In which cases is it recommended to use interfaces in software development?

Interfaces in C# are recommended to be used in the following cases:

• To define a contract that various classes must implement, ensuring polymorphism.
• When it is necessary to separate behavior definition from specific implementation.
• To simplify testing through dependency injection.
• When designing extendable and maintainable systems where implementations may change.
• To implement multiple different behaviors within a single class through multiple interface implementations.

Example of an interface and its implementation:

public interface ILogger
{
    void Log(string message);
}

public class ConsoleLogger : ILogger
{
    public void Log(string message)
    {
        Console.WriteLine(message);
    }
}

Using interfaces increases the flexibility and modularity of the code.