Constructors

Syntax

public ClassName(parameters) {\n  // initialization code\n}

Examples

public class Point
{
    public int X, Y;

    public Point(int x, int y)
    {
        X = x;
        Y = y;
    }
}

Point p = new Point(3, 4);
Console.WriteLine($"({p.X}, {p.Y})");  // (3, 4)

public class Rectangle
{
    public double Width, Height;

    public Rectangle()
    {
        Width = 1;
        Height = 1;
    }

    public Rectangle(double side)  // square shortcut
    {
        Width = side;
        Height = side;
    }

    public Rectangle(double width, double height)
    {
        Width = width;
        Height = height;
    }
}

Rectangle r1 = new Rectangle();       // 1x1
Rectangle r2 = new Rectangle(5);       // 5x5 square
Rectangle r3 = new Rectangle(4, 6);    // 4x6

public class User
{
    public string Name;
    public string Role;

    public User(string name) : this(name, "member")
    {
    }

    public User(string name, string role)
    {
        Name = name;
        Role = role;
    }
}

User u1 = new User("Fola");           // Fola (member)
User u2 = new User("Zain", "admin");   // Zain (admin)

public class Point(int x, int y)
{
    public int X { get; } = x;
    public int Y { get; } = y;

    public double DistanceFromOrigin() => Math.Sqrt(X * X + Y * Y);
}

Point p = new Point(3, 4);
Console.WriteLine(p.DistanceFromOrigin());  // 5

Best practices

• Use : this(...) to chain constructors and avoid duplicating initialization logic across multiple overloads
• Validate arguments inside constructors (throwing an exception for invalid values) to prevent objects from ever existing in an invalid state
• Keep constructors focused on initialization - avoid putting complex business logic or I/O operations inside them
• Consider primary constructors (C# 12+) for simple classes where the constructor parameters map directly onto properties

At a glance

Purpose

Applications on the .NET platform

File extension

.cs

Runs in

.NET runtime

Usually used with

.NET SDK and libraries

Specifications & further reading

• C# language reference

Related C# documentation