Class, Object, & Constructors

1. Description

A class is a blueprint for creating objects. It defines a set of properties (data) and methods (behaviors) that objects of that type will have. An object is an instance of a class, a concrete entity created from the blueprint. A constructor is a special method in a class that is called when a new object is created, used to initialize the object's properties.

2. Why It Is Important

Classes and objects are the fundamental concepts of Object-Oriented Programming (OOP). They allow you to model real-world entities, organize your code into logical units, and create reusable and maintainable code. Constructors ensure that objects are created in a valid and predictable state.

3. Real-World Examples

• A Car class can define properties like Color, Model, and Speed, and methods like Accelerate() and Brake(). Each individual car is an object of the Car class.
• A User class in a social media application could have properties like Username, Email, and a list of Posts.
• When creating a new User object, a constructor would ensure that the Username and Email are provided and are not empty.

4. Syntax & Explanation

using System;

// Defining a class named 'Customer'
class Customer
{
    // Properties
    public string Name { get; }
    public int Age { get; set; }

    // Constructor
    public Customer(string name, int age)
    {
        // Basic validation in the constructor
        if (string.IsNullOrWhiteSpace(name))
        {
            // Throw an exception if the name is not valid
            throw new ArgumentException("Name cannot be empty", nameof(name));
        }

        Name = name;
        Age = age;
    }

    // Method
    public void Print()
    {
        Console.WriteLine($"Customer: {Name}, Age: {Age}");
    }
}

class Program
{
    static void Main()
    {
        // Creating an object of the Customer class
        var customer1 = new Customer("Sam", 30);
        customer1.Print(); // Output: Customer: Sam, Age: 30

        // Creating another object
        var customer2 = new Customer("Alice", 25);
        customer2.Age = 26; // Modifying a property
        customer2.Print(); // Output: Customer: Alice, Age: 26
    }
}

5. Use Cases

• Modeling real-world entities in your application, such as Product, Order, Employee, etc.
• Encapsulating data and behavior into a single unit.
• Creating complex data structures.
• Ensuring that objects are always created in a valid state using constructors.

6. Mini Practice Task

1. Create a Product class with properties for Name (string) and Price (decimal).
2. Add a constructor to the Product class that accepts the name and price as parameters and initializes the properties.
3. In the constructor, add a validation to ensure that the Price is not negative. If it is, throw an ArgumentException.
4. Create a few instances of the Product class and print their details to the console.