STATIC MEMBER …………….

STATIC MEMBER …………….
A C# class can contain both static and non-static members. When we declare a member with the help of the keyword static, it becomes a static member. A static member belongs to the class rather than to the objects of the class. Hence static members are also known as class members and non-static members are known as instance members.

In C#, data fields, member functions, properties and events can be declared either as static or non-static. Remember that indexers in C# can't declared as static.

Static Fields

Static fields can be declared as follows by using the keyword static.

class My Class
{
public static int x;
public static int y = 20;
}

When we declare a static field inside a class, it can be initialized with a value as shown above. All un-initialized static fields automatically get initialized to their default values when the class is loaded first time.
For example


// C#:static & non-static
// Author: rajeshvs@msn.com
using System;
class MyClass
{
public static int x = 20;
public static int y;
public static int z = 25;
public MyClass(int i)
{
x = i;
y = i;
z = i;
}
}
class MyClient
{
public static void Main()
{
Console.WriteLine("{0},{1},{2}",MyClass.x,MyClass.y,MyClass.z);
MyClass mc = new MyClass(25);

Console.WriteLine("{0},{1},{2}",MyClass.x,MyClass.y,MyClass.z);
}
}

The C# provides a special type of constructor known as static constructor to initialize the static data members when the class is loaded at first. Remember that, just like any other static member functions, static constructors can't access non-static data members directly.
The name of a static constructor must be the name of the class and even they don't have any return type. The keyword static is used to differentiate the static constructor from the normal constructors. The static constructor can't take any arguments. That means there is only one form of static constructor, without any arguments. In other way it is not possible to overload a static constructor.

We can't use any access modifiers along with a static constructor.

// C# static constructor
// Author: rajeshvs@msn.com
using System;
class MyClass
{
public static int x;
public static int y;
static MyClass ()
{
x = 100;
Y = 200;
}
}
class MyClient
{
public static void Main()
{
Console.WriteLine("{0},{1},{2}",MyClass.x,MyClass.y);
}
}

Note that static constructor is called when the class is loaded at the first time. However we can't predict the exact time and order of static constructor execution. They are called before an instance of the class is created, before a static member is called and before the static constructor of the derived class is called.
Static Member Functions

Inside a C# class, member functions can also be declared as static. But a static member function can access only other static members. They can access non-static members only through an instance of the class.

We can invoke a static member only through the name of the class. In C#, static members can't invoked through an object of the class as like in C++ or JAVA.

// C#:static & non-static
// Author: rajeshvs@msn.com

using System;
class MyClass
{
private static int x = 20;
private static int y = 40;
public static void Method()
{
Console.WriteLine("{0},{1}",x,y);
}
}
class MyClient
{
public static void Main()
{
MyClass.Method();

}
}

Static Properties

The properties also in C# can be declared as static. The static properties are accessing using the class name. A concrete example is shown below.

// C#:static & non-static
// Author: rajeshvs@msn.com

using System;
class MyClass
{
public static int X
{
get
{
Console.Write("GET");
return 10;
}
set
{
Console.Write("SET");
}
}

}
class MyClient
{
public static void Main()
{
MyClass.X = 20; // calls setter displays SET
int val = MyClass.X;// calls getter displays GET
}
}

Static Indexers
In C# there is no concept of static indexers, even though static properties are there.

Static Members & Inheritance

A derived class can inherit a static member. The example is shown below.

// C#:static
// Author: rajeshvs@msn.com
using System;
class MyBase
{
public static int x = 25;
public static void Method()
{
Console.WriteLine("Base static method");
}

}
class MyClass : MyBase
{
}
class MyClient
{
public static void Main()
{
MyClass.Method(); // Displays 'Base static method'
Console.WriteLine(MyClass.x);// Displays 25
}
}

But a static member in C# can't be marked as override, virtual or abstract. However it is possible to hide a base class static method in a derived class by using the keyword new.
An example is shown below.

// C#:static & non-static
// Author: rajeshvs@msn.com

using System;
class MyBase
{
public static int x = 25;
public static void Method()
{
Console.WriteLine("Base static method");
}

}
class MyClass : MyBase
{
public new static int x = 50;
public new static void Method()
{
Console.WriteLine("Derived static method");
}
}
class MyClient
{
public static void Main()
{
MyClass.Method(); // Displays 'Derived static method'
Console.WriteLine(MyClass.x);// Displays 50
}
}

Finally remember that it is not possible to use this to reference static methods.

>> Static variables inside a class method (not in a class) shared among all instances of the class?
>>Even if you have a bunch of instances of this class, you only will have one copy of your static variable shared by all the instances

any variable marked as a static is considered a variable owned by the class. Even if you have a bunch of instances of this class, you only will have one copy of your static variable shared by all the instances.

This is the main difference with instance variables where each instance of your class have his own variables.

Example, if you have a class like this:

public class SoldCar{
public String model; //instance variable - each soldCar have its model
public int cost; //instance variable - each soldCar have its cost
public static int count; //class variable - all soldCars share this count

public SoldCar(){
count ++;
}

public static void main(String[] args){
SoldCar ferrari = new SoldCar();
ferrari.model = "fiorano";
ferrari .cost = 999999;

SoldCar beetle = new SoldCar();
beetle.model = "new beetle";
beetle.cost = 2222;

System.out.println( ferrari.model + "," + ferrari.count );
System.out.println( beetle.model + "," + beetle.count );
}

}

The output of this program is :
fiorano,2
new beetle,2


You can declare a static local variable in a class, that is, inside a procedure in that class. However, you cannot declare a static local variable in a structure.


We use static class when we have to separate data and behavior that will be independent of any object identity. The data and functions do not change regardless of what happens to the object.
A static class can only contain static members. We cannot create an instance of a static class. Static class is always sealed and they cannot contain instance constructor. Hence we can also say that creating a static class is nearly same as creating a class with only static members and a private constructor (private constructor prevents the class from being instantiated).
The advantage of using the static class is that compiler can check that no instance of the class is accidentally added. The complier will not allow any instance class of a static class. We also cannot inherit a static class since it is sealed. Static class do not have constructor, but can still declare static constructor to set up the initial values.
Static class also makes the implementation simpler and faster since we do not have make and instance of the class to call its method. An example of good use of static class would be a class like math, which does all the mathematic function, or a currency converter class to convert currency class for converting the currency.