C# - Static Members and Namespaces

Static Fields

A static field belongs to the class, not to any individual instance. All objects of the class share the same value. Access it via ClassName.FieldName.

csharp

class Person
{
    public static int Instances = 0;
    public string Name;

    public Person(string name)
    {
        Name = name;
        Instances++;
    }
}

new Person("Alice");
new Person("Bob");
Console.WriteLine(Person.Instances);

Output

Static Fields — Exercise 1

Static fields are accessed through the class name, not through an object reference.

Fix the static field access

Hint

Static members are accessed with ClassName.MemberName, not through an instance.

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

One per instanceZero — static fields are destroyed after creationOne shared copy for the entire classTwo — one for each thread

Static Methods

A static method belongs to the class. It can only access static members directly — it has no this reference. Utility methods like Math.Sqrt() are static.

csharp

class MathHelper
{
    public static int Square(int n) => n * n;
    public static bool IsEven(int n) => n % 2 == 0;
}

Console.WriteLine(MathHelper.Square(4));
Console.WriteLine(MathHelper.IsEven(7));

Output

16
False

Static Methods — Exercise 1

A static method cannot reference instance members because it has no object context.

Fix the instance member access inside a static method

Hint

A static method can only access static members. Make Prefix static.

Which statement about static methods is correct?

They can access instance fields directlyThey require an object to be calledThey are called on the class, not on an instanceThey are always private

Static Constructor

A static constructor (static ClassName()) runs once, automatically, before the first use of the class. It has no access modifier and no parameters. Use it to initialize static fields.

csharp

class Config
{
    public static string AppName;

    static Config()
    {
        AppName = "MyApp v1.0";
        Console.WriteLine("Static constructor called.");
    }
}

Console.WriteLine(Config.AppName);
Console.WriteLine(Config.AppName);

Output

Static constructor called.
MyApp v1.0
MyApp v1.0

How many times does a static constructor run?

Once per instanceOnce per program run, before first use of the classEvery time a static method is calledNever automatically

The this Keyword

this refers to the current instance. It is necessary when a parameter name shadows an instance field with the same name.

csharp

class Point
{
    private int x;
    private int y;

    public Point(int x, int y)
    {
        this.x = x;
        this.y = y;
    }

    public void Print() => Console.WriteLine($"({x}, {y})");
}

new Point(3, 7).Print();

Output

(3, 7)

The this Keyword — Exercise 1

Without this, writing name = name inside a constructor assigns the parameter to itself, leaving the field unchanged.

Fix the shadowed field assignment

Hint

Use this.name to distinguish the instance field from the parameter name.

What does this refer to inside an instance method?

The class definitionThe current object instanceThe parent classThe static version of the class

Namespaces

Namespaces organise related classes and prevent name collisions. using at the top of a file imports a namespace so you don't need the full qualified name.

csharp

using System;

namespace Geometry
{
    class Circle
    {
        public double Radius;
        public double Area() => Math.PI * Radius * Radius;
    }
}

Geometry.Circle c = new Geometry.Circle { Radius = 5 };
Console.WriteLine(Math.Round(c.Area(), 2));

Output

78.54

Namespaces — Exercise 1

Without the correct using directive, the compiler cannot find the type. Add the directive to resolve the error.

Add the missing using directive

Hint

Console lives in System. List<T> lives in System.Collections.Generic.

What is the purpose of a namespace?

To speed up compilationTo organise classes and avoid name collisionsTo declare global variablesTo define access modifiers

EX7 Practice — GalleryVisitor Statistics

From EX7: static constructor message, instance constructor increments total visitors, and static report method.

What should a static ShowStatistics method read to print total visitor count?

An instance fieldA local variableA static property like TotalVisitorsA constructor parameter

EX7 Practice — Product Counter

Product should track total created objects with a private static counter incremented in constructor.

Where should TotalProducts++ be placed to count every created product?

Inside discount()Inside static constructor onlyInside instance constructorInside Main after each new

EXXXX Trace — Counter Alias

Counter c3 = c1 creates an alias, not a new object.

After Counter c1 = new Counter(); Counter c2 = new Counter(); Counter c3 = c1;, what is Counter.Count?

1230

EXXXX Trace — Global vs Instance

GlobalCount is static and shared; InstanceCount belongs to each object separately.

If c1 increments twice and c2 increments once, what are (c1.InstanceCount, Counter.GlobalCount)?

(1,1)(2,2)(2,3)(3,3)

Bro Code Review — Static Access Rule

Static methods do not have this and should not directly touch instance fields.

Why can a static method not directly read instance field name?

Instance fields are always privateNo object context exists in static methodsThe compiler removes instance fieldsStatic methods run before classes load