| Delegates | Notifications |
|---|---|
| One-to-one communication | One-to-many or many-to-many communication |
| Customized behavior | Broadcasting information/events |
| Delegate object holds a reference | Observing objects don’t need references |
| Specific responsibilities/tasks | Widely distributed information/events |
| Tight coupling between objects | Loose coupling between objects |
| Object needs to know its delegate | Posting object doesn’t know receivers |
| Callbacks, data source protocols, event handling | Application-wide event handling |
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