Java SE (Java Platform, Standard Edition)

I have a JTable inside JScrollPane that has fixed number of rows. I have a function that calculates the preferred width of the table (taking into account the max width of every column for all the rows) so all the column�s text is visible.

JTable tagTable = new JTable(modulesValueTableModel);
JScrollPane scrollPane = new JScrollPane();
scrollPane.setViewportView(tagTable);
initColumnSizes(scrollPane, tagTable, modulesValueTableModel);

What I want is to set the viewport of the JScrollPane so it shows only table with all actual rows (no empty space at the bottom).
If I don�t re-adjust the height of the scrollPane I get the empty space at the bottom of the scrollPane.
When I set the viewport size to the preferred size of the table (as below) it truncates a little bit one column�s width (just few pixels) as if the preferred width of the tagTable was a little bit too small for the viewport:
scrollPane.getViewport().setPreferredSize(
new Dimension(tagTable.getPreferredSize().width,
tagTable.getPreferredSize().height));
When I set the viewport like below (using width of the scrollPane) it works as I want it to:
scrollPane.getViewport().setPreferredSize(
new Dimension(scrollPane.getViewport().getPreferredSize().width,
tagTable.getPreferredSize().height));
What am I missing here � it looks to me that the tagTable.getPreferredSize().width value is little bit smaller then the viewport needs to be so it hides a bit of one column.
Any help appreciated.
Janusz