Lesson 13 — Object Initialisation

Constructors

C# constructors initialise objects. Constructor chaining with this(), base(), primary constructors (C# 12), and records reduce boilerplate.

CSHARP — Constructor chaining 
public class Learner {
    public string Name   { get; }
    public int    Age    { get; }
    public string Course { get; }
    public double Mark   { get; private set; }

    // Full constructor:
    public Learner(string name, int age, string course, double mark) {
        Name   = name;
        Age    = age;
        Course = course;
        Mark   = mark;
    }

    // Overload — delegates to full constructor:
    public Learner(string name, int age, string course)
        : this(name, age, course, 0.0) { }

    // Minimal constructor:
    public Learner(string name) : this(name, 0, "Undecided") { }

    public void Introduce() =>
        Console.WriteLine($"I am {Name}, studying {Course}. Mark: {Mark}%");
}

var l1 = new Learner("Thandi", 21, "C#", 74.5);
var l2 = new Learner("Sipho",  24, "Java");
var l3 = new Learner("Lerato");
l1.Introduce(); l2.Introduce(); l3.Introduce();

Primary Constructors (C# 12)

CSHARP — Primary constructors 
// Primary constructor — parameters available throughout the class body:
public class Learner(string name, int age, string course) {
    public string Name   => name;
    public int    Age    => age;
    public string Course => course;

    public void Introduce() =>
        Console.WriteLine($"I am {name}, aged {age}, studying {course}.");
}

// Records are even more concise:
record LearnerRecord(string Name, int Age, string Course, double Mark);

var r = new LearnerRecord("Bongani", 22, "SQL", 88.5);
Console.WriteLine(r); // LearnerRecord { Name = Bongani, ... }

Static Constructors

CSHARP — Static constructor 
public class Database {
    public static readonly string ConnectionString;

    // Static constructor — runs once when the class is first used:
    static Database() {
        ConnectionString = Environment.GetEnvironmentVariable("DB_CONN")
            ?? "Server=localhost;Database=your-it-tutor;";
        Console.WriteLine("Database class initialised.");
    }
}

Practice Task

Your Turn

Write a BankAccount class with: a full constructor taking accountNumber (final/readonly), holderName, and initialBalance; an overload taking only holderName and generating an accountNumber using a static counter; validation in the full constructor (balance >= 0). Show constructor chaining with : this().

Common Mistakes

  • Adding a return type to a constructor — makes it a regular method.
  • Not using this() delegation — copy-pasted constructor code breaks the DRY principle.
  • this() must be the first thing called — no code before it.
  • Records are immutable by default — use with to create modified copies.

Professional Tip

Constructor chaining keeps all initialisation logic in one place. The minimal constructors delegate to the full one — no duplicated validation code.

Mini Quiz

What does : this(...) do in a C# constructor?