C# static keyword

In this tutorial, we would learn about static keyword in c# programming language.

static : something which belongs to the type itself, not with an instance of the type.

The modifier in C# language applies to the following :

1. Variable

2. Methods

3. Class

4. Constructor

Now we would look at examples of each

static variable

• static variables are accessed with the name of the class.

• Only a single copy of the variable is created and shared among all the instances of the class.

• static variable can't be accessed with the instance.

• var can not be used to declare a static variable, one must specify the type of variable after the static keyword.

   public class Employee{
        public static int EmpCount = 0;
        public void AddEmployee(){
            EmpCount++;
        }
    }
    public static void Main(string[] args){
        Console.WriteLine("Start Of the Program");
        Employee emp1 = new Employee();
        emp1.AddEmployee();
        Console.WriteLine(Employee.EmpCount); // output 1

        Employee emp2 = new Employee();
        emp2.AddEmployee();
        Console.WriteLine(Employee.EmpCount); // output 2
        Console.WriteLine(emp2.EmpCount); // compilation error
        Console.ReadKey();
    }

static method

• Similar to static variables, static methods are also accessed with the name of the class.

• static methods could use both static and non-static class members.

• static members are directly accessed inside the static method without a class name, and non-static members are accessed using instances.

        public class Employee {
        private string FirstName;
        private string LastName;
        public Employee(string firstName, string lastName) {
            FirstName = firstName;
            LastName = lastName;
        }
        public string FullName { 
                get{
                    return ($"{this.FirstName} {this.LastName}");
                } 
        }
        public static int EmpCount = 0;
        public static void AddEmployee(Employee emp) {
            EmpCount++;
            Console.WriteLine(emp.FullName);
        }
    }
    public static void Main(string[] args) {
        Console.WriteLine("Start Of the Program");
        Employee emp1 = new Employee("John", "Smith");
        Employee.AddEmployee(emp1); // "John Smith" : instance specific data
        Console.WriteLine(Employee.EmpCount); // 1: static data
        Employee emp2 = new Employee("John", "Bold"); // "John Bold" : instance specific data
        Employee.AddEmployee(emp2);
        Console.WriteLine(Employee.EmpCount); // 2: static data
        Console.ReadKey();
    }

static constructor

• a static constructor is used to initialize static data or to perform an action that needs to be performed only once.

• A class can have only one static constructor.

• No parameter, No access modifier, No inheritance or overloading

• static methods could use both static and non-static class members.

• a static constructor is called automatically by the CLR. The user has no control over when a static constructor is executed in the program. static constructor runs before the instance constructor.

• a static constructor is called only for a single time during program execution.

    public class Organization {        
        static Organization() {
            Console.WriteLine("Static constrctor called");
        } 
        public Organization() {
            Console.WriteLine("Instance constructor called");
        }
    }
    public static void Main(string[] args) {
        Console.WriteLine("Start Of the Program");        
        Organization org1 = new Organization();
        Console.ReadKey();
    }
** Output **
Start Of the Program
Static constrctor called
Instance constructor called

static class

• static class can only contain static data members, static methods and static constructor. [Error if there are non-static fields, the non-static method in static class]

• Instances can not be created for a static class. [Error if user tries to create an instance of static class]

• static classes are sealed, they can't be inherited.

• static members can be accessed directly without using the class name inside the static class.

    public static class Organization {
        private static string FounderName = "James Clark";
        private static DateTime StartDate = new DateTime(1990, 01, 01);

        public static string Introduction;
        static Organization() {
            Introduction = $"This organization was founded by {FounderName} in {StartDate.Year}";
        }
    }
    public static void Main(string[] args) {
        Console.WriteLine("Start Of the Program");
        Console.WriteLine(Organization.Introduction);
    }
** Output **
Start Of the Program
This organization was founded by James Clark in 1990.

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In this post, we have learned about static keyword in c#. Please share your feedback and suggestios to improve this.