The column width can be set via ColumnDefinition, e.g.,

dataBook.getRowDefinition().getColumnDefinition("FUNCTION").setWidth(231);

The table uses this width for the cell width.

But be careful, the real cell width depends on the UI implementation. Some GUI toolkits like Swing fill the empty space and add the difference to existing cells. In the case of Swing UI, it's possible to disable this feature:

(((JVxTable)table.getResource()).setAutoFillEmptySpace(false);