static (C# Reference)
The static modifier can be used with classes, fields, methods, properties, operators, events, and constructors, but it cannot be used with indexers, destructors, or types other than classes. The static modifier on a class means that the class cannot be instantiated, and that all of its members are static. A static member has one version regardless of how many instances of its enclosing type are created. For more information, see Static Classes and Static Class Members (C# Programming Guide).
Example
The following class is declared as static and contains only static methods:
static class CompanyEmployee
{
public static void DoSomething() { /*...*/ }
public static void DoSomethingElse() { /*...*/ }
}
A constant or type declaration is implicitly a static member.
A static member cannot be referenced through an instance. Instead, it is referenced through the type name. For example, consider the following class:
public class MyBaseC
{
public struct MyStruct
{
public static int x = 100;
}
}
To refer to the static member x, use the fully qualified name (unless it is accessible from the same scope):
Console.WriteLine(MyBaseC.MyStruct.x);
While an instance of a class contains a separate copy of all instance fields of the class, there is only one copy of each static field.
It is not possible to use this to reference static methods or property accessors.
If the static keyword is applied to a class, all the members of the class must be static.
Classes and static classes may have static constructors. Static constructors are called at some point between when the program starts and the class is instantiated.
Note
The static keyword has more limited uses than in C++. To compare with the C++ keyword, see Static (C+).
To demonstrate static members, consider a class that represents a company employee. Assume that the class contains a method to count employees and a field to store the number of employees. Both the method and the field do not belong to any instance employee. Instead they belong to the company class. Therefore, they should be declared as static members of the class.
This example reads the name and ID of a new employee, increments the employee counter by one, and displays the information for the new employee and the new number of employees. For simplicity, this program reads the current number of employees from the keyboard. In a real application, this information should be read from a file.
public class Employee4
{
public string id;
public string name;
public Employee4()
{
}
public Employee4(string name, string id)
{
this.name = name;
this.id = id;
}
public static int employeeCounter;
public static int AddEmployee()
{
return ++employeeCounter;
}
}
class MainClass : Employee4
{
static void Main()
{
Console.Write("Enter the employee's name: ");
string name = Console.ReadLine();
Console.Write("Enter the employee's ID: ");
string id = Console.ReadLine();
// Create and configure the employee object:
Employee4 e = new Employee4(name, id);
Console.Write("Enter the current number of employees: ");
string n = Console.ReadLine();
Employee4.employeeCounter = Int32.Parse(n);
Employee4.AddEmployee();
// Display the new information:
Console.WriteLine("Name: {0}", e.name);
Console.WriteLine("ID: {0}", e.id);
Console.WriteLine("New Number of Employees: {0}",
Employee4.employeeCounter);
}
}
/*
Input:
Matthias Berndt
AF643G
15
Sample Output:
Enter the employee's name: Matthias Berndt
Enter the employee's ID: AF643G
Enter the current number of employees: 15
Name: Matthias Berndt
ID: AF643G
New Number of Employees: 16
*/
This example shows that although you can initialize a static field by using another static field not yet declared, the results will be undefined until you explicitly assign a value to the static field.
class Test
{
static int x = y;
static int y = 5;
static void Main()
{
Console.WriteLine(Test.x);
Console.WriteLine(Test.y);
Test.x = 99;
Console.WriteLine(Test.x);
}
}
/*
Output:
0
5
99
*/
C# Language Specification
For more information, see the following sections in the C# Language Specification:
1.6.6.3 Static and instance methods
5.1.1 Static variables
10.3.7 Static and instance members
10.5.1 Static and instance fields
10.5.5.1 Static field initialization
10.6.2 Static and instance methods
10.7.1 Static and instance properties
10.8.3 Static and instance events
10.12 Static constructors
See Also
Concepts
Reference
Static Classes and Static Class Members (C# Programming Guide)
Other Resources
Change History
Date |
History |
Reason |
|---|---|---|
September 2008 |
Clarified and updated text. |
Customer feedback. |