The Change Facet of an object (Figure 4.3) publishes the change Bean event set and fires an event whenever the primary object has changed in a manner that will affect observers.

Figure 4.3. The Change Facet.

Other objects (including other Facets of the primary object) may utilize the Change Facet as a way to isolate themselves from the details whereby an object indicates a state change.

The Change interface is designed to accommodate -- and shield other components from the distinctions between -- cases where the primary object informs clients of changes to itself and cases where the end-user must manually trigger an "update" of all views. The Change.automaticallyUpdating property indicates whether the associated Change Facet is listening for events from its primary object. If this property is true, then calls to its Change.fireChange() method should be no-ops. However, if this property is false, each call to Change.fireChange() will force the broadcast of a ChangeEvent.