JTable - Help with updating a Text File

Question

Hi all,
I've been fighting this for a few days. I am trying to update a Text File with my JTable.... Displaying the data works great but when I try to edit a cell/field on the gui, I'm bombing out...... My text fiel is a small user control file with Id, Name,
Date, etc etc with the fields delimited with a "|".... I have built an Abstract Data Model (see below).... and I think my problem is in the setValueAt method.......
Thanks so much in advance!!!!
Mike
code:
import javax.swing.*;
import javax.swing.table.*;
import javax.swing.event.*;
import java.io.*;
import java.util.*;
public class DataFileTableModel extends AbstractTableModel {
protected Vector data;
protected Vector columnNames ;
protected String datafile;
public DataFileTableModel(String f){
datafile = f;
initVectors();
public void initVectors() {
String aLine ;
data = new Vector();
columnNames = new Vector();
try {
FileInputStream fin = new FileInputStream(datafile);
BufferedReader br = new BufferedReader(new InputStreamReader(fin));
// extract column names
StringTokenizer st1 =
new StringTokenizer(br.readLine(), "|");
while(st1.hasMoreTokens())
columnNames.addElement(st1.nextToken());
// extract data
while ((aLine = br.readLine()) != null) { 
StringTokenizer st2 =
new StringTokenizer(aLine, "|");
while(st2.hasMoreTokens())
data.addElement(st2.nextToken());
br.close();
catch (Exception e) {
e.printStackTrace();
public int getRowCount() {
return data.size() / getColumnCount();
public int getColumnCount(){
return columnNames.size();
public String getColumnName(int columnIndex) {
String colName = "";
if (columnIndex <= getColumnCount())
colName = (String)columnNames.elementAt(columnIndex);
return colName;
public Class getColumnClass(int columnIndex){
return String.class;
public boolean isCellEditable(int rowIndex, int columnIndex) {
return true;
public Object getValueAt(int rowIndex, int columnIndex) {
return (String)data.elementAt( (rowIndex * getColumnCount()) + columnIndex);
public void setValueAt(Object aValue, int rowIndex, int columnIndex) {
Vector rowVector=(Vector)data.elementAt(rowIndex);
rowVector.setElementAt(aValue, columnIndex);
fireTableCellUpdated(rowIndex,columnIndex);
// return;
}

Answer 1

No, the DefaultDataModel does not update the physical data file. It is just used to store the data as you type in the table cells.
The code from above is used to read data from a file and populate the DataModel.
Now you need to write another routine that will take the data from the DataModel and write it to your file. I have never actually done this but I think the code would be something like:
int rows = table.getModel().getRowCount();
int columns = table.getModel().getColumnCount();
//  Write column headers
for (int j = 0; j < columns; j++)
     TableColumn column = table.getColumnModel().getColumn(j);
        Object o = column.getHeaderValue();
     writeToFile( o.toString() + "|" );
writeToFile( "\n" );
// Write each row
for (int i = 0, i < rows; i++)
    for (int j = 0, j < columns; j++)
        Object o = table.getValueAt(i, j);
        writeToFile( o.toString + "|" );
    writeToFile( "\n" );
}If you need to update the file whenever data in a cell changes, then you could extend the DefaultTableModel and override the setValueAt() method to also write the contents of the DataModel to a file. But this is a lot of overhead since it rewrite the entire file for every cell change.