Accessing the "Class Hierarchy" view is not easy:
In Eclipse, pressing F4 on the class name is all that is needed. Should be just as simple in NetBeans.
Note that in IDEA, the user also needs >= 2 keystrokes: CTRL-H to open the hierarchy view, then select supertype/subtype hierarchy as needed. Shortcuts for changing the hierarchy are even not assigned by default (actions are available for assignment though).
I believe for short task, a workaround CTRL-ALT-B (Go To implementation) is enough. For hierarchy inspection or browsing (not so often task), 2 keystrokes are acceptable.