Can you give an example of implementing the Chain of Responsibility pattern in programming code?

The Chain of Responsibility pattern allows passing a request along a chain of handlers until one of them handles the request.

Example in C#:

// Abstract handler
abstract class Handler
{
    protected Handler next;

    public void SetNext(Handler nextHandler) {
        next = nextHandler;
    }

    public virtual void Handle(string request) {
        if (next != null) {
            next.Handle(request);
        }
    }
}

// Concrete handlers
class ConcreteHandlerA : Handler
{
    public override void Handle(string request) {
        if (request == "A") {
            Console.WriteLine("Handled by ConcreteHandlerA");
        } else {
            base.Handle(request);
        }
    }
}

class ConcreteHandlerB : Handler
{
    public override void Handle(string request) {
        if (request == "B") {
            Console.WriteLine("Handled by ConcreteHandlerB");
        } else {
            base.Handle(request);
        }
    }
}

// Usage
var handlerA = new ConcreteHandlerA();
var handlerB = new ConcreteHandlerB();
handlerA.SetNext(handlerB);

handlerA.Handle("B"); // Will output: Handled by ConcreteHandlerB

In this example, the request is passed along the chain of handlers until a suitable one is found.