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Java Swing: how to stop unwanted shift-tab keystroke action

When I have a JTextField in a JPanel and it has focus, pressing "tab" doesn't do anything... but pressing "shift-tab" causes focus to be lost (FocusEvent.getOppositeComponent() is null).
If there are other focusable components on the JPanel (or rather under the "focus cycle root") this doesn't happen: instead, they get the focus on shift-tab.
In the SSCCE below I demonstrate this... each time you press Return in the search box you add a row to the JTable, which causes it to become focusable. You can also uncomment the line which makes the JRadioButtons unfocusable.
I looked at the InputMaps as well to see whether shift-tab is somehow involved there ... not at all.
I also tried experimenting with FocusTraversalPolicy to see whether I could understand the problem. No joy.
My goal: to stop "shift-tab" causing a loss of focus (focus disappears) when there is a single focusable component in the focus cycle root's ambit.
later
a workaround is to add the line
if( oppComp == null ){ impl.searchBox.requestFocus(); }
at the end of the focusLost method of the search box's FocusListener ... but for me this is only a workaround... 1) it doesn't solve the problem through understanding of the focus traversal mechanism; 2) there might be circs when you would need the focus to be lost from the search box...
import java.awt.*;
import java.awt.event.*;
import java.lang.*;
import java.lang.reflect.InvocationTargetException;
import java.util.*;
import javax.swing.*;
import javax.swing.table.*;
class BackTabProb {
JFrame mainFrame;
JTextField searchBox;
JTable resultsTable;
public static void print(String msg) {
System.out.println(msg);
}
public static void main(String[] a_args) throws InvocationTargetException, InterruptedException {
final BackTabProb impl = new BackTabProb();
class Show implements Runnable {
public void run() {
impl.mainFrame = new JFrame("Back Tab problem");
impl.mainFrame.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent windowEvent) {
impl.mainFrame.dispose();
}
});
impl.resultsTable = new JTable();
impl.resultsTable.setFocusable(false);
Vector<Object> dataVector = new Vector<Object>();
Vector<Object> colIdentifiers = new Vector<Object>(Arrays.asList(new String[] { "ONE", "TWO" }));
((DefaultTableModel) impl.resultsTable.getModel()).setDataVector(dataVector, colIdentifiers);
JScrollPane jsp = new JScrollPane(impl.resultsTable);
JPanel northPanel = new JPanel();
northPanel.setLayout(new BoxLayout(northPanel, BoxLayout.X_AXIS));
impl.searchBox = new JTextField("Enter search text", 10);
JLabel label = new JLabel("Search:");
label.setLabelFor(impl.searchBox);
northPanel.add(label);
northPanel.add(impl.searchBox);
ButtonGroup buttonGroup = new ButtonGroup();
ArrayList<JRadioButton> indexButtons = new ArrayList<JRadioButton>();
for (int i = 0; i < 2; i++) {
JRadioButton indexButton = new JRadioButton(i == 0 ? "Stemmer" : "Simple");
// commenting this out means back-tabbing from search box does not result
// in focus going "nowhere"
indexButton.setFocusable(false);
buttonGroup.add(indexButton);
northPanel.add(indexButton);
}
impl.mainFrame.getContentPane().setLayout(new BorderLayout());
impl.mainFrame.getContentPane().add(northPanel, BorderLayout.NORTH);
impl.mainFrame.getContentPane().add(jsp, BorderLayout.CENTER);
impl.mainFrame.pack();
impl.mainFrame.setVisible(true);
print("=== visible");
}
}
EventQueue.invokeAndWait(new Show());
class AddMore implements Runnable {
public void run() {
impl.mainFrame.setFocusTraversalPolicyProvider(true);
class SearchBoxFocusListener implements FocusListener {
public void focusGained(FocusEvent focusEvent) {
print("=== search box got focus");
impl.searchBox.selectAll();
}
public void focusLost(FocusEvent focusEvent) {
Component oppComp = focusEvent.getOppositeComponent();
print(String.format("=== search box lost focus to %s",
oppComp == null ? "nowhere" : oppComp.getClass()));
}
}
impl.searchBox.addFocusListener(new SearchBoxFocusListener());
class SearchBoxActionListener implements ActionListener {
public void actionPerformed( ActionEvent actionEvent ){
if( actionEvent.getSource() != null ){
((DefaultTableModel)impl.resultsTable.getModel()).insertRow( 0, new Object[]{ "blip", "blap" });
// as soon as the table has at least one row it is set to "focusable"
// commenting this out means back-tabbing from search box results
// in focus going "nowhere"
impl.resultsTable.setFocusable( true );
}
}
}
impl.searchBox.addActionListener( new SearchBoxActionListener() );
ActionMap am = impl.searchBox.getActionMap();
print("=== ActionMap");
for (Object key : am.allKeys()) {
print(String.format(" === action key %s", key));
}
for (int i = 0; i < 3; i++) {
print(String.format("=== InputMap type %d", i));
InputMap im = impl.searchBox.getInputMap(i);
KeyStroke[] allKeys = im.allKeys();
if (allKeys != null) {
for (KeyStroke ks : allKeys) {
print(String.format(" === keystroke %s object %s", ks, im.get(ks)));
}
}
}
// various experiments with FocusTraversalPolicy... NB LayoutTraversalPolicy
// is what the framework uses here by default
class MainFrameFocusTraversalPolicy extends LayoutTraversalPolicy {
public Component getComponentAfter(Container arg0, Component arg1) {
Component comp = super.getComponentAfter(arg0, arg1);
print(String.format("=== comp after %s", comp == null ? "Null" : comp.getClass()));
return comp;
}
public Component getComponentBefore(Container arg0, Component arg1) {
Component comp = super.getComponentBefore(arg0, arg1);
print(String.format("=== comp before %s", comp == null ? "Null" : comp.getClass()));
return comp;
}
public Component getDefaultComponent(Container arg0) {
Component comp = super.getDefaultComponent(arg0);
print(String.format("=== default comp %s", comp == null ? "Null" : comp.getClass()));
return comp;
}
public Component getFirstComponent(Container arg0) {
Component comp = super.getFirstComponent(arg0);
print(String.format("=== first comp %s", comp == null ? "Null" : comp.getClass()));
return comp;
// return impl.searchBox;
}
public Component getLastComponent(Container arg0) {
Component comp = super.getLastComponent(arg0);
print(String.format("=== last comp %s", comp == null ? "Null" : comp.getClass()));
return comp;
}
protected boolean accept(Component comp) {
boolean accept = super.accept(comp);
print(String.format("=== accept %s? %s", comp == null ? "Null" : comp.getClass(), accept));
return accept;
}
}
impl.mainFrame.setFocusTraversalPolicy(new MainFrameFocusTraversalPolicy());
}
}
EventQueue.invokeAndWait(new AddMore());
}
}

Maybe you can use Container#setFocusTraversalKeys(...) method:
Set<AWTKeyStroke> backwardKeys = Collections.emptySet();
//alone JTextField(pointed out by #mKorbel): impl.mainFrame.setFocusTraversalKeys(
impl.searchBox.setFocusTraversalKeys(
KeyboardFocusManager.BACKWARD_TRAVERSAL_KEYS, backwardKeys);

this still comes under the workaround heading for me... but it's a bit more useful than the workaround I gave under "later"
if( oppComp == null ){
final Component srcComp = (Component)focusEvent.getSource();
FocusTraversalPolicy ftp = impl.mainFrame.getFocusTraversalPolicy();
Component lastComp = ftp.getLastComponent( impl.mainFrame );
Component beforeComp = ftp.getComponentBefore( impl.mainFrame, srcComp );
if( lastComp == beforeComp ){
EventQueue.invokeLater( new Runnable(){
public void run() {
if( impl.mainFrame.isFocused()){
srcComp.requestFocus();
};
}});
}
}
Indeed, this is the situation faced by a single focusable component: on Shift-Tab the focus traversal policy then finds that the "before" comp is the same as the "last" comp. Under these circs component focus (as opposed to window focus) appears to vanish. The odd thing is that on Tab (traverse forwards), when the "after" comp is the same as the "first" comp, it doesn't. Is this a bug?
Anyway, having ascertained this you then have to check the focus of the window asynchronously... so that focus can be allowed to go to another window. Results in a slight flicker (boo!) on Shift-Tab.

Change background of JLabel in runtime using reflection

I need to change background of JLabels dynamically.
I've 70 JLabels in a class. All JLabels represent some specific items. The items names are same as the variable of JLabel. The Sold Items names are saved in database. If I run a query that will return an array of the sold items. The sold items that are same as the JLabel should change the background. Rest will not change.
I've got the variables of all fields like this:
Field fld[] = BlueLine.class.getDeclaredFields();
for (int i = 0; i < fld.length; i++)
{
System.out.println("Variable Name is : " + fld[i].getName());
}
How can I cast my fld to a JLabel and change background of the JLabel when certain condition meets ? for example:
if(fld[i] == label5){
label5.setBackground.(Color.red);
} // or something like this. ?
Any outline will help.

Currently you're just looking at the fields themselves - you're interested in the values of those fields. For example:
Object value = fld[i].get(target); // Or null for static fields
if (value == label5) {
...
}
Here target is a reference to the object whose fields you want to get the values from. For static fields, just use null, as per the comment.
It's not at all clear that all of this is a good idea, however - problems which can be solved with reflection are often better solved in a different way. We don't really have enough context to advise you of specifics at the moment, but I would recommend that you at least try to think of cleaner designs.

Try it using Jcomponent.putClientProperty() and Jcomponent.getClientProperty().
Steps to follow:
First set the name of the JLabel same as its variable name
Put it as client property of JPanel where JLabel is added
Get it back using client property from JPanel using name of JLabel
Note: you can access it by using Field.getName() as defined in your question.
Sample code :
final JFrame frame = new JFrame();
final JPanel panel = new JPanel();
panel.addContainerListener(new ContainerListener() {
#Override
public void componentRemoved(ContainerEvent e) {
String name = e.getChild().getName();
if (name != null) {
System.out.println(name + " removed");
panel.putClientProperty(name, null);
}
}
#Override
public void componentAdded(ContainerEvent e) {
String name = e.getChild().getName();
if (name != null) {
System.out.println(name + " added");
panel.putClientProperty(name, e.getChild());
}
}
});
MyLabels myLabels = new MyLabels();
panel.add(myLabels.getProduct1());
panel.add(myLabels.getProduct2());
panel.add(myLabels.getProduct3());
JButton btn = new JButton("Product1 and Product3 are sold");
btn.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
String[] soldItems = new String[] { "Product1", "Product3" };
for (String soldItem : soldItems) {
Object obj = panel.getClientProperty(soldItem);
if (obj instanceof JLabel) {
((JLabel) obj).setForeground(Color.RED);
}
}
}
});
panel.add(btn);
frame.add(panel);
frame.setSize(400, 200);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
MyLabels.java:
class MyLabels {
private JLabel Product1;
private JLabel Product2;
private JLabel Product3;
public MyLabels() {
Product1 = new JLabel("Product1");
Product1.setName(Product1.getText());
Product2 = new JLabel("Product2");
Product2.setName(Product2.getText());
Product3 = new JLabel("Product3");
Product3.setName(Product3.getText());
}
public JLabel getProduct1() {
return Product1;
}
public void setProduct1(JLabel product1) {
Product1 = product1;
}
public JLabel getProduct2() {
return Product2;
}
public void setProduct2(JLabel product2) {
Product2 = product2;
}
public JLabel getProduct3() {
return Product3;
}
public void setProduct3(JLabel product3) {
Product3 = product3;
}
}

Infinite focus loop on textFields

I have 2 JTextFields:
JTextField txtJobType, txtPriorityCode;
This is the functionality I need:
When user types in 'administration' in txtJobType and hits tab (or clicks away) an error check is done to see whether the field is empty or if the text entered exists in database. The way I have done that is:
private void txtJobTypeFocusLost(java.awt.event.FocusEvent evt) {
System.out.println("JobType Focus Lost");
if (!checkFieldExists(txtJobType.getText(), "jobType", "jobCode",
JobType.class) || txtJobType.getText().isEmpty()) {
txtJobType.requestFocusInWindow();
txtJobType.selectAll();
} else {
}
}
So if the field doesn't exist or the text is empty, then return focus to the txtJobType and highlight all the text (if any)
That works without a problem. However, I have the txtPriorityCode field which needs to have the exact same behaviour. So I did:
private void txtPriorityCodeFocusLost(java.awt.event.FocusEvent evt) {
System.out.println("PriorityCode Focus Lost");
if (!checkFieldExists(txtPriorityCode.getText(), "priority", "priorityCode",
Priority.class) || txtPriorityCode.getText().isEmpty()) {
txtPriorityCode.requestFocusInWindow();
txtPriorityCode.selectAll();
}
}
This is where the problem starts: if user leaves jobType and tabs to Priority then the code attempts to return focus back to jobtype, but because priority is also blank at that point, it will attempt to get focus back from jobtype, resulting in this output:
PriorityCode Focus Lost
JobType Focus Lost
PriorityCode Focus Lost
JobType Focus Lost
Any help on how I could implement this behaviour is appreciated, as I have to do this for at least 10 other textfields.
Thank You!

You shouldn't be fiddling with focus lost or other low-level constructs. Instead, why not simply use an InputVerifier as per this example and this one too?
For example, it could look something like this:
import javax.swing.*;
public class InputVerifierEg {
private JPanel mainPanel = new JPanel();
private JTextField txtJobType = new JTextField(10);
private JTextField txtPriorityCode = new JTextField(10);
public InputVerifierEg() {
txtJobType.setInputVerifier(new MyInputVerifier("jobType", "jobCode",
JobType.class));
txtPriorityCode.setInputVerifier(new MyInputVerifier("priority", "priorityCode",
Priority.class));
mainPanel.add(new JLabel("Job Type:"));
mainPanel.add(txtJobType);
mainPanel.add(Box.createHorizontalStrut(15));
mainPanel.add(new JLabel("Priority Code:"));
mainPanel.add(txtPriorityCode);
}
public JPanel getMainPanel() {
return mainPanel;
}
private static void createAndShowGui() {
JFrame frame = new JFrame("InputVerifierEg");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new InputVerifierEg().getMainPanel());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
class MyInputVerifier extends InputVerifier {
private String fieldName;
private String codeName;
private Class<?> classType;
public MyInputVerifier(String fieldName, String codeName, Class<?> classType) {
this.fieldName = fieldName;
this.codeName = codeName;
this.classType = classType;
}
#Override
public boolean verify(JComponent input) {
JTextField tField = (JTextField) input;
// assuming that the checkFieldExists is a static method of a utility class
if (!FieldCheckerUtil.checkFieldExists(tField.getText(), fieldName,
codeName, classType)) {
return false;
}
if (tField.getText().trim().isEmpty()) {
return false;
}
return true;
}
#Override
public boolean shouldYieldFocus(JComponent input) {
JTextField tField = (JTextField) input;
if (verify(input)) {
return true;
} else {
tField.selectAll();
// show JOptionPane error message?
return false;
}
}
}

Personally, I hate it when validation is done like this and prevents me from moving around fields in a form as I see fit. Why not do validation on all the fields when the form is submitted and highlight the invalid ones at that time?

Maybe do one check of:
txtPriorityCode.getText().isEmpty()
And then on the other, test if:
!txtPriorityCode.getText().isEmpty() && txtJobType.getText().isEmpty()
i.e. only do the check on the second one if the first one isn't empty.

Setting component focus in JOptionPane.showOptionDialog()

In order to have custom button captions in an input dialog, I created the following code:
String key = null;
JTextField txtKey = new JTextField();
int answerKey = JOptionPane.showOptionDialog(this, new Object[] {pleaseEnterTheKey, txtKey}, decryptionKey, JOptionPane.OK_CANCEL_OPTION, JOptionPane.QUESTION_MESSAGE, null, new Object[] {okCaption, cancelCaption}, okCaption);
if (answerKey == JOptionPane.OK_OPTION && txtKey.getText() != null) {
key = txtKey.getText();
}
How can I move the focus (cursor) to the text field as the dialog is displayed?
UPDATE
This does not work for me, I mean the textfield has no focus:
OS: Fedora - Gnome
public class Test {
public static void main(String[] args) {
String key = null;
JTextField txtKey = new JTextField();
txtKey.addAncestorListener(new RequestFocusListener());
int answerKey = JOptionPane.showOptionDialog(null, new Object[]{"Please enter the key:", txtKey}, "Title", JOptionPane.OK_CANCEL_OPTION, JOptionPane.QUESTION_MESSAGE, null, new Object[]{"OKKK", "CANCELLLL"}, "OKKK");
if (answerKey == JOptionPane.OK_OPTION && txtKey.getText() != null) {
key = txtKey.getText();
}
}
}

Dialog Focus shows how you can easily set the focus on any component in a modal dialog.

public static String getPassword(String title) {
JPanel panel = new JPanel();
final JPasswordField passwordField = new JPasswordField(10);
panel.add(new JLabel("Password"));
panel.add(passwordField);
JOptionPane pane = new JOptionPane(panel, JOptionPane.QUESTION_MESSAGE, JOptionPane.OK_CANCEL_OPTION) {
#Override
public void selectInitialValue() {
passwordField.requestFocusInWindow();
}
};
pane.createDialog(null, title).setVisible(true);
return passwordField.getPassword().length == 0 ? null : new String(passwordField.getPassword());
}

passing null as the last argument is the solution. At least it worked for me.
String key = null;
JTextField txtKey = new JTextField();
int answerKey = JOptionPane.showOptionDialog(this, new Object[] {pleaseEnterTheKey, txtKey}, decryptionKey, JOptionPane.OK_CANCEL_OPTION, JOptionPane.QUESTION_MESSAGE, null, new Object[] {okCaption, cancelCaption}, null);
if (answerKey == JOptionPane.OK_OPTION && txtKey.getText() != null) {
key = txtKey.getText();
}
But even this solution bring another problem:
Focused component and Default component are different. Default component or default button is the button which its onclick fires if you press ENTER KEY.The last argument define the default component which gets the focus too and passing null brings the problem of having no default component!
I solved it for my code this way but I guess it is not a best practice:
String key = null;
final JTextField txtKey = new JTextField();
txtKey.addKeyListener(new KeyAdapter() {
#Override
public void keyPressed(KeyEvent e) {
int keyCode = e.getKeyCode();
if (keyCode == 10) { //enter key
Container parent = txtKey.getParent();
while (!(parent instanceof JOptionPane)) {
parent = parent.getParent();
}
JOptionPane pane = (JOptionPane) parent;
final JPanel pnlBottom = (JPanel) pane.getComponent(pane.getComponentCount() - 1);
for (int i = 0; i < pnlBottom.getComponents().length; i++) {
Component component = pnlBottom.getComponents()[i];
if (component instanceof JButton) {
final JButton okButton = ((JButton)component);
if (okButton.getText().equalsIgnoreCase(okCaption)) {
ActionListener[] actionListeners = okButton.getActionListeners();
if (actionListeners.length > 0) {
actionListeners[0].actionPerformed(null);
}
}
}
}
}
}
});

I had the same problem with the RequestFocusListener() not working on Linux, after following the discussion on http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=5018574 I found that adding an invokeLater fixed it for now...
public class RequestFocusListener implements AncestorListener
{
public void ancestorAdded(final AncestorEvent e)
{
final AncestorListener al= this;
SwingUtilities.invokeLater(new Runnable(){
#Override
public void run() {
JComponent component = (JComponent)e.getComponent();
component.requestFocusInWindow();
component.removeAncestorListener( al );
}
});
}
public void ancestorMoved(AncestorEvent e) {}
public void ancestorRemoved(AncestorEvent e) {}
}

The trick is to (a) use an AncestorListener on the text component to request focus, and when the focus is lost again (given to the default button), ask for focus a second time using a FocusListener on the text component (but don't keep asking for focus after that):
final JPasswordField accessPassword = new JPasswordField();
accessPassword.addAncestorListener( new AncestorListener()
{
#Override
public void ancestorRemoved( final AncestorEvent event )
{
}
#Override
public void ancestorMoved( final AncestorEvent event )
{
}
#Override
public void ancestorAdded( final AncestorEvent event )
{
// Ask for focus (we'll lose it again)
accessPassword.requestFocusInWindow();
}
} );
accessPassword.addFocusListener( new FocusListener()
{
#Override
public void focusGained( final FocusEvent e )
{
}
#Override
public void focusLost( final FocusEvent e )
{
if( isFirstTime )
{
// When we lose focus, ask for it back but only once
accessPassword.requestFocusInWindow();
isFirstTime = false;
}
}
private boolean isFirstTime = true;
} );

Better way to do it: create the JOptionPane using the constructor, override selectInitialValue to set the focus, and then build the dialog using createDialog.
// Replace by the constructor you want
JOptionPane pane = new JOptionPane(panel, JOptionPane.PLAIN_MESSAGE, JOptionPane.OK_CANCEL_OPTION) {
#Override
public void selectInitialValue() {
textArea.requestFocusInWindow();
}
};
JDialog dialog = pane.createDialog(owner, title);
dialog.setVisible(true);

Try this
String key = null;
JTextField txtKey = new JTextField();
Object[] foo = {pleaseEnterTheKey, txtKey};
int answerKey = JOptionPane.showOptionDialog(this, foo, decryptionKey, JOptionPane.OK_CANCEL_OPTION, JOptionPane.QUESTION_MESSAGE, null, new Object[] {okCaption, cancelCaption}, foo[1]);
if (answerKey == JOptionPane.OK_OPTION && txtKey.getText() != null) {
key = txtKey.getText();
}

I found a solution !
Very primitive, but works.
Just jump to the field by java.awt.Robot using key "Tab".
I've created utils method calls "pressTab(..)"
For example:
GuiUtils.pressTab(1); <------------- // add this method before popup show
int result = JOptionPane.showConfirmDialog(this, inputs, "Text search window", JOptionPane.PLAIN_MESSAGE);
if (result == JOptionPane.OK_OPTION)
{
}
If you should press multiple times on "Tab" to get your Component you can use below method:
GUIUtils.pressTab(3);
Definition:
public static void pressTab(int amountOfClickes)
{
SwingUtilities.invokeLater(new Runnable()
{
public void run()
{
try
{
Robot robot = new Robot();
int i = amountOfClickes;
while (i-- > 0)
{
robot.keyPress(KeyEvent.VK_TAB);
robot.delay(100);
robot.keyRelease(KeyEvent.VK_TAB);
}
}
catch (AWTException e)
{
System.out.println("Failed to use Robot, got exception: " + e.getMessage());
}
}
});
}
If your Component location is dynamic, you can run over the while loop without limitation, but add some focus listener on the component, to stop the loop once arrived to it.

How would I go about highlighting an item in a JList? [duplicate]

I am trying to change JList rows dynamically. I need change nth row colour, highlight it(n is unknown during compilation). I saw a lot of examples with custom ListCellRenderer, but all were "static".
In other words I have JList with x rows. During runtime my "business logic" detects nth row is important. So I want make its background green, wait one second, and then make it white again. One more thing, don't wan change row selection.
What is the best way to do so?

Simple, set a custom ListCellRenderer to your JList using:
list.setCellRenderer(myListCellrenderer);
Now inside the overridden method getListCellRendererComponent() do something like this:
public Component getListCellRendererComponent(.....) {
Component c = super.getListCellRendererComponent();
c.setBackGround(Color.blue)
return c;
}
The above example assumed that your custom renderer overrid DefaultListCellRenderer

Based on ListDemo sample from SUN.
If you enter some text in the textfield which isn't in the list and you hit highlight it gets added.
If the text is in the list and you hit highlight the entry in the list gets temporarily highlighted blue.
Note the solution here with the match field is just for demo. For more correct implementation consider the other ideas proposed and consider using javax.swing.Timer
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
public class ListDemo extends JPanel {
private JList list;
private DefaultListModel listModel;
public String match = null;
private static final String hireString = "Highlight";
private JTextField employeeName;
public ListDemo() {
super(new BorderLayout());
listModel = new DefaultListModel();
listModel.addElement("Test1");
listModel.addElement("Test2");
listModel.addElement("Test3");
list = new JList(listModel);
list.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
list.setSelectedIndex(0);
list.setVisibleRowCount(5);
list.setCellRenderer(new MyListCellRenderer());
JScrollPane listScrollPane = new JScrollPane(list);
JButton hireButton = new JButton(hireString);
HireListener hireListener = new HireListener(hireButton);
hireButton.setActionCommand(hireString);
hireButton.addActionListener(hireListener);
hireButton.setEnabled(false);
employeeName = new JTextField(10);
employeeName.addActionListener(hireListener);
employeeName.getDocument().addDocumentListener(hireListener);
listModel.getElementAt(list.getSelectedIndex()).toString();
JPanel buttonPane = new JPanel();
buttonPane.setLayout(new BoxLayout(buttonPane,
BoxLayout.LINE_AXIS));
buttonPane.add(Box.createHorizontalStrut(5));
buttonPane.add(employeeName);
buttonPane.add(hireButton);
buttonPane.setBorder(BorderFactory.createEmptyBorder(5,5,5,5));
add(listScrollPane, BorderLayout.CENTER);
add(buttonPane, BorderLayout.PAGE_END);
}
class MyListCellRenderer extends JLabel implements ListCellRenderer {
public MyListCellRenderer() {
setOpaque(true);
}
public Component getListCellRendererComponent(JList paramlist, Object value, int index, boolean isSelected, boolean cellHasFocus) {
setText(value.toString());
if (value.toString().equals(match)) {
setBackground(Color.BLUE);
SwingWorker worker = new SwingWorker() {
#Override
public Object doInBackground() {
try {
Thread.sleep(5000);
} catch (InterruptedException e) { /*Who cares*/ }
return null;
}
#Override
public void done() {
match = null;
list.repaint();
}
};
worker.execute();
} else
setBackground(Color.RED);
return this;
}
}
class HireListener implements ActionListener, DocumentListener {
private boolean alreadyEnabled = false;
private JButton button;
public HireListener(JButton button) {
this.button = button;
}
public void actionPerformed(ActionEvent e) {
String name = employeeName.getText();
if (listModel.contains(name)) {
match = name;
list.repaint();
employeeName.requestFocusInWindow();
employeeName.selectAll();
return;
}
if (name.equals("")) {
Toolkit.getDefaultToolkit().beep();
employeeName.requestFocusInWindow();
employeeName.selectAll();
return;
}
int index = list.getSelectedIndex();
if (index == -1)
index = 0;
else
index++;
listModel.insertElementAt(employeeName.getText(), index);
employeeName.requestFocusInWindow();
employeeName.setText("");
list.setSelectedIndex(index);
list.ensureIndexIsVisible(index);
}
public void insertUpdate(DocumentEvent e) {
enableButton();
}
public void removeUpdate(DocumentEvent e) {
handleEmptyTextField(e);
}
public void changedUpdate(DocumentEvent e) {
if (!handleEmptyTextField(e))
enableButton();
}
private void enableButton() {
if (!alreadyEnabled)
button.setEnabled(true);
}
private boolean handleEmptyTextField(DocumentEvent e) {
if (e.getDocument().getLength() <= 0) {
button.setEnabled(false);
alreadyEnabled = false;
return true;
}
return false;
}
}
private static void createAndShowGUI() {
JFrame frame = new JFrame("ListDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JComponent newContentPane = new ListDemo();
newContentPane.setOpaque(true);
frame.setContentPane(newContentPane);
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() { createAndShowGUI(); }
});
}
}

Your custom ListCellRenderer, which implements the method getListCellRendererComponent, will have access to both the JList and the value that it is redering. This gives you a couple options for how to determine when to paint the nth row green:
You could subclass JList and have the renderer ask it which color to use for the bg. The JList subclass could trigger a repaint when the business logic determines that it is time for the nth row to be green, and then start an Swing Timer to trigger a repaint returning the bg back to normal
When the business logic determines when you should show the row as green, you also have the option of setting state on the backing object of the row, and test it for that state within getListCellRendererComponent, setting the bg green if the state is correct. Again, you have the option of setting an Swing Timer to revert the state on the backing object.