problem displaying jtable

[kobe phenom]

At first my JTable is displaying fine (data is retrieving from
database). I have created a data model that derived from
AbstractTableModel and using that data model for my JTable.
But in time when any data changes, I have to update my JTable in display.
Problem is that although JTable is displaying, the JTable no longer
spans all of the available space, I have to manually resize all columns to fit into available spaces.
Can anyone help me?Thanks in advance.