As more and more people are diving into Eclipse in the Notes community one very important area of the Eclipse workbench that needs to be understood is the Eclipse Workbench Selection and then more importantly Adapters. Understanding these two basic concepts will let your Eclipse view (or component) interact with other Eclipse parts with no “wiring”. The workbench selection is a fixed pub/sub where your component will be notified any time another part changes its selection – a workbench window only has one selection at a time. This allows your view part to show relative information to the new selection. The Adapter pattern explained in the linked article explains how you can provide selection objects that can be adapted to other well known object types. It also shows you how you can adapt an existing selectable object type to something else.
Many of the side bar components that work off of a currently selected email or document use this pattern. This allows your side bar component to be able to respond to what is currently selected.
Adapters article on Eclipse.org.