Right, let me re-phrase this. Since my purpose is to add a row to my Table I
need to create an addRow method such as:

************************************************
class MyTableModel extends AbstractTableModel {

   String[] columnNames = {"Nom. dia.","Dia. (in)",
                                       "Instal. Cost",
                                       };

             ArrayList  data = new  ArrayList();

       public void addRow(Object row) {
         data.add(row);
         fireTableDataChanged();
       }
       public int getColumnCount() {
           return columnNames.length;
       }

       public int getRowCount() {
           return data.size()/3;
       }

       public String getColumnName(int col) {
           return columnNames[col];
       }

       public Object getValueAt(int row, int col) {
                  return (String[])data.get(row))[col];
       }

               public Class getColumnClass(int c) {
           return getValueAt(0, c).getClass();
       }

           public boolean isCellEditable(int row, int col) {
                          return true;
                }

             public void setValueAt(Object value, int row, int col) {

           data[row][col] = (String[])data.set(row, Value))[col];
                     fireTableCellUpdated(row, col);

           }
       }

           }
********************************************

The getValue and setValue follow your recommendations but they do not work,
compiler halts at the getValue method and says "expecting ";"......"

Jacques

You need context to analyse compiler messages.  The error is often in
a declaration or some nearby code.