CalculateCorrectColumnWidths

// properly resize columns in a jtable.
// uses header renderers and cell renderers.
public void calculateCorrectColumnWidths() {
    JTableHeader header = table.getTableHeader();
    TableCellRenderer defaultHeaderRenderer = null;

    if (header != null) {
        defaultHeaderRenderer = header.getDefaultRenderer();
    }

    TableColumnModel columnModel = table.getColumnModel();
    TableModel tableModel = table.getModel();

    int margin = columnModel.getColumnMargin();

    for (int i = columnModel.getColumnCount() - 1; i >= 0; --i) {
        TableColumn column = columnModel.getColumn(i);

        int columnIndex = column.getModelIndex();

        int width = -1;

        TableCellRenderer cellRenderer = column.getHeaderRenderer();

        if (cellRenderer == null) {
            cellRenderer = defaultHeaderRenderer;
        }

        if (cellRenderer != null) {
            Component c = cellRenderer.getTableCellRendererComponent(
                    table,
                    column.getHeaderValue(),
                    false,
                    false,
                    -1,
                    i);

            width = c.getPreferredSize().width;
        }

        for (int row = tableModel.getRowCount() - 1; row >= 0; --row) {
            TableCellRenderer r = table.getCellRenderer(row, i);

            Component c = r.getTableCellRendererComponent(table,
                    tableModel.getValueAt(row, columnIndex),
                    false, false, row, i);

            width = Math.max(width, c.getPreferredSize().width);
        }

        if (width >= 0) {
            column.setPreferredWidth(width + margin);
        }
    }
}