Develop Reference

Java Focus Traversal Policy

I need help implementing my own traversal policy.
My goal was to be able to traverse with tab some of the components in a panel, not all of them.
I was able to research the FocusTraversalPolicy class and figure out a little how this works. The code below shows how far I got. But I seem to have hit a wall.
This code will allow me to traverse from one component to another, but there are in my Container smaller jpanels with jtextfields in them. For some reason, I am not able to traverse to these using tab, even though I added the jpanels into my policy.
I am aware that I can just access the textfields inside these jpanels and add them to my policy. However, since these smaller jpanels are sort of dynamic and can add extra components inside of them, I am looking more for something that will allow me to pass from the Parent container traversal cycle to the smaller one.
I could be wrong, but I believe I should add something to the getComponentAfter(...) and the getComponentBefore(...) methods. As you can see, I commented out some of the things I was trying. I would appreciate any help you can give me. I attached a picture of my panel so you can see what I mean.
public class TabFocusAdapter extends FocusTraversalPolicy implements FocusListener, MouseListener {
private ArrayList<Component> comps = new ArrayList<Component>();
private int focus, def;
private boolean mouse_focus = false;
public TabFocusAdapter(int f) {
focus = def = f;
}
#Override
/***Returns the component after the current one
* if current one is the last in the cycle, it will return the first
* it will skip all disabled components */
public Component getComponentAfter(Container aContainer, Component aComponent) {
//if(((Container) aComponent).getFocusTraversalPolicy()!=null)
//if(aComponent)
//return ((Container)aComponent).getFocusTraversalPolicy().getFirstComponent((Container) aComponent);
focus++;
if(focus == comps.size()) focus = 0;
Component comp = comps.get(focus);
while(!comp.isEnabled() || !comp.isShowing() || !comp.isVisible()) {
focus++;
if(focus == comps.size()) focus = 0;
comp = comps.get(focus);
}
return comps.get(focus);
}
#Override
/**Returns the component before the current one
* if current one is the first in the cycle, it will return the last
* it will skip all disabled components */
public Component getComponentBefore(Container aContainer, Component aComponent) {
focus--;
if(focus == -1) focus = comps.size()-1;
Component comp = comps.get(focus);
while(!comp.isEnabled() || !comp.isShowing() || !comp.isVisible()) {
focus--;
if(focus == -1) focus = comps.size()-1;
comp = comps.get(focus);
}
return comps.get(focus);
}
#Override
public Component getFirstComponent(Container aContainer) {
return comps.get(0);
}
#Override
public Component getLastComponent(Container aContainer) {
return comps.get(comps.size() - 1);
}
#Override
/**Returns the starting component */
public Component getDefaultComponent(Container aContainer) {
return comps.get(def);
}
public void addComp(Component comp) {
comps.add(comp);
comp.addMouseListener(this);
comp.addFocusListener(this);
}
#Override
public void focusGained(FocusEvent e) {
Component comp = e.getComponent();
if(!mouse_focus && comp instanceof JTextComponent)
((JTextComponent)comp).selectAll();
}
#Override
public void mousePressed(MouseEvent e) {
mouse_focus = true;
focus = comps.indexOf(e.getComponent());
}
#Override
public void mouseReleased(MouseEvent e) {
mouse_focus = false;
}
#Override
public void mouseClicked(MouseEvent e) {}
#Override
public void focusLost(FocusEvent e) {}
#Override
public void mouseEntered(MouseEvent e) {}
#Override
public void mouseExited(MouseEvent e) {}
}

I solved my problem by including a series of checks into the getComponentAfter(...) and getComponentBefore(...) methods. I am including my code below.
Basically, to determine whether to move to a lower cycle, it asks whether the next component is a Focus Cycle Root.
When concluding a cycle, to determine whether to move to an upper cycle, it asks whether the parent of the container is a Focus Traversal Policy Provider.
I got the general idea for this solution by looking at how these methods where implemented by the default traversal policies of my JFrame.
'''
public Component getComponentAfter(Container aContainer, Component aComponent) {
Component comp;
do{
focus++;
if(focus == comps.size()) {
focus = 0;
ancestor = aContainer;
do ancestor = ancestor.getParent();
while(ancestor!=null && !ancestor.isFocusTraversalPolicyProvider());
if(ancestor != null && ancestor.isFocusTraversalPolicyProvider())
return (ancestor
.getFocusTraversalPolicy()
.getComponentAfter(ancestor, aContainer));
}
comp = comps.get(focus);
} while(!comp.isEnabled() || !comp.isShowing() || !comp.isVisible());
if(comp instanceof Container && ((Container)comp).isFocusCycleRoot()) {
return ((Container)comp)
.getFocusTraversalPolicy()
.getDefaultComponent((Container) comp);
}
return comp;
}
'''

Override method that toggles 'isSelected' in getListCellRendererComponent

I would like to make my own method that controles when a component is 'isSelected'.
I have a JList containing multiple JPanel. The constructing class of the JPanel extends ListCellRenderer<>.
To show that one of the JList-component (the JPanels) is selected i use;
#Override
public Component getListCellRendererComponent(..., boolean isSelected, ...) {
if(isSelected){
setBackground(list.getSelectionBackground());
setForeground(list.getSelectionForeground());
} else {
setBackground(list.getBackground());
setForeground(list.getForeground());
}
return this;
}
I would like a method that keeps a selected item 'selected' eventhough I choose to select another. I understand this can be done by holding down CTRL, but .setSelectionMode(ListSelectionModel.MULTIPLE_INTERVAL_SELECTION); does not quite do the trick. I would rather like to select multiple by clicking on them, and deselect by clicking on them.
For this i have worked with the ListSelectionMode, but i cant find a way.
When done the above I would like to implement a method that only selects a component in the list when clicked in a certain area (instead of the whole component which is preset). I have made this method, which returns true if the correct area is clicked, else false. But since I cant figure out how to override the mouseevent that makes the components 'isSelected' this has been tricky.
Here is the code for the method I would like to override the 'isSelected' method;
this.addMouseListener(new MouseAdapter() {
#Override
public void mousePressed(MouseEvent evt) {
if(ActionHandler.mouseClickedPrebuild(evt.getPoint())){
//This code runs if that special place is clicked!
//So now the component should be 'isSelected' or
//deselected if it already was 'isSelected'.
}
}
});
This code is in the constructor of my JList
And the mouseClickedPrebuild method;
public static boolean mouseClickedPrebuild(Point point) {
int index = theJList.locationToIndex(point);
Rectangle bounds = theJList.getCellBounds(index,index);
Point p = bounds.getLocation();
return ( ... long list of greater than & less than ...);
//This gives the certain area which is accepted to return true

I solved the issue!
So I get my view showing by running this line;
// UI Class JScrollPane Custom JList
UIConstructor.listview.setViewportView(new ListView( -insert ArrayList here- ));
Here is my ListView. The custom DefaultListSelectionModel I used to solve my problem was posted by #FuryComptuers right here;
JList - deselect when clicking an already selected item
I had to make a few changes to the code, since the two methods in the selectionModel will run before my mouseevent. I saved the variabels staticly, so instead of running the code in setSelectionInterval I did it inside my mousePressed.
I then could add the boolean isSelected which returns true, if a curtain area within a specific list element is clicked.
public class ListViewd extends JList {
static boolean isSelected;
static Point point;
static boolean gS = false;
static int in0;
static int in1;
#Override
public Dimension getPreferredScrollableViewportSize() {
Dimension size = super.getPreferredScrollableViewportSize();
size.setSize(new Dimension(0,0));
return size;
}
public ListView(ArrayList<System> items) {
DefaultListModel<System> list = new DefaultListModel<System>();
for (System item : items) {
list.addElement(item);
}
this.setSelectionModel(new DefaultListSelectionModel() {
boolean gestureStarted = false;
#Override
public void setSelectionInterval(int index0, int index1) {
gS = gestureStarted;
in0 = index0;
in1 = index1;
gestureStarted = true;
}
#Override
public void setValueIsAdjusting(boolean isAdjusting) {
if (!isAdjusting) {
gestureStarted = false;
}
}
});
ListSelectionModel selectionModel = this.getSelectionModel();
addMouseListener(new MouseAdapter() {
#Override
public void mousePressed(MouseEvent e) {
point = e.getPoint();
isSelected = ActionHandler.mouseClickedPrebuild(point);
if(!gS && isSelected){
if (isSelectedIndex(in0)) {
selectionModel.removeSelectionInterval(in0, in1);
} else {
selectionModel.addSelectionInterval(in0, in1);
}
}
}
});
setModel(list);
setCellRenderer(new ListModelPrebuild());
}

How to keep the popup menu of a JComboBox open on populating it?

I have a JComboBox on my Panel. One of the popup menu items is 'More' and when I click that I fetch more menu items and add them to the existing list. After this, I wish to keep the popup menu open so that the user realizes that more items have been fetched however, the popup closes. The event handler code I am using is as follows
public void actionPerformed(ActionEvent e)
{
if (e.getSource() == myCombo) {
JComboBox selectedBox = (JComboBox) e.getSource();
String item = (String) selectedBox.getSelectedItem();
if (item.toLowerCase().equals("more")) {
fetchItems(selectedBox);
}
selectedBox.showPopup();
selectedBox.setPopupVisible(true);
}
}
private void fetchItems(JComboBox box)
{
box.removeAllItems();
/* code to fetch items and store them in the Set<String> items */
for (String s : items) {
box.addItem(s);
}
}
I do not understand why the showPopup() and setPopupVisible() methods are not functioning as expected.

add the following line in the fetchItems method
SwingUtilities.invokeLater(new Runnable(){
public void run()
{
box.showPopup();
}
}
If u call selectedBox.showPopup(); inside invokelater also it will work.

overwrite the JCombobox setPopupVisible metod
public void setPopupVisible(boolean v) {
if(v)
super.setPopupVisible(v);
}

jComboBox1 = new javax.swing.JComboBox(){
#Override
public void setPopupVisible(boolean v) {
super.setPopupVisible(true); //To change body of generated methods, choose Tools | Templates.
}
};

I found some simple solution to always keep popup open. It may be useful with some custom JComboBox'es, like the one I have in my project, but is a little hacky.
public class MyComboBox extends JComboBox
{
boolean keep_open_flag = false; //when that flag ==true, popup will stay open
public MyComboBox(){
keep_open_flag = true; //set that flag where you need
setRenderer(new MyComboBoxRenderer()); //our spesial render
}
class MyComboBoxRenderer extends BasicComboBoxRenderer {
public Component getListCellRendererComponent(JList list, Object value,
int index, boolean isSelected, boolean cellHasFocus) {
if (index == -1){ //if popup hidden
if (keep_open_flag) showPopup(); //show it again
}
}
}
}

Right-click context menu for Java JTree?

I'm trying to implement pop-up menus in Java JTree. I've sub-classed DefaultTreeCellRenderer (to change node appearance) and DefaultTreeCellEditor (to create Components to attach event listeners to, since apparently the Components that DefaultTreeCellRenderer.getTreeCellRendererComponent() returns can't do it?). I don't really want to "edit" the nodes, just be able to pop-up a menu when a node gets right-clicked, but this is the only way I can think of doing it right now...
Below is the code that I have so far-- I'm just trying to figure out how to capture MouseEvents. It sort of works, but badly. What's a better way to accomplish what I'm trying to do here?
private class My_TreeCellRenderer extends DefaultTreeCellRenderer {
My_TreeCellRenderer() {
super ();
}
public Component getTreeCellRendererComponent(JTree tree, Object value, boolean selected, boolean expanded, boolean leaf, int row, boolean hasFocus) {
super.getTreeCellRendererComponent(tree, value, selected, expanded, leaf, row, hasFocus);
// set label text and tool tips
setText(((My_Object)value).getTreeLabel());
setToolTipText(((My_Object)value).getTreeToolTip());
return this;
}
}
private class My_TreeCellEditor extends DefaultTreeCellEditor {
private MouseAdapter ma;
My_TreeCellEditor(JTree tree, DefaultTreeCellRenderer renderer) {
super (tree, renderer);
ma = new MouseAdapter() {
public void mousePressed(MouseEvent e) {
if (e.isPopupTrigger()) {
System.out.println("My Popup");
}
}
public void mouseReleased(MouseEvent e) {
if (e.isPopupTrigger()) {
System.out.println("My Popup");
}
}
};
}
public Component getTreeCellEditorComponent(JTree tree, Object value, boolean selected, boolean expanded, boolean leaf, int row) {
String src_filename = null;
// return non-editing component
Component c = renderer.getTreeCellRendererComponent(tree, value, selected, expanded, leaf, row, true);
// add mouse listener if it's not listening already
MouseListener mouseListeners[] = c.getMouseListeners();
int i;
for (i=0; i < mouseListeners.length && mouseListeners[i] != ma; i++);
if (i >= mouseListeners.length)
c.addMouseListener(ma);
return c;
}
protected boolean canEditImmediately(EventObject event) {
if (event instanceof MouseEvent && ((MouseEvent)event).getClickCount() == 1)
return true;
else
return false;
}
}

This task is simple to accomplish, the following is all you need:
//create a class which implements the MouseListener interface and
//implement the following in your overridden mouseClicked method
#Override
public void mouseClicked(MouseEvent e) {
if (SwingUtilities.isRightMouseButton(e)) {
int row = tree.getClosestRowForLocation(e.getX(), e.getY());
tree.setSelectionRow(row);
popupMenu.show(e.getComponent(), e.getX(), e.getY());
}
}
You can then add this custom listener to your desired tree(s).

Taken right out of the JTree API
// If you are interested in detecting either double-click events or when a user clicks on a node, regardless of whether or not it was selected, we recommend you do the following:
final JTree tree = ...;
MouseListener ml = new MouseAdapter() {
public void mousePressed(MouseEvent e) {
int selRow = tree.getRowForLocation(e.getX(), e.getY());
TreePath selPath = tree.getPathForLocation(e.getX(), e.getY());
if(selRow != -1) {
if(e.getClickCount() == 1) {
mySingleClick(selRow, selPath);
}
else if(e.getClickCount() == 2) {
myDoubleClick(selRow, selPath);
}
}
}
};
tree.addMouseListener(ml);
Of course you need to modify it a bit for right click instead of left click

Thanks everyone. I knew something was wrong when I was spending that much effort on implementing a simple popup.
I dismissed this line of thought at first because it felt weird to resort to x- and y- coordinates to find the node I'm looking for, but I guess this is the way to do it.
// add MouseListener to tree
MouseAdapter ma = new MouseAdapter() {
private void myPopupEvent(MouseEvent e) {
int x = e.getX();
int y = e.getY();
JTree tree = (JTree)e.getSource();
TreePath path = tree.getPathForLocation(x, y);
if (path == null)
return;
tree.setSelectionPath(path);
My_Obj obj = (My_Obj)path.getLastPathComponent();
String label = "popup: " + obj.getTreeLabel();
JPopupMenu popup = new JPopupMenu();
popup.add(new JMenuItem(label));
popup.show(tree, x, y);
}
public void mousePressed(MouseEvent e) {
if (e.isPopupTrigger()) myPopupEvent(e);
}
public void mouseReleased(MouseEvent e) {
if (e.isPopupTrigger()) myPopupEvent(e);
}
};
(...)
JTree tree = new JTree();
tree.addMouseListener(ma);

I think you're making things way harder than they need to be.
JTree has several "add_foo_Listener" methods on it. Implement one of those (TreeSelectionListener looks about right), and then you've got the currently selected node.
Implement a MouseListener so that you can detect the right-click event (and add it to the JTree, since JTree's a Component), and then you should have everything you need to post a context-sensitive menu.
Check out this tutorial for more details.

The Renderer is only a transient "rubber stamp", so adding an input listener on that wont be particularly helpful. The Editor, as you point out, is only there once you have gestured to edit. So you want to add a listener to the JTree (assuming it isn't implemented as a composite component).

Call addRightClickListener() to add the right-click context menu listener to your JTree. Both overrides are for proper cross-platform functionality (Windows and Linux differ here).
private void addRightClickListener()
{
MouseListener mouseListener = new MouseAdapter()
{
#Override
public void mousePressed(MouseEvent mouseEvent)
{
handleContextMenu(mouseEvent);
}
#Override
public void mouseReleased(MouseEvent mouseEvent)
{
handleContextMenu(mouseEvent);
}
};
tree.addMouseListener(mouseListener);
}
private void handleContextMenu(MouseEvent mouseEvent)
{
if (mouseEvent.isPopupTrigger())
{
MyContextMenu contextMenu = new MyContextMenu();
contextMenu.show(mouseEvent.getComponent(),
mouseEvent.getX(),
mouseEvent.getY());
}
}

How do I make a list with checkboxes in Java Swing?

What would be the best way to have a list of items with a checkbox each in Java Swing?
I.e. a JList with items that have some text and a checkbox each?

A wonderful answer is this CheckBoxList. It implements Telcontar's answer (though 3 years before :)... I'm using it in Java 1.6 with no problems. I've also added an addCheckbox method like this (surely could be shorter, haven't used Java in a while):
public void addCheckbox(JCheckBox checkBox) {
ListModel currentList = this.getModel();
JCheckBox[] newList = new JCheckBox[currentList.getSize() + 1];
for (int i = 0; i < currentList.getSize(); i++) {
newList[i] = (JCheckBox) currentList.getElementAt(i);
}
newList[newList.length - 1] = checkBox;
setListData(newList);
}
I tried out the demo for the Jidesoft stuff, playing with the CheckBoxList I encountered some problems (behaviors that didn't work). I'll modify this answer if I find problems with the CheckBoxList I linked to.

Create a custom ListCellRenderer and asign it to the JList.
This custom ListCellRenderer must return a JCheckbox in the implementantion of getListCellRendererComponent(...) method.
But this JCheckbox will not be editable, is a simple paint in the screen is up to you to choose when this JCheckbox must be 'ticked' or not,
For example, show it ticked when the row is selected (parameter isSelected), but this way the check status will no be mantained if the selection changes. Its better to show it checked consulting the data below the ListModel, but then is up to you to implement the method who changes the check status of the data, and notify the change to the JList to be repainted.
I Will post sample code later if you need it
ListCellRenderer

Just implement a ListCellRenderer
public class CheckboxListCellRenderer extends JCheckBox implements ListCellRenderer {
public Component getListCellRendererComponent(JList list, Object value, int index,
boolean isSelected, boolean cellHasFocus) {
setComponentOrientation(list.getComponentOrientation());
setFont(list.getFont());
setBackground(list.getBackground());
setForeground(list.getForeground());
setSelected(isSelected);
setEnabled(list.isEnabled());
setText(value == null ? "" : value.toString());
return this;
}
}
and set the renderer
JList list = new JList();
list.setCellRenderer(new CheckboxListCellRenderer());
this will result in
Details at Custom swing component renderers.
PS: If you want radio elements just replace extends JCheckbox with extends JRadioButton.

I'd probably be looking to use a JTable rather than a JList and since the default rendering of a checkbox is rather ugly, I'd probably be looking to drop in a custom TableModel, CellRenderer and CellEditor to represent a boolean value. Of course, I would imagine this has been done a bajillion times already. Sun has good examples.

Better solution for Java 7 and newer
I stumbled upon this question and realized that some of the answers are pretty old and outdated. Nowadays, JList is generic and thus there are better solutions.
My solution of the generic JCheckBoxList:
import java.awt.Component;
import javax.swing.*;
import javax.swing.border.*;
import java.awt.event.*;
#SuppressWarnings("serial")
public class JCheckBoxList extends JList<JCheckBox> {
protected static Border noFocusBorder = new EmptyBorder(1, 1, 1, 1);
public JCheckBoxList() {
setCellRenderer(new CellRenderer());
addMouseListener(new MouseAdapter() {
public void mousePressed(MouseEvent e) {
int index = locationToIndex(e.getPoint());
if (index != -1) {
JCheckBox checkbox = (JCheckBox) getModel().getElementAt(index);
checkbox.setSelected(!checkbox.isSelected());
repaint();
}
}
});
setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
}
public JCheckBoxList(ListModel<JCheckBox> model){
this();
setModel(model);
}
protected class CellRenderer implements ListCellRenderer<JCheckBox> {
public Component getListCellRendererComponent(
JList<? extends JCheckBox> list, JCheckBox value, int index,
boolean isSelected, boolean cellHasFocus) {
JCheckBox checkbox = value;
//Drawing checkbox, change the appearance here
checkbox.setBackground(isSelected ? getSelectionBackground()
: getBackground());
checkbox.setForeground(isSelected ? getSelectionForeground()
: getForeground());
checkbox.setEnabled(isEnabled());
checkbox.setFont(getFont());
checkbox.setFocusPainted(false);
checkbox.setBorderPainted(true);
checkbox.setBorder(isSelected ? UIManager
.getBorder("List.focusCellHighlightBorder") : noFocusBorder);
return checkbox;
}
}
}
For dynamically adding JCheckBox lists you need to create your own ListModel or add the DefaultListModel.
DefaultListModel<JCheckBox> model = new DefaultListModel<JCheckBox>();
JCheckBoxList checkBoxList = new JCheckBoxList(model);
The DefaultListModel are generic and thus you can use methods specified by JAVA 7 API here like this:
model.addElement(new JCheckBox("Checkbox1"));
model.addElement(new JCheckBox("Checkbox2"));
model.addElement(new JCheckBox("Checkbox3"));

I recommend you use a JPanel with a GridLayout of 1 column. Add the checkBoxes to the JPanel, and set the JPanel as the data source of a JScrollPane. And to get the selected CheckBoxes, just call the getComponents() of the JPanel to get the CheckBoxes.

Odds are good w/ Java that someone has already implemented the widget or utility you need. Part of the benefits of a large OSS community. No need to reinvent the wheel unless you really want to do it yourself. In this case it would be a good learning exercise in CellRenderers and Editors.
My project has had great success with JIDE. The component you want, a Check Box List, is in the JIDE Common Layer (which is OSS and hosted on java.net). The commercial stuff is good too, but you don't need it.
http://www.jidesoft.com/products/oss.htm
https://jide-oss.dev.java.net/

I don't like the solutions that put a Checkbox into the model. The model should only contain data not display elements.
I found this http://www.java2s.com/Tutorials/Java/Swing_How_to/JList/Create_JList_of_CheckBox.htm
which I optimized a bit. The ACTIVE flag represents the Checkbox, the SELECTED flag shows what entry the cursor sits on.
my version requires a renderer
import java.awt.Component;
import javax.swing.JCheckBox;
import javax.swing.JList;
import javax.swing.ListCellRenderer;
class CheckListRenderer extends JCheckBox implements ListCellRenderer<Entity> {
#Override
public Component getListCellRendererComponent(JList<? extends Entity> list,
Entity value, int index, boolean isSelected, boolean cellHasFocus) {
setEnabled(list.isEnabled());
setSelected(value.isActive()); // sets the checkbox
setFont(list.getFont());
if (isSelected) { // highlights the currently selected entry
setBackground(list.getSelectionBackground());
setForeground(list.getSelectionForeground());
} else {
setBackground(list.getBackground());
setForeground(list.getForeground());
}
setText(value.toString()+" - A" + value.isActive()+" - F"+cellHasFocus+" - S"+isSelected );
return this;
}
}
and an entity that got the active field:
public class Entity {
private boolean active = true;
public boolean isActive() {
return active;
}
public void setActive(boolean isActive) {
this.active = isActive;
}
}
Now you only have to add this to your JList:
list = new JList<Entity>();
list.setModel(new DefaultListModel<Entity>());
list.setCellRenderer(new CheckListRenderer());
list.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
list.addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent event) {
if (event.getX() < 20) {
// Quick and dirty: only change the tick if clicked into the leftmost pixels
#SuppressWarnings("unchecked")
JList<Entity> list = ((JList<Entity>) event.getSource());
int index = list.locationToIndex(event.getPoint());// Get index of item clicked
if (index >= 0) {
Entity item = (Entity) list.getModel().getElementAt(index);
item.setActive(!item.isActive()); // Toggle selected state
list.repaint(list.getCellBounds(index, index));// Repaint cell
}
}
}
});

All of the aggregate components in Swing--that is, components made up other components, such as JTable, JTree, or JComboBox--can be highly customized. For example, a JTable component normally displays a grid of JLabel components, but it can also display JButtons, JTextFields, or even other JTables. Getting these aggregate components to display non-default objects is the easy part, however. Making them respond properly to keyboard and mouse events is a much harder task, due to Swing's separation of components into "renderers" and "editors." This separation was (in my opinion) a poor design choice and only serves to complicate matters when trying to extend Swing components.
To see what I mean, try enhancing Swing's JList component so that it displays checkboxes instead of labels. According to Swing philosophy, this task requires implementing two interfaces: ListCellRenderer (for drawing the checkboxes) and CellEditor (for handling keyboard and mouse events on the checkboxes). Implementing the ListCellRenderer interface is easy enough, but the CellEditor interface can be rather clumsy and hard to understand. In this particular case, I would suggest forgetting CellEditor entirely and to handle input events directly, as shown in the following code.
import javax.swing.*;
import javax.swing.border.*;
import java.awt.*;
import java.awt.event.*;
public class CheckBoxList extends JList
{
protected static Border noFocusBorder = new EmptyBorder(1, 1, 1, 1);
public CheckBoxList()
{
setCellRenderer(new CellRenderer());
addMouseListener(new MouseAdapter()
{
public void mousePressed(MouseEvent e)
{
int index = locationToIndex(e.getPoint());
if (index != -1) {
JCheckBox checkbox = (JCheckBox)
getModel().getElementAt(index);
checkbox.setSelected(
!checkbox.isSelected());
repaint();
}
}
}
);
setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
}
protected class CellRenderer implements ListCellRenderer
{
public Component getListCellRendererComponent(
JList list, Object value, int index,
boolean isSelected, boolean cellHasFocus)
{
JCheckBox checkbox = (JCheckBox) value;
checkbox.setBackground(isSelected ?
getSelectionBackground() : getBackground());
checkbox.setForeground(isSelected ?
getSelectionForeground() : getForeground());
checkbox.setEnabled(isEnabled());
checkbox.setFont(getFont());
checkbox.setFocusPainted(false);
checkbox.setBorderPainted(true);
checkbox.setBorder(isSelected ?
UIManager.getBorder(
"List.focusCellHighlightBorder") : noFocusBorder);
return checkbox;
}
}
}
Here, I intercept mouse clicks from the listbox and simulate a click on the appropriate checkbox. The result is a "CheckBoxList" component that is both simpler and smaller than an equivalent component using the CellEditor interface. To use the class, simply instantiate it, then pass it an array of JCheckBox objects (or subclasses of JCheckBox objects) by calling setListData. Note that the checkboxes in this component will not respond to keypresses (i.e. the spacebar), but you could always add your own key listener if needed.
Source: DevX.com

Here is just a little addition to the JCheckBoxList by Rawa. This will add the ability to select using space bar. If multiple items are selected, all will be set to inverted value of the first item.
addKeyListener(new KeyAdapter() {
#Override
public void keyPressed(KeyEvent e) {
int index = getSelectedIndex();
if (index != -1 && e.getKeyCode() == KeyEvent.VK_SPACE) {
boolean newVal = !((JCheckBox) (getModel()
.getElementAt(index))).isSelected();
for (int i : getSelectedIndices()) {
JCheckBox checkbox = (JCheckBox) getModel()
.getElementAt(i);
checkbox.setSelected(newVal);
repaint();
}
}
}
});

this is yet another example of making list with checkboxes
class JCheckList<T> extends JList<T> {
protected static Border noFocusBorder = new EmptyBorder(1, 1, 1, 1);
public void setSelected(int index) {
if (index != -1) {
JCheckBox checkbox = (JCheckBox) getModel().getElementAt(index);
checkbox.setSelected(
!checkbox.isSelected());
repaint();
}
}
protected static class CellListener
extends DefaultListModel
implements ListDataListener {
ListModel ls;
public CellListener(ListModel ls) {
ls.addListDataListener(this);
int i = ls.getSize();
for (int v = 0; v < i; v++) {
var r = new JCheckBox();
r.setText(ls.getElementAt(v).toString());
this.addElement(r);
}
this.ls = ls;
}
#Override
public void intervalAdded(ListDataEvent e) {
int begin = e.getIndex0();
int end = e.getIndex1();
for (; begin <= end; begin++) {
var r = new JCheckBox();
r.setText(ls.getElementAt(begin).toString());
this.add(begin, r);
}
}
#Override
public void intervalRemoved(ListDataEvent e) {
int begin = e.getIndex0();
int end = e.getIndex1();
for (; begin <= end; end--) {
this.remove(begin);
}
}
#Override
public void contentsChanged(ListDataEvent e) {
}
}
public JCheckList() {
setCellRenderer(new CellRenderer());
addMouseListener(new MouseAdapter() {
public void mousePressed(MouseEvent e) {
int index = locationToIndex(e.getPoint());
setSelected(index);
}
}
);
addKeyListener(new KeyListener(){
#Override
public void keyTyped(KeyEvent e) {
}
#Override
public void keyPressed(KeyEvent e) {
if (e.getKeyCode() == KeyEvent.VK_SPACE){
int index = JCheckList.this.getSelectedIndex();
setSelected(index);
}
}
#Override
public void keyReleased(KeyEvent e) {
}
});
setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
}
#Override
public void setModel(ListModel<T> d) {
var r = new CellListener(d);
d.addListDataListener(r);
super.setModel(r);
}
protected class CellRenderer implements ListCellRenderer {
public Component getListCellRendererComponent(
JList list, Object value, int index,
boolean isSelected, boolean cellHasFocus) {
JCheckBox checkbox = (JCheckBox) value;
checkbox.setBackground(isSelected
? getSelectionBackground() : getBackground());
checkbox.setForeground(isSelected
? getSelectionForeground() : getForeground());
checkbox.setEnabled(isEnabled());
checkbox.setFont(getFont());
checkbox.setFocusPainted(false);
checkbox.setBorderPainted(true);
checkbox.setBorder(isSelected
? UIManager.getBorder(
"List.focusCellHighlightBorder") : noFocusBorder);
return checkbox;
}
}
}