AWT List or JList ?
Hi everybody,
I am using javax.swing for my layout (buttons, textfields,..) but when I try to use JList and add some text to it (lstLog("hi");) I get this error:
symbol : method add(java.lang.String)
location: class javax.swing.JList
lstLog.add("hi");
1 error
BUILD FAILED (total time: 0 seconds)
But I don't get this error if I use another List from AWT, can u explain this to me pleas ? thank you!
Rkas wrote:
why not??Concrete answer: because it just doesn't exist, simple as that. Go to the JList API which you can find here and try to find a method called add(...). You won't find it because JList doesn't have this. It does however inherit an unrelated method of the same name from container (see below).
Theoretical answer: Swing handles things differently than AWT. With Swing all components have a non-GUI model which handle the logic of the component, and for JList that logic is maintaining the data list itself. So the GUI portion of JList doesn't worry about what data it holds, but its model, which usually is a DefaultListModel does worry about this information and can change the information with the appropriate method calls.
when I insert JList lstLog. in netbeans I get all the methodes of this component!! Yes, and I'm sure that it will display an "add" method, but understand that this method derives from Container (I wonder if NetBeans displays this information), and so has absolutely nothing to do with adding or removing items from a list.
so what do u mean by "JList doesn't" ??JList itself doesn't. Again, see the API.
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listModel2.addElement("100");
listModel2.addElement("80");
listModel2.addElement("50");
listModel2.addElement("10");
//Create the list and put it in a scroll pane
list = new JList(listModel);
list.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
list.setSelectedIndex(0);
list.addListSelectionListener(this);
JScrollPane listScrollPane = new JScrollPane(list);
//Create the percentlist and put it in a scroll pane
list2 = new JList(listModel2);
list2.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
list2.setSelectedIndex(0);
list2.addListSelectionListener(this);
JScrollPane listScrollPane2 = new JScrollPane(list2);
JButton hireButton = new JButton(hireString);
hireButton.setActionCommand(hireString);
hireButton.addActionListener(new HireListener());
fireButton = new JButton(fireString);
fireButton.setActionCommand(fireString);
fireButton.addActionListener(new FireListener());
employeeName = new JTextField(10);
employeeName.addActionListener(new HireListener());
String name = listModel.getElementAt(
list.getSelectedIndex()).toString();
employeeName.setText(name);
per = new JSlider(JSlider.HORIZONTAL, 0, 100, 50);
per.setMajorTickSpacing(10);
per.setPaintTicks(true);
per.setPaintLabels(true);
percent = new TextField(10);
percent.setValue(new Integer(1));
percent.addActionListener(new HireListener());
String name2 = listModel2.getElementAt(
list2.getSelectedIndex()).toString();
percent.setText(name2);
//Create a panel that uses FlowLayout (the default).
JPanel buttonPane = new JPanel();
buttonPane.add(employeeName);
buttonPane.add(per);
buttonPane.add(hireButton);
buttonPane.add(fireButton);
Container contentPane = getContentPane();
contentPane.add(listScrollPane, BorderLayout.CENTER);
contentPane.add(listScrollPane2, BorderLayout.EAST);
contentPane.add(buttonPane, BorderLayout.SOUTH);
class FireListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
//This method can be called only if
//there's a valid selection
//so go ahead and remove whatever's selected.
int index = list.getSelectedIndex();
int index2 = list2.getSelectedIndex();
listModel.remove(index);
listModel2.remove(index2);
int size = listModel.getSize();
int size2 = listModel2.getSize();
if (size == 0) {
//Nobody's left, disable firing.
fireButton.setEnabled(false);
} else {
//Adjust the selection.
if (index == listModel.getSize())//removed item in last position
index--;
list.setSelectedIndex(index); //otherwise select same index
if (size2 == 0) {
//Nobody's left, disable firing.
fireButton.setEnabled(false);
} else {
//Adjust the selection.
if (index2 == listModel2.getSize())//removed item in last position
index2--;
list2.setSelectedIndex(index2); //otherwise select same index
//This listener is shared by the text field and the hire button
class HireListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
//User didn't type in a name...
if (employeeName.getText().equals("")) {
Toolkit.getDefaultToolkit().beep();
return;
//User didn't type in a percent...
if (percent.getText().equals("")) {
Toolkit.getDefaultToolkit().beep();
return;
int index = list.getSelectedIndex();
int index2 = list2.getSelectedIndex();
int size = listModel.getSize();
int size2 = listModel2.getSize();
//If no selection or if item in last position is selected,
//add the new hire to end of list, and select new hire.
if (index == -1 || (index+1 == size)) {
listModel.addElement(employeeName.getText());
list.setSelectedIndex(size);
//Otherwise insert the new hire after the current selection,
//and select new hire.
} else {
listModel.insertElementAt(employeeName.getText(), index+1);
list.setSelectedIndex(index+1);
//If no selection or if item in last position is selected,
//add the new hire to end of list, and select new hire.
if (index2 == -1 || (index2+1 == size2)) {
listModel2.addElement(String.valueOf(per.getValue()));
list2.setSelectedIndex(size2);
//Otherwise insert the new hire after the current selection,
//and select new hire.
} else {
listModel2.insertElementAt(String.valueOf(per.getValue()), index2+1);
list2.setSelectedIndex(index2+1);
public void valueChanged(ListSelectionEvent e) {
if (e.getValueIsAdjusting() == false) {
if (list.getSelectedIndex() == -1) {
//No selection, disable fire button.
fireButton.setEnabled(false);
employeeName.setText("");
} else {
//Selection, update text field.
fireButton.setEnabled(true);
String name = list.getSelectedValue().toString();
employeeName.setText(name);
if (list2.getSelectedIndex() == -1) {
//No selection, disable fire button.
fireButton.setEnabled(false);
// percent.setText("");
} else {
//Selection, update text field.
fireButton.setEnabled(true);
String name = list2.getSelectedValue().toString();
// percent.setText(name);
public static void main(String s[]) {
JFrame frame = new ListDemo();
frame.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
frame.pack();
frame.setVisible(true);
} -
Short code causes a strange problem - About the list again -- please read!
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;_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 :-)
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