JScrollPane : Java Glossary

Tips

• Add the contents to be scrolled in the JScrollPane constructor. Don’t add it later the way you do with ScrollPane. For some reason, if you add it later, all you see then is a blank panel, even though all the code appears to paint normally. You can however add/change it later with setViewportView.
• You can freeze a non-vertically-scrolling header with setColumnHeader or setColumnHeaderView just like a spreadsheet. There are analogous features for non-horizontally-scrolling row headers.
• You can control what is visible with by getting the horizontal or vertical JScrollBar and using setValue.
• JScrollPane lets you independently control whether there are vertical or horizontal scroll bars, unlike AWT ScrollPane which requires both to be set the same way.

Making Visible

// make part of a JTable visible in the scroll region.
// Must run on Swing thread.
final Rectangle r = jTable.getCellRect( rowIndex, colIndex, true );
if ( r != null )
   {
   jTable.scrollRectToVisible( r );
   }

Gotchas

• There is a setViewPosition method defined for JScrollPane, JComponent (of the component being scrolled) and Viewport. Each behaves slightly differently.
• To scroll back to the top, JscrollPane.getVerticalScrollBar.setValue does nothing. You must use TextComponent.setCaretPosition instead or JTable.scrollRectToVisible.

Learning More

Fighting over the Scroller

Any program that uses JScrollPane has a potential problem if it ever sets the position of the scroll using one of the techniques above. The user may also be trying to scroll at the same time. The program should defer to the user, e.g. if the user has recently moved the scroll, or is holding the thumb bar with mouse right now, defer the scroll move to later and ignore it entirely if there is another scroll setting. This logic properly belongs in JScrollPane. I wonder if anyone has ever tackled this problem or wants to. There might even be a way to introduce and enhanced JScrollPane into arbitrary programs unaware of the problem, with a L&F.