Jtable doesn't refresh/update data

Question

I have a problem with JTable/JScrollPane. My data table is not refreshing/updating. I am using DefultTableModel and according to the code everything is fine and I don't have any errors. Also I have a table with paging and that's why I am using action listeners and buttons "prev" and "next". I am passing from other function to function that is coded in class where is JTable. Problem is that I fill arrays which contains data for table but table won't update/refresh it. Here is my code. Thanks advance.

BIG EDIT Old code was removed. I added new codes that will help you guys/girls to understand problem that I have. Hope that this will help. Regards.

First here is class that show gui:

import javax.swing.*;
public class Glavni {
public static void main(String[] args)  {
    // TODO Auto-generated method stub
    SwingUtilities.invokeLater(new Runnable() {
        public void run() {
                gui Scanner = new gui();
                Scanner.setVisible(true);
        }
    });
}

}

Second here is class that pass String to gui class that contains jtable

public class passDatatoTable {
public void passData(){
    String str1,str2,str3,str4;
    gui SendStringsToGUI = new gui();
    for (int i =0;i<=10;i++){
            str1="Column 1 of row: "+i;
            str2="Column 2 of row: "+i;
            str3="Column 3 of row: "+i;
            str4="Column 4 of row: "+i;
            SendStringsToGUI.WriteMonitorData(str1, str2, str3, str4);

    }
  }
}

Next here is declaration of gui (contructor):

import javax.swing.*;
import javax.swing.table.DefaultTableModel;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class gui extends JFrame implements ActionListener {
private static final long serialVersionUID = 1L;
 String[][] data = new String[100][4];

 String[] columnNames = new String[]{
         "IP", "PC_NAME", "ttl", "db"
 };
 DefaultTableModel model = new DefaultTableModel(data,columnNames);


    JTable table =  new JTable(model);
    JScrollPane scrollPane = new JScrollPane(table);
    int i=0;
public void WriteMonitorData (String IP, String PC_NAME, String ttl, String gw)
{
    System.out.println(IP);//just for testing (check if data was passed)
    model.setValueAt(IP, i, 0);
    model.setValueAt(PC_NAME, i, 1);
    model.setValueAt(ttl, i, 2);
    model.setValueAt(gw, i, 3);

    i++;
    model.fireTableDataChanged();
    table.repaint();
    scrollPane.repaint();

}   
gui(){

JButton addData= new JButton("Add Data");
JButton next = new JButton("next");
JButton prev = new JButton("prev");
addData.addActionListener(this);
next.addActionListener(this);
prev.addActionListener(this);
JPanel panel = new JPanel(new BorderLayout());
JPanel buttonPanel = new JPanel();
buttonPanel.add(addData);
buttonPanel.add(prev);
buttonPanel.add(next);
panel.add(buttonPanel, BorderLayout.SOUTH);
panel.add(table.getTableHeader(), BorderLayout.PAGE_START);
panel.add(scrollPane, BorderLayout.CENTER);
getContentPane().add(panel);
}

Here is actionListeners:

public void actionPerformed(ActionEvent e) {
if ("Add Data".equals(e.getActionCommand())){

        passDatatoTable passSomeData = new passDatatoTable();
        passSomeData.passData();
              }
 if ("next".equals(e.getActionCommand())) {
         Rectangle rect = scrollPane.getVisibleRect();
         JScrollBar  bar = scrollPane.getVerticalScrollBar();
         int blockIncr = scrollPane.getViewport().getViewRect().height;
             bar.setValue(bar.getValue() + blockIncr);
             scrollPane.scrollRectToVisible(rect);
     }
     if ("prev".equals(e.getActionCommand())) {
         Rectangle rect = scrollPane.getVisibleRect();
         JScrollBar  bar = scrollPane.getVerticalScrollBar();
         int blockIncr = scrollPane.getViewport().getViewRect().height;
             bar.setValue(bar.getValue() - blockIncr);
             scrollPane.scrollRectToVisible(rect);
     }

  }

Answer 1

Your first snippet shows this:

JTable table = new JTable(model);

but your gui() constructor shows:

JTable table = new JTable(data, columnNames);

You initiate the table twice. Once using the TableModel (JTable(TableModel tm)) the next using JTable(int rows,int cols) this is not good, initiate the JTable once in the constructor:

gui() {
DefaultTableModel model = new DefaultTableModel(data,columnNames);
JTable table =  new JTable(model);
JScrollPane scrollPane = new JScrollPane(table);

JButton next = new JButton("next");
JButton prev = new JButton("prev");
next.addActionListener(this);
prev.addActionListener(this);
JPanel panel = new JPanel(new BorderLayout());
JPanel buttonPanel = new JPanel();
buttonPanel.add(prev);
buttonPanel.add(next);
panel.add(buttonPanel, BorderLayout.SOUTH);
panel.add(table.getTableHeader(), BorderLayout.PAGE_START);
panel.add(scrollPane, BorderLayout.CENTER);
getContentPane().add(panel);
}

UPDATE:

Here is an example that has a thread which will start 2.5 secinds after the UI is visible and change a value of the JTable:

import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.*;
import javax.swing.table.DefaultTableModel;

public class Test extends JFrame {

    public static void main(String[] args) throws Exception {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                new Test().createAndShowUI();
            }
        });

    }

    private void createAndShowUI() {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        initComponents(frame);
        frame.pack();
        frame.setVisible(true);
        new Thread(new Runnable() {

            @Override
            public void run() {
                try {
                    Thread.sleep(2500);
                } catch (InterruptedException ex) {
                    Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
                } 
                SwingUtilities.invokeLater(new Runnable() {

                     @Override
                     public void run() {
                       model.setValueAt("hello", 0, 0);
                     }
                });
            }
        }).start();
    }
    static DefaultTableModel model;

    private void initComponents(JFrame frame) {

        String data[][] = {
            {"1", "2", "3"},
            {"4", "5", "6"},
            {"7", "8", "9"},
            {"10", "11", "12"}
        };

        String col[] = {"Col 1", "Col 2", "Col 3"};

        model = new DefaultTableModel(data, col);
        JTable table = new JTable(model);

        frame.getContentPane().add(new JScrollPane(table));
    }
}

Answer 2

From what I understand from the comments and the question, you have first created a DefaultTableModel by passing the data as arrays in the constructor

String[][] data = new String[100][4];
String[] columnNames = new String[]{
     "IP", "PC_NAME", "ttl", "db"};
DefaultTableModel model = new DefaultTableModel(data,columnNames);

and you try to modify the table afterwards by adjusting those arrays. That will never ever have any effect, as the DefaultTableModel does not use those arrays. This can be seen in the source code of that class

public DefaultTableModel(Object[][] data, Object[] columnNames) {
    setDataVector(data, columnNames);
}

which in the end comes down to

protected static Vector convertToVector(Object[][] anArray) {
    if (anArray == null) {
        return null;
    }
    Vector<Vector> v = new Vector<Vector>(anArray.length);
    for (Object[] o : anArray) {
        v.addElement(convertToVector(o));
    }
    return v;
}

So all the elements of the array are copied into an internal Vector and the array is no longer used.

Solution: do not update the arrays but update the DefaultTableModel. That class provides all the API you need to add/remove data to/from it.