Java自动计算表格某一数字列的和

[java]
package com.han;

import java.awt.BorderLayout;
import java.awt.Container;
import java.util.Vector;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.JTextField;
import javax.swing.event.TableModelEvent;
import javax.swing.event.TableModelListener;
import javax.swing.table.DefaultTableModel;

/**
* 自动计算表格某一数字列的和
* @author HAN
*
*/
public class TabelModelEvent_2 extends JFrame {

    /**
     *
     */
    private static final long serialVersionUID = 7045416728019138021L;

    float sum = 0;

    public TabelModelEvent_2() {
        // TODO Auto-generated constructor stub
        final Container container = getContentPane();
        JScrollPane scrollPane = new JScrollPane();
        Vector<String> tableNames = new Vector<String>();
        tableNames.add("数字列");
        Vector<Vector<String>> tableValues = new Vector<Vector<String>>();
        for (int i = 0; i < 4; i++) {
            Vector<String> vector = new Vector<String>();
            vector.add(null);
            tableValues.add(vector);
        }
        final DefaultTableModel defaultTabelModel = new DefaultTableModel(
                tableValues, tableNames);
        JTable table = new JTable(defaultTabelModel);
        scrollPane.setViewportView(table);
        container.add(scrollPane, BorderLayout.CENTER);
        JPanel panel = new JPanel();
        JLabel label = new JLabel("数字列总和：");
        final JTextField textField = new JTextField(10);
        panel.add(label);
        panel.add(textField);
        container.add(panel, BorderLayout.SOUTH);

        defaultTabelModel.addTableModelListener(new TableModelListener() {

            @Override
            public void tableChanged(TableModelEvent e) {
                // TODO Auto-generated method stub
                if (e.getType() == TableModelEvent.UPDATE) {
                    int row = e.getFirstRow();
                    int column = e.getColumn();

                    // keep that every cell value is float or null.
                    try {
                        Float.parseFloat((String) defaultTabelModel.getValueAt(
                                row, column));
                    } catch (NumberFormatException e1) {
                        JOptionPane.showMessageDialog(container,
                                "Your input object is not a float type");
                        defaultTabelModel.setValueAt(null, row, column);
                    } catch (NullPointerException e2) {
                        // do nothing
                    }

                    for (int i = 0; i < 4; i++) {
                        Object cellValue = defaultTabelModel.getValueAt(i, 0);
                        if (cellValue != null) {

                            float floatValue = Float
                                    .parseFloat((String) cellValue);
                            sum += floatValue;

                        }
                    }

补充：软件开发 , Java ,