Interface HierarchyListener notifies interested parties of changes in a hierarchically organized graph. The information is conveyed using objects of type HierarchyEvent, and covers changes that relate to hierarchy level modifications of graph elements.

To receive notifications, HierarchyListener implementations have to be properly registered with a HierarchyManager object. Figure 7.8, “Context for using HierarchyListener” gives an overview on interface HierarchyListener's role.

Class DefaultNodeChangePropagator can additionally be registered with the root graph of a hierarchically organized graph to notify interested parties of node label changes.