When an event is raised by an object (publisher), it sends out a signal that other objects (subscribers) can receive. The signal is in the form of a notification that can indicate the occurrence of an action. In an event system, an object broadcasts an event. Only those objects that subscribe to it will be notified and choose how to handle it. So, we can imagine it as having a sudden burst of a radio signal that only those with antennas tuned to a specific frequency can detect.

The Event Bus pattern is a close cousin of the Messaging system and Publish-Subscribe patterns, the latter being the more accurate name for what the Event Bus does. The keyword in the title of this pattern is the term bus. In simple computing terms, a bus is a connection between components. In the context of this chapter, the components will be objects that can be publishers or listeners of events.

Hence, the Event Bus is a way to connect objects through events by using a publish...