import java.awt.*;import java.awt.event.*;import javax.swing.*;import javax.swing.event.*;import java.net.URL;public class ListDataEventDemo extends JApplet                                implements ListSelectionListener {    private JList list;    private DefaultListModel listModel;    private static final String addString = "Add";    private static final String deleteString = "Delete";    private static final String upString = "Move up";    private static final String downString = "Move down";    private JButton addButton;    private JButton deleteButton;    private JButton upButton;    private JButton downButton;    private JTextField nameField;    private JTextArea log;    static private String newline = "\n";    public void init() {        //Create and populate the list model.        listModel = new DefaultListModel();        listModel.addElement("Whistler, Canada");        listModel.addElement("Jackson Hole, Wyoming");        listModel.addElement("Squaw Valley, California");        listModel.addElement("Telluride, Colorado");        listModel.addElement("Taos, New Mexico");        listModel.addElement("Snowbird, Utah");        listModel.addElement("Chamonix, France");        listModel.addElement("Banff, Canada");        listModel.addElement("Arapahoe Basin, Colorado");        listModel.addElement("Kirkwood, California");        listModel.addElement("Sun Valley, Idaho");        listModel.addListDataListener(new MyListDataListener());        //Create the list and put it in a scroll pane.        list = new JList(listModel);        list.setSelectionMode(            ListSelectionModel.SINGLE_INTERVAL_SELECTION);        list.setSelectedIndex(0);        list.addListSelectionListener(this);        JScrollPane listScrollPane = new JScrollPane(list);        //Create the list modifying buttons.        addButton = new JButton(addString);        addButton.setActionCommand(addString);        addButton.addActionListener(new AddButtonListener());        deleteButton = new JButton(deleteString);        deleteButton.setActionCommand(deleteString);        deleteButton.addActionListener(            new DeleteButtonListener());        upButton = new JButton(            new ImageIcon(getURL("images/up.gif")));        upButton.setMargin(new Insets(0,0,0,0));        upButton.setActionCommand(upString);        upButton.addActionListener(new UpDownListener());        downButton = new JButton(            new ImageIcon(getURL("images/down.gif")));        downButton.setMargin(new Insets(0,0,0,0));        downButton.setActionCommand(downString);        downButton.addActionListener(new UpDownListener());        JPanel upDownPanel = new JPanel(new GridLayout(2, 1));        upDownPanel.add(upButton);        upDownPanel.add(downButton);        //Create the text field for entering new names.        nameField = new JTextField(15);        nameField.addActionListener(new AddButtonListener());        String name = listModel.getElementAt(list.getSelectedIndex())                               .toString();        nameField.setText(name);        //Create a control panel (uses the default FlowLayout).        JPanel buttonPane = new JPanel();        buttonPane.add(nameField);        buttonPane.add(addButton);        buttonPane.add(deleteButton);        buttonPane.add(upDownPanel);        //Create the log for reporting list data events.        log = new JTextArea(10, 20);        JScrollPane logScrollPane = new JScrollPane(log);        //Create a split pane for the log and the list.        JSplitPane splitPane = new JSplitPane(JSplitPane.VERTICAL_SPLIT,                                        listScrollPane, logScrollPane);        Container contentPane = getContentPane();        contentPane.add(buttonPane, BorderLayout.NORTH);        contentPane.add(splitPane, BorderLayout.CENTER);    }    class MyListDataListener implements ListDataListener {        public void contentsChanged(ListDataEvent e) {            log.append("contentsChanged: " + e.getIndex0() +                       ", " + e.getIndex1() + newline);         }        public void intervalAdded(ListDataEvent e) {            log.append("intervalAdded: " + e.getIndex0() +                       ", " + e.getIndex1() + newline);         }        public void intervalRemoved(ListDataEvent e) {            log.append("intervalRemoved: " + e.getIndex0() +                       ", " + e.getIndex1() + newline);         }    }    class DeleteButtonListener 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.             */            ListSelectionModel lsm = list.getSelectionModel();            int firstSelected = lsm.getMinSelectionIndex();            int lastSelected = lsm.getMaxSelectionIndex();            listModel.removeRange(firstSelected, lastSelected);            int size = listModel.size();            if (size == 0) {            //List is empty: disable delete, up, and down buttons.                deleteButton.setEnabled(false);                upButton.setEnabled(false);                downButton.setEnabled(false);            } else {            //Adjust the selection.                if (firstSelected == listModel.getSize()) {                //Removed item in last position.                    firstSelected--;                }                list.setSelectedIndex(firstSelected);            }        }    }    /** A listener shared by the text field and add button. */    class AddButtonListener implements ActionListener {        public void actionPerformed(ActionEvent e) {            if (nameField.getText().equals("")) {            //User didn't type in a name...                Toolkit.getDefaultToolkit().beep();                return;            }            int index = list.getSelectedIndex();            int size = listModel.getSize();            //If no selection or if item in last position is selected,            //add the new one to end of list, and select new one.            if (index == -1 || (index+1 == size)) {                listModel.addElement(nameField.getText());                list.setSelectedIndex(size);            //Otherwise insert the new one after the current selection,            //and select new one.            } else {                listModel.insertElementAt(nameField.getText(), index+1);                list.setSelectedIndex(index+1);            }        }    }    //Listen for clicks on the up and down arrow buttons.    class UpDownListener implements ActionListener {        public void actionPerformed(ActionEvent e) {            //This method can be called only when            //there's a valid selection,            //so go ahead and move the list item.            int moveMe = list.getSelectedIndex();            if (e.getActionCommand().equals(upString)) {            //UP ARROW BUTTON                if (moveMe != 0) {                     //not already at top                    swap(moveMe, moveMe-1);                    list.setSelectedIndex(moveMe-1);                    list.ensureIndexIsVisible(moveMe-1);                }            } else {            //DOWN ARROW BUTTON                if (moveMe != listModel.getSize()-1) {                //not already at bottom                    swap(moveMe, moveMe+1);                    list.setSelectedIndex(moveMe+1);                    list.ensureIndexIsVisible(moveMe+1);                }            }        }    }    //Swap two elements in the list.    private void swap(int a, int b) {        Object aObject = listModel.getElementAt(a);        Object bObject = listModel.getElementAt(b);        listModel.set(a, bObject);        listModel.set(b, aObject);    }    //Listener method for list selection changes.    public void valueChanged(ListSelectionEvent e) {        if (e.getValueIsAdjusting() == false) {            if (list.getSelectedIndex() == -1) {            //No selection: disable delete, up, and down buttons.                deleteButton.setEnabled(false);                upButton.setEnabled(false);                downButton.setEnabled(false);                nameField.setText("");            } else if (list.getSelectedIndices().length > 1) {            //Multiple selection: disable up and down buttons.                deleteButton.setEnabled(true);                upButton.setEnabled(false);                downButton.setEnabled(false);            } else {            //Single selection: permit all operations.                deleteButton.setEnabled(true);                upButton.setEnabled(true);                downButton.setEnabled(true);                nameField.setText(list.getSelectedValue().toString());            }        }    }    protected URL getURL(String filename) {        URL codeBase = this.getCodeBase();        URL url = null;        try {            url = new URL(codeBase, filename);        } catch (java.net.MalformedURLException e) {            System.out.println("Couldn't create image: badly specified URL");            return null;        }        return url;    }}