code: public void setValueAt(Object value, int row, int col) {
          if (log.isLoggable(Level.FINE)) {
              log.fine(
                  "Setting value at " + row + "," + col + " to " + value + " (an instance of " + value.getClass() + ")");
          }
  
          if (data[0][col] instanceof Integer && !(value instanceof Integer)) {
              //With JFC/Swing 1.1 and JDK 1.2, we need to create    
              //an Integer from the value; otherwise, the column     
              //switches to contain Strings.  Starting with v 1.3,   
              //the table automatically converts value to an Integer,
              //so you only need the code in the 'else' part of this 
              //'if' block.                                          
              //XXX: See TableEditDemo.java for a better solution!!!
              try {
                  data[row][col] = Integer.valueOf(value.toString());
                  fireTableCellUpdated(row, col);
              }
              catch (NumberFormatException e) {
                  log.log(Level.SEVERE, "The \"" + getColumnName(col) + "\" column accepts only integer values.");
              }
          }
          else {
              data[row][col] = value;
              fireTableCellUpdated(row, col);
          }
      }
docs: /*
  Don't need to implement this method unless your table's
  data can change.