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event-aggregator/README.md

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+---
+layout: pattern
+title: Event Aggregator
+folder: event-aggregator
+permalink: /patterns/event-aggregator/
+categories: Structural
+tags:
+ - Java
+ - Difficulty-Beginner
+---
+
+## Intent
+A system with lots of objects can lead to complexities when a
+client wants to subscribe to events. The client has to find and register for
+each object individually, if each object has multiple events then each event
+requires a separate subscription. An Event Aggregator acts as a single source
+of events for many objects. It registers for all the events of the many objects
+allowing clients to register with just the aggregator.
+
+![alt text](./etc/classes.png "Event Aggregator")
+
+## Applicability
+Use the Event Aggregator pattern when
+
+* Event Aggregator is a good choice when you have lots of objects that are
+  potential event sources. Rather than have the observer deal with registering
+  with them all, you can centralize the registration logic to the Event
+  Aggregator. As well as simplifying registration, a Event Aggregator also
+  simplifies the memory management issues in using observers.
+
+## Credits
+
+* [Martin Fowler - Event Aggregator](http://martinfowler.com/eaaDev/EventAggregator.html)