The Hierarchy tool window is not shown when there are no hierarchies to display. You have to build hierarchies first.
Refer to Building Class Hierarchy to learn how to build hierarchies.
- On the main menu, choose .
- Use Alt+8Alt+8 keyboard shortcut.
- Right-click the currently displayed tab, and choose / on the context menu.
- Use the Alt+RightAlt+Right and Alt+LeftAlt+Left keyboard shortcuts.
- Click the currently displayed tab, and choose the next tab to display.