I am still in my first few months of programming so please bear with me if the problems are stupid-easy to fix.
When I changed the the Books file to an Abstract class, it created a few compatibility issues. I fixed most, but there are still a couple of errors that I can't wrap my head around.
Also, when I list the books, it doesn't show in the GUI, and also errors should show in a JOptionPane I guess, not sure. :/
Help would be greatly appreciated! Hope to have a positive first experience on this website