Using the Java Debugger in NetBeans is not as easy as it looks. Here is a demo with a four class program that uses inheritance.
If your knowledge of Java inheritance is not good perhaps you should watch this presentation first. It also demonstrates the debugger but gives more background on inheritance at the same time. Then you should watch the presentation above for more detail on the debugging tool in NetBeans.
Debugging shortcuts
Ctrl-F5. Start debugging main project
Ctrl-Shift-F5. Start debugging current file
Ctrl-Shift-F6. Start debugging test for file
Shift-F5/F5. Stop/continue debugging session
F4. Run to cursor location in file
F7/F8. Step into/over
Ctrl-F7. Step out
Ctrl-Alt-Up. Go to called method
Ctrl-Alt-Down. Go to calling method
Ctrl-F9. Evaluate expression
Ctrl-F8. Toggle breakpoint
Ctrl-Shift-F8. New breakpoint
Ctrl-Shift-F7. New watch