Swing: when trying to get the values from a JTable inside an event handler

Question

Hi,
I am trying to write a graphical interface to compute the Gauss Elimination procedure for solving linear systems. The class for computing the output of a linear system already works fine on console mode, but I am fighting a little bit to make it work with Swing.
I put two buttons (plus labels) and a JTextField . The buttons have the following role:
One of them gets the value from the JTextField and it will be used to the system dimension. The other should compute the solution. I also added a JTable so that the user can type the values in the screen.
So whenever the user hits the button Dimensiona the program should retrieve the values from the table cells and pass them to a 2D Array. However, the program throws a NullPointerException when I try to
do it. I have put the code for copying this Matrix inside a method and I call it from the inner class event handler.
I would thank you very much for the help.
Daniel V. Gomes
here goes the code:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import AdvanceMath.*;
public class MathF2 extends JFrame {
private JTextField ArrayOfFields[];
private JTextField DimOfSis;
private JButton Calcular;
private JButton Ativar;
private JLabel label1;
private JLabel label2;
private Container container;
private int value;
private JTable DataTable;
private double[][] A;
private double[] B;
private boolean dimensionado = false;
private boolean podecalc = false;
public MathF2 (){
super("Math Calcs");
Container container = getContentPane();
container.setLayout( new FlowLayout(FlowLayout.CENTER) );
Calcular = new JButton("Resolver");
Calcular.setEnabled(false);
Ativar = new JButton("Dimensionar");
label1 = new JLabel("Clique no bot�o para resolver o sistema.");
label2 = new JLabel("Qual a ordem do sistema?");
DimOfSis = new JTextField(4);
DimOfSis.setText("0");
JTable DataTable = new JTable(10,10);
container.add(label2);
container.add(DimOfSis);
container.add(Ativar);
container.add(label1);
container.add(Calcular);
container.add(DataTable);
for ( int i = 0; i < 10 ; i ++ ){
for ( int j = 0 ; j < 10 ; j++) {
DataTable.setValueAt("0",i,j);
myHandler handler = new myHandler();
Calcular.addActionListener(handler);
Ativar.addActionListener(handler);
setSize( 500 , 500 );
setVisible( true );
public static void main ( String args[] ){
MathF2 application = new MathF2();
application.addWindowListener(
new WindowAdapter(){
public void windowClosing (WindowEvent event)
System.exit( 0 );
private class myHandler implements ActionListener {
public void actionPerformed ( ActionEvent event ){
if ( event.getSource()== Calcular ) {
if ( event.getSource()== Ativar ) {
//dimensiona a Matriz A
if (dimensionado == false) {
if (DimOfSis.getText()=="0") {
value = 2;
} else {
value = Integer.parseInt(DimOfSis.getText());
dimensionado = true;
Ativar.setEnabled(false);
System.out.println(value);
} else {
Ativar.setEnabled(false);
Calcular.setEnabled(true);
podecalc = true;
try {
InitValores( DataTable, value );
} catch (Exception e) {
System.out.println("Erro ao criar matriz" + e );
private class myHandler2 implements ItemListener {
public void itemStateChanged( ItemEvent event ){
private void InitValores( JTable table, int n ) {
A = new double[n][n];
B = new double[n];
javax.swing.table.TableModel model = table.getModel();
for ( int i = 0 ; i < n ; i++ ){
for (int j = 0 ; j < n ; j++ ){
Object temp1 = model.getValueAt(i,j);
String temp2 = String.valueOf(temp1);
A[i][j] = Double.parseDouble(temp2);

Answer 1

What I did is set up a :
// This code will setup a listener for the table to handle a selection
players.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
ListSelectionModel rowSM = players.getSelectionModel();
rowSM.addListSelectionListener(new Delete_Player_row_Selection(this));
//Class will take the event and call a method inside the Delete_Player object.
class Delete_Player_row_Selection
implements javax.swing.event.ListSelectionListener
Delete_Player adaptee;
Delete_Player_row_Selection (Delete_Player temp)
adaptee = temp;
public void valueChanged (ListSelectionEvent listSelectionEvent)
adaptee.row_Selection(listSelectionEvent);
in the row_Selection function
if(ex.getValueIsAdjusting()) //To remove double selection
return;
ListSelectionModel lsm = (ListSelectionModel) ex.getSource();
if(lsm.isSelectionEmpty())
System.out.println("EMtpy");
else
int selected_row = lsm.getMinSelectionIndex();
ResultSetTableModel model = (ResultSetTableModel) players.getModel();
String name = (String) model.getValueAt(selected_row, 1);
Integer id = (Integer) model.getValueAt(selected_row, 3);
This is how I got info out of a table when the user selected it