I decided to write something about splitting NetBeans
editor windows, because it's one of those hidden features users keep asking for. The use case is that you want to edit the same file in two editor windows. Or you want to open two different files and compare them in split view. Many editors support this functionality and it is in NetBeans, too, although it is not commonly known.
To open one file in two windows, use Window->Clone document. Then you have the same file opened twice. To split the screen, just drag one window title to the bottom, till you get a rectangle on bottom of the editor. Drop it and you have splitted editing screen. Here is a screenshot:
Horizontal split - click for detail
Vertical split - click for detail