You do not directly set the Node that is displayed by an Explorer view component (Swing components that display Nodes) by calling a method on that component. Rather, you set that kind of information by finding the manager for that component - it's what is in charge of what node is displayed, selected, etc.
The manager may be explicitly set on an Explorer view, but usually this is not necessary. When you add a view component (such as a BeanTreeView) to a Swing container, it will search backward through its parent, it's parent's parent, and so forth, looking for a component that implements ExplorerManager.Provider (an interface with one method - getExplorerManager()). That ExplorerManager is what will determine what is displayed.
While this may seem like an unnecessary layer of indirection, it is actually quite powerful: It makes it possible to very simply create master-detail views ala Windows Explorer: Just add two views to a JPanel subclass that implements ExplorerManager.Provider. It is very easy to set it up so changing the selection in one causes the other one to show the children of the selected object - just the way selecting a folder in Windows Explorer does.
See also the ExplorerManager javadoc.
Source: NetBeans FAQ