Static Members

Static Members

What it means

A static member belongs to the class itself, not to any individual instance — there’s only ever one copy, shared across every use, and you access it through the class name rather than an object reference. Common uses: utility methods that don’t need instance state (Math.Sqrt), shared counters, and constants.

Examples

public class Counter
{
    public static int TotalCount;   // shared across ALL instances

    public Counter()
    {
        TotalCount++;                // every new Counter increments the SAME shared field
    }
}

var c1 = new Counter();
var c2 = new Counter();
var c3 = new Counter();
Console.WriteLine(Counter.TotalCount);   // 3 -- accessed via the class name, not an instance

public static class MathHelpers   // an entire static class -- can't be instantiated
{
    public static double CelsiusToFahrenheit(double c) => c * 9 / 5 + 32;
}

double f = MathHelpers.CelsiusToFahrenheit(20);   // no `new` needed

Common mistake

Trying to access an instance member from a static method (or vice versa, expecting a static field’s value to differ per instance) — static methods have no this and can’t see instance data, since they aren’t tied to any particular object.

public class Person
{
    public string Name;

    public static void Greet()
    {
        Console.WriteLine($"Hello, {Name}!");   // Error: an object reference is required for the non-static field 'Name'
    }
}

// Fix: either make the method non-static, or pass the data in explicitly
public static void Greet(string name)
{
    Console.WriteLine($"Hello, {name}!");
}

Quick practice

1. How many copies of a static field exist across all instances of a class?

   Answer

   Exactly one, shared by every instance (and accessible even with zero instances created).

2. Can a static method access an instance field directly?

   Answer

   No — static methods have no this reference and aren't tied to any particular instance, so they can't see instance-level data without it being passed in explicitly.

3. What does a static class (like MathHelpers) prevent you from doing?

   Answer

   Creating instances of it with new — a static class can only contain static members and exists purely as a namespace-like container for related utility functionality.