Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. Chain the receiving objects and pass the request along the chain until an object handles it.

Source code

/**  * Handles request it is responsible to.  */ public class ConcreteHandler extends Handler {         /**   * Handle request or delegate it.   */         public void handleRequest() {                 boolean canProcessThisRequest = false;                if (canProcessThisRequest) {                         // handle request if possible                 } else {                         // pass it to the next in chain                         super.handleRequest();                }         }  }  /**  * Defines interface for request handling  * @role __Handler  */ public class Handler {         private Handler successor;        /** Default request handling */         public void handleRequest() {                 if (successor != null) {                         successor.handleRequest();                }         }          public Handler getSuccessor() {                 return this.successor;        }          public void setSuccessor(Handler successor) {                 this.successor = successor;        }  }