My experience with NetBeans is that the generated code when building GUIs in particular is extremely difficult to read and subsequently maintain.
That depends on the layout that is selected for the container. I don't find the generated code more difficult to read than any other complex layout code. GridBagLayout, GroupLayout, and SpringLayout do involve quite a bit of code and the GUI builder does save a lot time over manually coding it. That said, I agree it is still a good idea for beginners to learn to code it for themselves so they understand the nuances of those layouts.