Question

Lets say that I have a message queue which receives messages which have the members name, type and so on.

Is there a name for a type of observer on this queue which expects a message with a certain content?

if (message.name.equals(observer.wantedName) {
  observer.notify();
}

Answer 1

The following is just an example in pseudo code how to solve the problem. The MessageQueue has a hashtable which keys are the message types and values arrays with listeners for this message type. Also you’ll need an additional argument to YourMessageQueue:observe() that describes the condition.

class YourMessageQueue extends /* or implements */ EventDispatcher {

    function addMsg(msg) {
        foreach(this.listeners[msg.type] as listener) {
            listener.notify(msg, this);
        }
    }
}


class YourObserver implements Observer {

    function createMesssageQueue() {
        msgq = new MessageQueue();
        msgq.addObserver(this, 'foo');
    }
}


class EventDispatcher {

    protected hashtable observers;

    function addObserver(Observer observer, string eventType) {
        this.observers[eventType].push(observer);
    }
}


interface Observer {

    function notify($data, $sender);
}