Multiplication between two cells of a JTable in Java

Question

When I enter values in the cells of the 1st row of columns \"Units\" and \"Price\" , column \"Amount\"; the columns cell value should be set to the product of unit and amount .

Answer 1

The idea is to implement a TableModel so that it automatically returns the result of the product of unit and amount. Here is a small demonstration of what I mean (to add a new row, simply double click below the table):

import java.awt.BorderLayout;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.Vector;

import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.table.DefaultTableModel;

public class TestTable3 {

    protected void initUI() {
        final DefaultTableModel model = new DefaultTableModel() {

            @Override
            public Class<?> getColumnClass(int columnIndex) {
                switch (columnIndex) {
                case 0:
                    return Integer.class;
                case 1:
                case 2:
                    return Double.class;
                }
                return super.getColumnClass(columnIndex);
            }

            @Override
            public Object getValueAt(int row, int column) {
                if (column == 2) {
                    Integer i = (Integer) getValueAt(row, 0);
                    Double d = (Double) getValueAt(row, 1);
                    if (i != null && d != null) {
                        return i * d;
                    } else {
                        return 0.0;
                    }
                }
                return super.getValueAt(row, column);
            }

            @Override
            public boolean isCellEditable(int row, int column) {
                return column == 0 || column == 1;
            }

            @Override
            public void setValueAt(Object aValue, int row, int column) {
                super.setValueAt(aValue, row, column);
                fireTableCellUpdated(row, 2);
            }

            @Override
            public String getColumnName(int column) {
                switch (column) {
                case 0:
                    return "Quantity";
                case 1:
                    return "Price";
                case 2:
                    return "Total";
                }
                return super.getColumnName(column);
            }

            @Override
            public int getColumnCount() {
                return 3;
            }
        };
        final JTable table = new JTable(model);
        table.setFillsViewportHeight(true);
        table.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e) {
                if (e.getClickCount() == 2) {
                    if (table.rowAtPoint(e.getPoint()) < 0) {
                        model.addRow(new Vector());
                    }
                }
            }
        });
        model.addRow(new Vector());
        JFrame frame = new JFrame(TestTable3.class.getSimpleName());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JScrollPane scrollpane = new JScrollPane(table);
        frame.add(scrollpane, BorderLayout.CENTER);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException,
            UnsupportedLookAndFeelException {
        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                new TestTable3().initUI();
            }
        });
    }

}

And the result:

Answer 2

When I enter values in the cells of the 1st row of columns "Units" and "Price" , column "Amount"; the columns cell value should be set to the product of unit and amount

• have look at TableModelListener

• have to read the Oracle JTable tutorial