How is the request to the interface made?

A request to an interface is made by calling methods or accessing properties of an instance of a class that implements this interface. You cannot create an instance of the interface itself.

Example:

// Interface declaration
public interface ILogger
{
    void LogMessage(string message);
}

// Class implementing the interface
public class ConsoleLogger : ILogger
{
    public void LogMessage(string message)
    {
        Console.WriteLine(message);
    }
}

// Using the interface
public class Application
{
    private readonly ILogger _logger;

    public Application(ILogger logger) // Dependency on the interface
    {
        _logger = logger;
    }

    public void Run()
    {
        _logger.LogMessage("Application started."); // Calling method via interface
    }
}

// Entry point
public class Program
{
    public static void Main(string[] args)
    {
        ILogger logger = new ConsoleLogger(); // Creating an instance of a class that implements the interface
        Application app = new Application(logger);
        app.Run();
    }
}

Main principles:

• Polymorphism: Allows referring to different implementations of an interface through a single data type (the interface).
• Abstraction: Hides implementation details and works only with the contract defined by the interface.
• Using an instance: A request to an interface always occurs through an instance of a class that implements the methods and properties declared in the interface.