What are the advantages and disadvantages of using interfaces in programming?

Advantages of using interfaces:

• They allow defining a contract that classes must implement, providing flexibility and extensibility.
• They support multiple inheritance of types, which classes do not.
• They ensure loose coupling between components, making testing and maintenance easier.
• They enable polymorphism — objects of different classes can be used through a common interface.

Disadvantages:

• Interfaces do not contain implementation (until default methods appeared), which can lead to code duplication.
• Changing an interface (e.g., adding new methods) can break existing implementations if default methods are not used.
• Design complexity: too many interfaces can complicate architecture.

Example:

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

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

Here, the ILogger interface defines a contract for logging, and the ConsoleLogger class implements it, allowing easy swapping of logger implementations without changing the code that uses it.