Short code causes a strange problem - About the list again -- please read!

Question

Hi again people. Maybe you remember my project - has a list, that you can search thru using a text field. During the work I got stuck on a strange problem ( Again :-( ) My app has one text field, one combo box, one list and a text field once more. The code should do the following ->
*1. Load the list, no problem with that.*
*2. Show the elements of the list, that match the selected group in the combo box,no problem.*
*3. Search thru the list using the text field,no problem.*
4. When the user selects an element from the list, it should display its info in the second text field. This also works fine, but when after looking at info of one of the elements the things on numbers 2 and 3 ( look up! ) stop working. I must say that everything works fine until user selects an element from the list. I couldnt understand this kind of behavior so I am asking you to help me please.
The code is very simple:
import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
class the_window extends JFrame implements DocumentListener, ItemListener, ListSelectionListener {
    FileReader reader;
    String data_base[][];
    String first_pass[];
    int number_of_elements;
    DefaultListModel dflm = new DefaultListModel();
    JList list;
    JTextField text_field = new JTextField();
    JTextField info_field = new JTextField();
    String groups[] = {"1. group" , "2. group"};
    JComboBox groups_cmbx = new JComboBox(groups);
    the_window(){
        super("the Window!");
        JPanel panel = new JPanel(null);
        Container c = this.getContentPane();
        c.add(panel);
        text_field.setBounds(10,10,170,25);
        text_field.getDocument().addDocumentListener(this);
        panel.add(text_field);
        groups_cmbx.setBounds(10,45,170,25);
        groups_cmbx.addItemListener(this);
        panel.add(groups_cmbx);
        list = new JList(dflm);
        list.setBounds(10,90,170,190);
        list.setFixedCellHeight(20);
        list.addListSelectionListener(this);
        panel.add(list);
        info_field.setBounds(10,280,170,25);
        panel.add(info_field);
        load_the_base();
        refresh();
        this.setSize(190,350);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setResizable(false);
        this.setVisible(true);
    public void itemStateChanged(ItemEvent e){
        refresh();
    public void valueChanged(ListSelectionEvent e){
        String str = (String) dflm.getElementAt(list.getSelectedIndex());
        int index = 0;
        for(int i = 0; i < number_of_elements; i++){
            if(str.equals(data_base[0])){
index = i;
break;
info_field.setText(data_base[index][1]);
private void load_the_base(){
String data = "";
try{
reader = new FileReader("data.txt";);
int r = 0;
while((r = reader.read()) != -1){
char c = (char) r;
data += c;
reader.close();
}catch(IOException e){}
first_pass = data.split(";");
number_of_elements = first_pass.length;
data_base = new String[number_of_elements][];
for(int i = 0; i<number_of_elements; i++){
data_base[i] = first_pass[i].split("#");
private void refresh(){
String search_str = text_field.getText();
int selektovano = groups_cmbx.getSelectedIndex();
dflm.clear();
for(int i = 0; i < number_of_elements; i++){
int grupa = Integer.parseInt(data_base[i][2]);
if(grupa == selektovano){
String at_the_moment = data_base[i][0]; // if you change this to String at_the_moment = data_base[i][1]; it works perfectly
if(at_the_moment.startsWith(search_str)){
dflm.addElement(at_the_moment);
public void changedUpdate(DocumentEvent e){
refresh();
public void removeUpdate(DocumentEvent e){
refresh();
public void insertUpdate(DocumentEvent e){
refresh();
public class Main {
public static void main(String[] args) {
JFrame f = new the_window();
Now, can you please tell me whats wrong with this?
For the "data.txt" make a new text file using *notepad* and copy the following line into the document:
_1. element#1. info#0;2. element#2. info#0;3. element#3. info#1;4. element#4. info#1;5. element#5. info#1;_                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           

Answer 1

Darryl.Burke wrote:
Keith, thanks for making that readable. So here's the diagnosis -
In the refresh() method, calling defaultListModel.clear() results in a valueChanged(...) event in which this method calldefaultListModel.getElementAt(list.getSelectedIndex())results in the exception noted, as getSelectedIndex returns -1, the list being empty... you can't getElementAt(-1).
I haven't analyzed all the code nor checked whether is now works as desired, but this small change to valueChanged counters the exception being thrown.   public void valueChanged(ListSelectionEvent e) {
infoField.setText(""); // do this unconditionally
if (list.getSelectedIndex() != -1) {
String value = (String)defaultListModel.getElementAt(list.getSelectedIndex());
for(int i = 0; i < numFields; i++){
if(value.equals(matrix[0])){
infoField.setText(matrix[i][1]);
break;
db
Yea! You were right! I didnt think that calling *list_model.clear();* will result in calling *valueChanged()* ........
That was some *clear()* thinking :-) Thank you!
corlettk wrote:
I cleaned up some variable & method names (tut tut), imports (very naighty), and some thread stuff... but it remains fundamentally the same codeIs it so important to "clean" the imports? How much does it slow down the loading time? Should I do this on all my projects, because they are all "very naighty"?
ps. Thanks to all that gave some help to answering this strange question :-)