Constructors and Destructors in C#

# CHAPTER 14

Constructors and Destructors #

1. Introduction #

2. Learning Objectives #

• Define a Constructor.

• Create Parameterized Constructors.

• Overload Constructors.

• Understand the this keyword.

• Understand Destructors and Garbage Collection.

3. What is a Constructor? #

• It MUST have the exact same name as the class.

• It has no return type (not even void).

class Player
{
    public int health;

    // Default Constructor
    public Player()
    {
        health = 100; // Every player starts with 100 health automatically!
        Console.WriteLine("Player created!");
    }
}

class Program
{
    static void Main()
    {
        Player p1 = new Player(); // "Player created!" is printed instantly.
        Console.WriteLine(p1.health); // Prints 100
    }
}

4. Parameterized Constructors #

class Car
{
    public string model;
    public int year;

    // Parameterized Constructor
    public Car(string m, int y)
    {
        model = m;
        year = y;
    }
}

class Program
{
    static void Main()
    {
        // We MUST provide the arguments now
        Car myCar = new Car("Mustang", 2024); 
    }
}

5. The this Keyword #

class User
{
    public string name;

    public User(string name)
    {
        // name = name; // Confusing! Which is the parameter, which is the field?
        
        this.name = name; // Correct! "This object's name = the parameter name"
    }
}

6. Constructor Overloading #

class Product
{
    public string Name;
    public decimal Price;

    // Constructor 1: Free product
    public Product(string name)
    {
        this.Name = name;
        this.Price = 0.0m;
    }

    // Constructor 2: Priced product
    public Product(string name, decimal price)
    {
        this.Name = name;
        this.Price = price;
    }
}

7. Destructors (Finalizers) #

Note: In modern C#, you rarely need to write destructors because the Garbage Collector handles memory perfectly. You only use them if you are dealing with unmanaged resources (like direct file handles or network streams).

class Connection
{
    public Connection()
    {
        Console.WriteLine("Connection Opened");
    }

    // Destructor
    ~Connection()
    {
        Console.WriteLine("Connection Closed by Garbage Collector");
    }
}

8. OOP and Memory Explanation #

9. Common Mistakes #

• Putting a return type on a constructor: If you write public void Player(), the compiler thinks it is a normal method, NOT a constructor. It will not be called automatically.

• Relying on Destructors for timing: You cannot predict exactly *when* the Garbage Collector will run. Therefore, you don't know exactly when the destructor will execute. For immediate cleanup, C# uses the IDisposable interface instead.

10. Best Practices #

• Use constructors to force the caller to provide required data. If a Bank account absolutely requires an ID, make the constructor require an ID, making it impossible to create an invalid blank account.

11. Exercises #

1. 1. Create a Book class with a constructor that requires a title and pages. Use the this keyword.

1. 2. Add a second overloaded constructor that only takes title and defaults the pages to 100.

12. MCQs with Answers #

Q9. Is it necessary to manually write a destructor to free normal memory in C#? a) Yes b) No, the Garbage Collector handles it automatically Answer: b) No, the Garbage Collector handles it automatically

13. Interview Questions #

• Q: Explain the purpose of the this keyword.

• Q: What is the difference between a Constructor and a Destructor?

• Q: Why might you make a constructor private? (Answer: To prevent external classes from creating objects, commonly used in the Singleton design pattern).

14. Summary #

15. Next Chapter Recommendation #