JSplitPane : Java Glossary
Allows you to display exactly two Components, most often
two JPanels or two JScrollPanes, splitting the screen real estate in two either
vertically or horizontally. The user can adjust the split by dragging the divider.
Oddly JSPlitPane is not a subclass of JPanel. Here is how you use it:
You can programmatically control the position of the split with setResizeWeight or setDividerLocation.
Oracle’s tutorial explains the details.
Oracle’s Javadoc on JSplitPane
class : available: