The Chain of Responsibility pattern promotes loose coupling by removing the sender's knowledge of exactly which object will handle its request. The sender only knows about the first handler in the chain; every handler after that is discovered dynamically as the request moves along.
Key Points: • The client sends a request to the chain's entry point without knowing which handler will ultimately process it. • Each handler only needs a reference to the next handler, not to every other handler or to the sender. • Handlers can be added, removed, or reordered without changing the sending code at all. • Individual handlers can be developed and tested independently, since they only implement a shared handler interface. • The pattern separates "who initiates a request" from "who satisfies it," which keeps both sides free to evolve independently.
Example: An HTTP request filter chain (authentication, logging, rate limiting) lets each filter decide whether to process the request or pass it along, and new filters can be inserted without modifying the controller that originally received the request.
Interview Tip: A concise interview answer is:
"The sender only ever talks to the first handler in the chain, not to whichever handler eventually processes the request, so the two are decoupled. Because each handler just knows about the next one, I can add, remove, or reorder handlers freely without touching the client code that kicked off the request."