Using a JList

Hi everyone! Happy new year.
Okay, I have some work for some keen programmer out there to do. There are 10 duke dollars avaliable to whoever can help me with this problem.
I am using a JList to display a list of milestones which are required later on in my project. When no item is selected from the list, I want the 'Delete Milestone' button to automatically disable and when an item is selected from the list, I want it to auto enable. If the list is empty, then the button should remain disabled. For this to work I think I need some sort of ListSelectionListener but I am not sure how to do this. At the moment I get an exception whenever I click on the 'Delete Milestone' button and no selection has been made, which is understandable.
Another thing that I need doing is that if a milestone is added to the list, and the 'Critical Milestone' is selected, then whenever that item is selected from the list, the background colour should be red; whenever a 'Non-critical Milestone' is created, then that should remain with a yellow background whenever selected from the list. At the moment, the background colour changes to whatever the last added milestone happened to be - either red or yellow for all entries that have been added to the list. If anyone can help me with this then that would be really appreciated and very helpful. The 4 files can be found below - just run the 'AddMilestoneTest' class to start the app. Thanks.
* AddMilestoneTest.java
* 29/12/02 (Date start)
* This class is for iteration purposes for
* the "Add Milestone" wizard
import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
public class AddMilestoneTest extends JPanel
private JButton addMilestoneButton;
public JFrame addMilestoneFrame;
static AddMilestoneTest instance;
public AddMilestoneTest()
instance = this;
// create new button
addMilestoneButton = new JButton("Add Milestone");
// create tooltip for every button
addMilestoneButton.setToolTipText("Add Milestone");
// add our button to the JPanel
add(addMilestoneButton);
// construct button action
AddMilestoneListener listener1 = new AddMilestoneListener();
// Add action listener to button
addMilestoneButton.addActionListener(listener1);
private class AddMilestoneListener implements ActionListener
public void actionPerformed(ActionEvent evt)
addMilestoneFrame = new JFrame("Add Milestone Wizard*");
MilestoneSplitPanel milestoneSplitPanel = new MilestoneSplitPanel();
addMilestoneFrame.getContentPane().add(milestoneSplitPanel);
addMilestoneFrame.setSize(850, 305);
addMilestoneFrame.setVisible(true);
// Main entry point into the program
public static void main(String[] args)
// Create a frame to hold us and set its title
JFrame frame = new JFrame("Add Milestone Iteration");
// Set frame to close after user request
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// Add our panel to the frame
AddMilestoneTest amt = new AddMilestoneTest();
frame.getContentPane().add(amt, BorderLayout.CENTER);
// Resize the frame
frame.setSize(680, 480);
// Make the windows visible
frame.setVisible(true);
* MilestoneSplitPanel.java
* 29/12/02
* This class creates a split between the
* AddMilestonePanel and the CurrentMilestonePanel
import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;
import java.awt.event.*;
public class MilestoneSplitPanel extends JPanel
// Declare a split panel
JSplitPane splitPanel;
// Declare the panels required here
AddMilestonePanel addMilestonePanel;
CurrentMilestonePanel currentMilestonePanel;
public MilestoneSplitPanel()
// Create the panels required
addMilestonePanel = new AddMilestonePanel();
currentMilestonePanel = new CurrentMilestonePanel();
// Create the split panel with our two panels
splitPanel = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT, currentMilestonePanel, addMilestonePanel);
splitPanel.setDividerLocation(200);
//Provide minimum sizes for the two components in the split pane
addMilestonePanel.setMinimumSize(new Dimension(350, 200));
currentMilestonePanel.setMinimumSize(new Dimension(100, 100));
//Add the split panel to this panel.
add(splitPanel, BorderLayout.CENTER);
* AddMilestonePanel.java
* 29/12/02 (Date start)
* This class is for iteration purposes for
* the "Add Milestone" wizard
import javax.swing.*;
import javax.swing.border.*;
import java.awt.*;
import java.awt.event.*;
public class AddMilestonePanel extends JPanel
private JLabel milestoneNameLabel;
private JLabel milestoneNameMaxChar;
private JLabel milestoneECDLabel;
private JLabel forwardSlash1;
private JLabel forwardSlash2;
private JLabel dateFormatLabel;
private JLabel selectOne;
private JTextField milestoneName;
private JComboBox theDate;
private JComboBox theMonth;
private JComboBox theYear;
private ButtonGroup group;
private JRadioButton criticalMilestone;
private JRadioButton nonCriticalMilestone;
private JButton addMilestone;
private JButton deleteMilestone;
private JButton cancel;
private JButton finish;
private JList currentMilestones;
static AddMilestonePanel instance;
public String dateSelected;
public String monthSelected;
public String yearSelected;
public AddMilestonePanel()
instance = this;
// create additional panels to hold objects
JPanel topPanel = new JPanel();
JPanel middlePanel = new JPanel();
JPanel lowerPanel = new JPanel();
JPanel buttonPanel = new JPanel();
// Create a border around the "toppanel"
Border etched = BorderFactory.createBevelBorder(BevelBorder.RAISED, Color.black, Color.blue);
Border titled = BorderFactory.createTitledBorder(etched, "Provide a name for the milestone");
topPanel.setBorder(titled);
// Create a border around the "middlepanel"
Border etched1 = BorderFactory.createBevelBorder(BevelBorder.RAISED, Color.black, Color.blue);
Border titled1 = BorderFactory.createTitledBorder(etched1, "Enter an estimated completion date of the milestone");
middlePanel.setBorder(titled1);
// Create a border around the "lowerpanel"
Border etched2 = BorderFactory.createBevelBorder(BevelBorder.RAISED, Color.black, Color.blue);
Border titled2 = BorderFactory.createTitledBorder(etched2, "Choose whether the milestone is critical or non-critical");
lowerPanel.setBorder(titled2);
// initialise JLabel objects
milestoneNameLabel = new JLabel("Milestone Name: ");
milestoneNameMaxChar = new JLabel("(Max 20 chars)");
milestoneECDLabel = new JLabel("Estimated Completion Date: ");
forwardSlash1 = new JLabel("/");
forwardSlash2 = new JLabel("/");
dateFormatLabel = new JLabel("(Date/Month/Year)");
selectOne = new JLabel("(Select One)");
// create textfield for the milestone name
milestoneName = new JTextField(20);
milestoneName.setColumns(15);
topPanel.validate();
// create the combo boxes for the date
theDate = new JComboBox(new String[]
"01", "02", "03", "04", "05", "06", "07", "08", "09", "10", "11", "12", "13", "14", "15", "16",
"17", "18", "19", "20", "21", "22", "23", "24", "25", "26", "27", "28", "29", "30", "31"
theDate.setEditable(false);
theMonth = new JComboBox(new String[]
"01", "02", "03", "04", "05", "06", "07", "08", "09", "10", "11", "12"
theMonth.setEditable(false);
theYear = new JComboBox(new String[]
"2001", "2002", "2003", "2004", "2005", "2006", "2007", "2008", "2009", "2010", "2011", "2012"
theYear.setEditable(false);
// create the radio buttons and add them to the group
group = new ButtonGroup();
criticalMilestone = new JRadioButton("Critical Milestone", true);
nonCriticalMilestone = new JRadioButton("Non-critical Milestone", false);
group.add(criticalMilestone);
group.add(nonCriticalMilestone);
// create the buttons
addMilestone = new JButton("Add Milestone", new ImageIcon("D:/My Uni Work/Final Year Project/Graphics/addMilestoneIcon.JPG"));
deleteMilestone = new JButton("Delete Milestone", new ImageIcon("D:/My Uni Work/Final Year Project/Graphics/deleteMilestone.JPG"));
cancel = new JButton("Cancel", new ImageIcon("D:/My Uni Work/Final Year Project/Graphics/StopControl.gif"));
finish = new JButton("Finish", new ImageIcon("D:/My Uni Work/Final Year Project/Graphics/bluearrow.gif"));
// set tooltips for buttons
addMilestone.setToolTipText("Add Milestone");
deleteMilestone.setToolTipText("Delete Milestone");
cancel.setToolTipText("Cancel");
finish.setToolTipText("Finish");
// set the state of the buttons when first run
deleteMilestone.setEnabled(false);
finish.setEnabled(false);
// add objects to panels
topPanel.add(milestoneNameLabel);
topPanel.add(milestoneName);
topPanel.add(milestoneNameMaxChar);
middlePanel.add(milestoneECDLabel);
middlePanel.add(theDate);
middlePanel.add(forwardSlash1);
middlePanel.add(theMonth);
middlePanel.add(forwardSlash2);
middlePanel.add(theYear);
middlePanel.add(dateFormatLabel);
lowerPanel.add(criticalMilestone);
lowerPanel.add(nonCriticalMilestone);
lowerPanel.add(selectOne);
buttonPanel.add(addMilestone);
buttonPanel.add(deleteMilestone);
buttonPanel.add(cancel);
buttonPanel.add(finish);
// use Box layout to arrange panels
Box hbox1 = Box.createHorizontalBox();
hbox1.add(topPanel);
Box hbox2 = Box.createHorizontalBox();
hbox2.add(middlePanel);
Box hbox3 = Box.createHorizontalBox();
hbox3.add(lowerPanel);
Box hbox4 = Box.createHorizontalBox();
hbox4.add(buttonPanel);
Box vbox = Box.createVerticalBox();
vbox.add(hbox1);
vbox.add(Box.createGlue());
vbox.add(hbox2);
vbox.add(Box.createGlue());
vbox.add(hbox3);
vbox.add(Box.createGlue());
vbox.add(hbox4);
this.add(vbox, BorderLayout.NORTH);
// create instance of cancelButtonListener
CancelButtonListener cancelListen = new CancelButtonListener();
// create instance of AddMilestoneListener
AddMilestoneListener milestoneListener = new AddMilestoneListener();
// create instance of DeleteMilestoneListener
DeleteMilestoneListener deleteListener = new DeleteMilestoneListener();
// add actionListener for the buttons
cancel.addActionListener(cancelListen);
addMilestone.addActionListener(milestoneListener);
deleteMilestone.addActionListener(deleteListener);
private class CancelButtonListener implements ActionListener
public void actionPerformed(ActionEvent event)
Object source = event.getSource();
if(source == cancel)
AddMilestoneTest.instance.addMilestoneFrame.setVisible(false);
private class AddMilestoneListener implements ActionListener
public void actionPerformed(ActionEvent event)
String milestoneNameText = milestoneName.getText().trim();
int textSize = milestoneNameText.length();
dateSelected = (String)theDate.getSelectedItem();
monthSelected = (String)theMonth.getSelectedItem();
yearSelected = (String)theYear.getSelectedItem();
if(textSize > 20)
//display a JOptionPane
JOptionPane.showMessageDialog(AddMilestonePanel.instance, "You have entered a title that is greater than 20 characters.",
"Text too Long", JOptionPane.ERROR_MESSAGE);
else if(textSize == 0)
//display a JOptionPane
JOptionPane.showMessageDialog(AddMilestonePanel.instance, "You have not entered a milestone name. Please do so (Maximum 20 Characters).",
"No Project Name Entered", JOptionPane.ERROR_MESSAGE);
else if(dateSelected == "30" && monthSelected == "02" || dateSelected == "31" && monthSelected == "02" || dateSelected == "31" && monthSelected == "04" ||
dateSelected == "31" && monthSelected == "06" || dateSelected == "31" && monthSelected == "09" || dateSelected == "31" && monthSelected == "11")
JOptionPane.showMessageDialog(AddMilestonePanel.instance, "You have selected an invalid date. Re-check that the date is valid.",
"Invalid Date Selected", JOptionPane.ERROR_MESSAGE);
} // ANOTHER CHECK IS REQUIRED HERE WHEN INTEGRATING - IF DATE ENETERED IS WITHIN THE START DATE AND END DATE OF THE PROJECT
else
deleteMilestone.setEnabled(true);
finish.setEnabled(true);
if(criticalMilestone.isSelected())
CurrentMilestonePanel.instance.listModel.addElement(milestoneNameText);
CurrentMilestonePanel.instance.currentMilestoneList.setSelectionBackground(Color.red);
else if(nonCriticalMilestone.isSelected())
CurrentMilestonePanel.instance.listModel.addElement(milestoneNameText);
CurrentMilestonePanel.instance.currentMilestoneList.setSelectionBackground(Color.yellow);
private class DeleteMilestoneListener implements ActionListener
public void actionPerformed(ActionEvent event)
if(CurrentMilestonePanel.instance.listModel.size() > 0)
int selectedItemIndex = CurrentMilestonePanel.instance.currentMilestoneList.getSelectedIndex();
CurrentMilestonePanel.instance.listModel.remove(selectedItemIndex);
* CurrentMilestonePanel.java
* 29/12/02 (Date start)
* This class is for iteration purposes for
* the "Add Milestone" wizard
import javax.swing.*;
import javax.swing.border.*;
import java.awt.*;
import java.awt.event.*;
public class CurrentMilestonePanel extends JPanel
public JList currentMilestoneList;
private JLabel currentMilestonesAdded;
// List Model that will hold the data for the list
public DefaultListModel listModel;
// Scroll pane that will contain the list
private JScrollPane scrollPaneList;
static CurrentMilestonePanel instance;
// Constructor
public CurrentMilestonePanel()
instance = this;
// create label
currentMilestonesAdded = new JLabel("Current Milestones Added");
listModel = new DefaultListModel();
//listModel.addElement("No Milestones Added");
// Create the list
currentMilestoneList = new JList(listModel);
// Set single selection, and select the first item
currentMilestoneList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
currentMilestoneList.setSelectedIndex(0);
// Create a scroll panel to hold list
scrollPaneList = new JScrollPane(currentMilestoneList);
// Set the preferred size
scrollPaneList.setPreferredSize(new Dimension(130, 200));
//Add the scroll pane to this panel.
add(currentMilestonesAdded, BorderLayout.NORTH);
add(scrollPaneList, BorderLayout.CENTER);

I suggest that you look into the swing tutorial. There are some samples of how to write ListSelectionListener.
I quickly scanned your code for the DeleteMilestoneListener. You get an exception here because you don't check if an item is selected in the list.

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Even when i pass it an integer constant, i get the
exceptionA couple of things:
First of all, the remove(int) method defined in JList is inherited from java.awt.Container: it is used for removing a child Component with the given index from a Container. In other words, you cannot use it to remove items from the list.
In fact, there are no methods defined in the JList API for adding or removing items once the list is created. This is because the ListModel interface that defines the data that backs the JList is immutable.
It is still possible, of course, to add and remove items from a JList. The trick is to use a custom ListModel implementation, such as DefaultListModel, that allows such modifications. See the JList tutorial for examples of this.
Secondly, if something is selected in the list, getSelectedIndex() will not return -1. If the JList you see on your screen has something selected, but getSelectedIndex() returns -1 when called on a JList reference in your code, then chances are good that you have two different JList objects. The JList that you add to the UI is not the same JList instance you refer to when calling getSelectedIndex().

Reorder items in JTree using drag-and-drop

Title says it all: before I start re-inventing the wheel, any code out there?
Think of the code that I need as an outliner.

Did you ever find a solution to this. I'm looking to implement a similar interface using a JList where the user can reorder drawing layers by dragging and dropping.
I'm temped to use a scrollpane and roll my own drag reorder code, so any supported behaviors would be welcome.
thanks,
Steven

Changing JList cell renderer on selection

Hi,
In our application we need to change the renderer of the selected cell of JList to JTextArea while maintaining default cell renderer for unselected cells. I tried by providing custom cell renderer (code is given below) but it does not work..:-(. Though the component used by JList for rendering the cell is JTextArea, the height of the cell remains same as that of unselected cells. Our requirement is to change the cell height of the selected row so as to give a feel that selected row expands and shows some more information about the selected item to the user.
Here is the code snippet of the cell renderer that I wrote:
class CellRenderer1 extends DefaultListCellRenderer{
private JTextArea selTxtArea;
CellRenderer1() {
selTxtArea = new JTextArea(3,20);
this.setOpaque(true);
public Component getListCellRendererComponent(JList list,
Object value, int index,
boolean isSelected, boolean cellHasFocus) {
String name = (String) value;
if ( isSelected ) {
selTxtArea.setBackground(list.getSelectionBackground());
selTxtArea.setForeground(list.getSelectionForeground());
selTxtArea.setText(name + "\n" + name);
return selTxtArea;
else {
this.setBackground(list.getBackground());
this.setForeground(list.getForeground());
this.setText(name);
return this;
//return this;
Any pointers or help will be highly appreciated.
Thanks
Atul

JList calculates fixedCellHeight and then uses the same for every cell. This was causing the problem. By overriding the getRowHeight method of BasicListUI class I was able to achieve different cell heights for selected and unselected rows. Following is the code snippet which shows how this was achieved:
protected int getRowHeight(int row) {
if ( (cellHeights == null) || (cellHeights.length < row )) {
cellHeights = new int[row];
ListModel model = list.getModel();
Object value = model.getElementAt(row);
ListSelectionModel selModel = list.getSelectionModel();
boolean isSelected = selModel.isSelectedIndex(row);
Component comp = list.getCellRenderer().
getListCellRendererComponent( list, value, row,
isSelected, false);
Dimension dim = comp.getPreferredSize();
int height = dim.height;
cellHeights[row] = height;
return cellHeights[row];
}

Jlist as a Cell Renderer

Hi ,
I would reaally appreciate if someone could post an example of using a JList as a custom Cell renderer
Thank you.

Here's a start (I couldn't be bothered to set an editor too):import java.awt.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.table.*;
public class Test extends JFrame {
    public Test () {
        JTable table = new JTable (new TestTableModel ());
        table.setDefaultRenderer (Integer[].class, new TestTableCellRenderer ());
        table.setRowHeight (50);
        getContentPane ().setLayout (new BorderLayout ());
        getContentPane ().add (new JScrollPane (table));
        setDefaultCloseOperation (DISPOSE_ON_CLOSE);
        setTitle ("Test");
        pack ();
        setLocationRelativeTo (null);
        setVisible (true);
    public static void main (String[] parameters) {
        new Test ();
    private class TestTableModel implements TableModel {
        private final static int N = 10;
        private Object[][] data;
        private ColumnData[] columnData;
        public TestTableModel () {
            data = new Object[N][2];
            for (int i = 0; i < N; i ++) {
                data[0] = new Integer (i);
data[i][1] = new Integer[i + 1];
for (int j = 0; j <= i; j ++) {
((Integer[]) data[i][1])[j] = new Integer (j);
columnData = new ColumnData[] {
new ColumnData ("n", Integer.class),
new ColumnData ("0..n", Integer[].class)
public int getColumnCount () {
return columnData.length;
public int getRowCount () {
return data.length;
public boolean isCellEditable (int row, int column) {
return false;
public void setValueAt (Object value, int row, int column) {}
public Class getColumnClass (int column) {
return columnData[column].classType;
public Object getValueAt (int row, int column) {
return data[row][column];
public String getColumnName (int column) {
return columnData[column].name;
public void addTableModelListener (TableModelListener listener) {}
public void removeTableModelListener(TableModelListener listener) {}
private class ColumnData {
public String name;
public Class classType;
public ColumnData (String name, Class classType) {
this.name = name;
this.classType = classType;
private class TestTableCellRenderer extends JScrollPane implements TableCellRenderer {
private JList list;
public TestTableCellRenderer () {
list = new JList ();
setViewportView (list);
public Component getTableCellRendererComponent (JTable table, Object value, boolean selected, boolean focused, int row, int column) {
list.setListData ((Integer[]) value);
return this;
Kind regards,
  Levi

Strange repaint behaviour with JList & Keyboard actions

Hi everyone,
This is my first post to the forum. You guys have been a great help in the past and I hope to contribute more in the future.
Anyways, I've encountered some strange repainting behaviour with a JDialog that uses a JList and a JButton. The dialog is fairly straight-forward and basically this is how it works (like an open file dialog - yes I'm implementing my own filechooser of sorts):
* JList lists a number of simple items that the user can select from.
* Once a selection is made, an Open button (JButton) is enabled.
* <ENTER> key is registered (using registerKeyboardAction()) with a JPanel which is used as the main content pane in the dialog.
* The user can either click on the Open Button or hit the <ENTER> key which then closes the dialog and runs whatever logic that needs to.
Now, the repaint problem comes in when:
1. User selects an item.
2. User hits the <ENTER> button
3. Dialog closes
4. User brings the dialog back up. This entails reloading the list by removing all elements from the list and adding new ones back in.
5. Now... if the user uses the mouse to select an item lower in the list than what was done in step #1, the selection is made, but the JList doesn't repaint to show that the new selection was made.
I didn't include a code sample because the dialog setup is totally straight-forward and I'm not doing anything trick (I've been doing this kind of thing for years now).
If I remove the key registration for the <ENTER> key from the dialog, this problem NEVER happens. Has anyone seen anything like this? It's a minor problem since my workaround is to use a ListSelectionListener which manually calls repaint() on the JList inside the valueChanged() method.
Just curious,
Huy

Oh, my bad. I'm actually using a JToggleButton and not a JButton, so the getRootPane().setDefaultButton() doesn't apply because it only takes JButton as an input param. I wonder why it wasn't implemented to take AbstractButton. hmmm.

Selection in a combo when using Usebean??

          Hi All,
          In the JSP page, to select/display employeeType (Consulatant/Administrative Employee), i am having a combo box. I am using a UseBean tag and employeeType variable of the used bean, will have one of these values. How to show the selected employeeType?
          One way to acheive could be using "OPTION SELECTED TAG". Is there any better way to achieve this?
          Thanks,
          Amar


Use a JList for multiple selection.

Do I use JFrame or JDialog?

Hi,
I wanted to create a dialog which allows me to have two JTextArea's. In one list I list possible selection for the user. In the other text area, all the files the user selected will be in the text area. There will be two buttons for removal/addition of these items from the second text area. When you hit the OK button the owner of the dialog needs to grab that info.
Can an extension of a JDialog do this? Would it be suited for this? Or should I use an extension of a JFrame?
thanks for any help in advance,
Geoff

I would use a JList. The Swing tutorial on "How to Use Lists" gives an example of how to add/remove items from a single list. Changing this to work with two lists should be easy:
http://java.sun.com/docs/books/tutorial/uiswing/components/list.html#mutable

JList problems, can't write to a list

Hi there....can anyone help???
I'm having a problem with a dialog box...I use a dialog box to logon a new user (client) to my server, but the GUI on the client's side isn't showing who's online so to speak(I'm using a JList as my 'buddy' list type of window)....How do I get the dialog box to send the user's name to my client's GUI and add it to my who's online box??? Conversely how do I get the name to be removed when the user disconnects from the server??? Thanks everyone for any help you can provide....

You need to refresh the JList every time the data changes:
JList myjlist = new JList();
Vector data = new Vector(); //or use an array of type Object
//data changes
myjlist.setListData(data);

Using a JList

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