variables.
5. All instances of the class share the same static variable.
6. A static variable is initialized when its class is loaded.
7. A static variable always has a value.
8. If not initialized, a static variable is initialized to zero for numeric values.
9. If not initialized, a static variable is initialized to null for object references.
10. If not initialized, a static variable is initialized to false for variables of type bool.

<source lang="csharp">using System; class MyClass {

   public MyClass()
   {
       instanceCount++;
   }
   public static int instanceCount = 0;

} class MainClass {

   public static void Main()
   {
       MyClass my = new MyClass();
       Console.WriteLine(MyClass.instanceCount);
       MyClass my2 = new MyClass();
       Console.WriteLine(MyClass.instanceCount);
   }

}</source>

1
2

Use a static constructor.

<source lang="csharp">using System;

class Cons {

 public static int a; 
 public int b; 

 // static constructor 
 static Cons() { 
   a = 99; 
   Console.WriteLine("Inside static constructor."); 
 } 

 // instance constructor 
 public Cons() { 
   b = 100; 
   Console.WriteLine("Inside instance constructor."); 
 } 

}

class MainClass {

 public static void Main() {   
   Cons ob = new Cons(); 

   Console.WriteLine("Cons.a: " + Cons.a); 
   Console.WriteLine("ob.b: " + ob.b); 
 } 

}</source>

Inside static constructor.
Inside instance constructor.
Cons.a: 99
ob.b: 100

Use a static field to count instances.

<source lang="csharp">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 MainClass {

 public static void Main() { 
   CountInst ob; 


   for(int i=0; i < 10; i++) { 
     ob = new CountInst(); 
     Console.WriteLine("Current count: " +  
                       CountInst.getcount()); 
   } 

 }  

}</source>

Current count: 1
Current count: 2
Current count: 3
Current count: 4
Current count: 5
Current count: 6
Current count: 7
Current count: 8
Current count: 9
Current count: 10