I subscribe to newspapers/TvChannels Newspapers/TVchannels subscribe to celebriities. So we know of events. Whenever I want time I check my watch but when I am sleeping, I subscribe to an alarm. Best possible I pull info but (if it is inefficient for an event ) I prefer to be informed. In general observer pattern is story of a passive observer that dont want to observe. "Let me know if it changes" attitude. oh sorry, If too many components need to observe samething? Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.

So as I told earlier, A lazy observer subscribes. Publishers will inform the subscribers when something changes. So the publisher will have a list of subscribers in a list. Whenever the publishers property changes...he will inform all subscribers class Publisher { ArrayList mysubscribers; public MyProperty { get {return myProp;} set { myProp = value; foreach (subscriber s in mysubscribers) { inform(s); } } } } More than software engineering, this pattern is very well used in real life. In software Engineering, this is a most used pattern. 1) Even triggers in DB are meant for same purpose. 2) "SQL notification services" is a product to demonstrate the need of this pattern. 3) Do you use gadgets/browse webpages/ subscribe to RSS feeds? -- This is not observer pattern. If you subscribe to an event to get an email, that is observer pattern.