потому что вы написали эту строку кода из текущего класса, вы должны обернуть эти строки кода
внутри Class / void / constructor, например
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.table.*;
public class TableProcessing extends JFrame implements TableModelListener {
private static final long serialVersionUID = 1L;
private JTable table;
public TableProcessing() {
String[] columnNames = {"Item", "Quantity", "Price", "Cost"};
Object[][] data = {
{"Bread", new Integer(1), new Double(1.11), new Double(1.11)},
{"Milk", new Integer(1), new Double(2.22), new Double(2.22)},
{"Tea", new Integer(1), new Double(3.33), new Double(3.33)},
{"Cofee", new Integer(1), new Double(4.44), new Double(4.44)}
};
DefaultTableModel model = new DefaultTableModel(data, columnNames);
model.addTableModelListener(this);
table = new JTable(model) {
private static final long serialVersionUID = 1L;
@Override
public Class getColumnClass(int column) {
return getValueAt(0, column).getClass();
}
@Override
public boolean isCellEditable(int row, int column) {
int modelColumn = convertColumnIndexToModel(column);
return (modelColumn == 3) ? false : true;
}
};
table.setPreferredScrollableViewportSize(table.getPreferredSize());
JScrollPane scrollPane = new JScrollPane(table);
getContentPane().add(scrollPane);
}
@Override
public void tableChanged(TableModelEvent e) {
if (e.getType() == TableModelEvent.UPDATE) {
int row = e.getFirstRow();
int column = e.getColumn();
System.out.println(row + " : " + column);
if (column == 1 || column == 2) {
int quantity = ((Integer) table.getModel().getValueAt(row, 1)).intValue();
double price = ((Double) table.getModel().getValueAt(row, 2)).doubleValue();
Double value = new Double(quantity * price);
table.getModel().setValueAt(value, row, 3);
}
}
}
public static void main(String[] args) {
TableProcessing frame = new TableProcessing();
frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
}