Core Concepts: Classes and Objects

Example: Creating a Class and Object

Here's an example of a simple class and how to create objects from it in C#:

// Define a class
public class Car
{
    // Fields (data members)
    public string make;
    public string model;
    public int year;

    // Constructor
    public Car(string make, string model, int year)
    {
        this.make = make;
        this.model = model;
        this.year = year;
    }

    // Method
    public void DisplayInfo()
    {
        Console.WriteLine($"Car: {year} {make} {model}");
    }
}

// Create objects
Car car1 = new Car("Toyota", "Camry", 2022);
Car car2 = new Car("Honda", "Accord", 2023);

// Use objects
car1.DisplayInfo(); // Output: Car: 2022 Toyota Camry
car2.DisplayInfo(); // Output: Car: 2023 Honda Accord
            

In this example, Car is a class that defines the blueprint for cars, and car1 and car2 are objects created from this class.

Example: Constructor and Destructor

public class Book
{
    public string title;
    public string author;

    // Constructor
    public Book(string title, string author)
    {
        this.title = title;
        this.author = author;
        Console.WriteLine($"Book '{title}' by {author} is created.");
    }

    // Destructor (finalizer)
    ~Book()
    {
        Console.WriteLine($"Book '{title}' by {author} is destroyed.");
    }
}

// Create and use an object
Book book1 = new Book("The Great Gatsby", "F. Scott Fitzgerald");
// Output: Book 'The Great Gatsby' by F. Scott Fitzgerald is created.

// At the end of the program or when the object goes out of scope:
// Output: Book 'The Great Gatsby' by F. Scott Fitzgerald is destroyed.
            

In this example, the constructor initializes a Book object with a title and author, and the destructor cleans up resources when the object is no longer needed.

Example: Access Modifiers

public class Employee
{
    private string name; // Private field
    public int salary;   // Public field

    public Employee(string name, int salary)
    {
        this.name = name;
        this.salary = salary;
    }

    public void DisplayInfo()
    {
        Console.WriteLine($"Employee: {name}, Salary: {salary}");
    }
}

// Create and use an object
Employee emp1 = new Employee("John Doe", 50000);
emp1.DisplayInfo(); // Output: Employee: John Doe, Salary: 50000
            

In this example, name is a private field, accessible only within the Employee class, while salary is a public field accessible from outside the class.