Listing 9.1  JList Used to Create a Leap Year List (TJList1.java)
// Demonstrates how to use the ListModel and JList component

/*
 * <Applet code = TJList1 width = 200 height = 175>
 * </Applet>
 */
import javax.swing.*;
import java.awt.*;

public class TJList1 extends JApplet {
    // 1. Define the data members.
    JList list = null;
    MyListModel model = null;
    JScrollPane scrollPane = null;
    Container container = null;

    public void init() {
        // 2. Get a handle to the applet's content pane and
        // set the grid layout.
        container = this.getContentPane();
        container.setLayout(new GridLayout(1,1));

        // 3. Create objects of type JList, MyListModel,
        // and JScrollPane and add them hierarchically
        // to the applet as shown.
        model = new MyListModel();
        list = new JList(model);
        scrollPane = new JScrollPane(list);
        container.add(scrollPane);
    }
}

// 4. Custom list data model that generates leap years.
class MyListModel extends AbstractListModel {
    int startYear = 1900;
    int endYear = 2000;
    int leapYear;
    // 5. Returns each list element (leap year).
    public Object getElementAt(int index) {
        index = index + 1; // index starts from 0;
                           // so make it 1.
        if ((startYear+index)%4 == 0)
            return "Year "+(startYear+index);
        else
            return null;
    }

    // 6. Returns the total count of data; that is,
    // total number of years in the present case.
    public int getSize() {
        return (endYear-startYear);
    }
}

Listing 9.2  JList Creates List Cells with Icons (TJList2.java)
/*
 * <Applet code=TJList2 width=200 height=150>
 * </Applet>
 */

import javax.swing.*;
import java.awt.*;

public class TJList2 extends JApplet {
    // 1. Labels for the list items.
    String[] ComputerComps = {"Monitor", "Key Board", "Mouse",
                              "Joy Stick", "Modem", "CD ROM",
                              "RAM Chip", "Diskette"};

    // 2. Create icons for selections and make an array.
    Icon icon1 = new ImageIcon("monitor.gif");
    Icon icon2 = new ImageIcon("keyboard.gif");
    Icon icon3 = new ImageIcon("mouse.gif");
    Icon icon4 = new ImageIcon("joystick.gif");
    Icon icon5 = new ImageIcon("modem.gif");
    Icon icon6 = new ImageIcon("cdrom.gif");
    Icon icon7 = new ImageIcon("ramchip.gif");
    Icon icon8 = new ImageIcon("diskett.gif");
    Icon[] icons = {icon1, icon2, icon3, icon4,
                    icon5, icon6, icon7, icon8};

    public void init() {
        // 3. Create a list object to display the computer
        //    components.
        JList list = new JList(ComputerComps);

        // 4. Render the list cells with icons.
        list.setCellRenderer(new MyCellRenderer(icons));

        // 5. Add the list to the applet's content pane
        //    through a scrollpane.
        getContentPane().add(new JScrollPane(list));
    }
}


// 6. Class that renders the list cells with icons.
class MyCellRenderer extends JLabel implements ListCellRenderer {
    Icon[] icons;

    public MyCellRenderer (Icon[] icons) {
        this.icons = icons;
        setOpaque(true);
    }

    // 7. Method that must be implemented from the interface
    //    ListCellRenderer.
    public Component getListCellRendererComponent (
                     JList list,
                     Object value,
                     int index,
                     boolean isSelected,
                     boolean cellHasFocus) {

        // 8. Set the text for the label.
        if (value != null) {
            String text = value.toString();
            setText(text);
        }

        // 9. Set the icon for each selection cell
        //    indicated by the index.
            setIcon(icons[index]);

        // 10. What happens when a selection is made.
        if (isSelected) {
            setBackground(list.getSelectionBackground());
            setForeground(list.getSelectionForeground());
        }

        // NOTE: This step is very important; otherwise, the
        // selection colors don't render as expected!
        else {
            setBackground(list.getBackground());
            setForeground(list.getForeground());
        }

        // 11. Finally, return this rubber stamp component.
        return this;
    }
}

Listing 9.3  List Item Selection (TJList3.java)
// Demonstrates the item-selection from a list widget
/*
 * <Applet code=TJList3 width=300 height=200>
 *</Applet>
 */
import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;

public class TJList3 extends JApplet {
    // 1. Declare the required references.
    JList list = null;
    JLabel label = null;
    Container c = null;

    // 2. Create the arrays for the list selections.
    String[] weekdays = {
        "Sunday", "Monday", "Tuesday", "Wednesday",
        "Thursday", "Friday", "Saturday" };
    int[] holidays = {0, 6}; //Indices for sunday&saturday

    public void init() {
        // 3. Get the handle on the applet's content pane.
        c = this.getContentPane();

        // 4. Create a list object.
        list = new JList(weekdays);
        Font f1 = new Font("SansSerif", Font.BOLD, 16);
        list.setFont(f1);
        list.setSelectionMode(
             ListSelectionModel.MULTIPLE_INTERVAL_SELECTION);
        list.setSelectedIndices(holidays);
        list.addSelectionInterval(2, 4);
        list.setSelectionBackground(Color.blue);
        list.setSelectionForeground(Color.white);

        // 5. Registering a listener class.
        ListSelectionListener l = new MyListener();
        list.addListSelectionListener(l);

        // 6. Add the list to a scroll pane and finally to the applet.
        JScrollPane sp = new JScrollPane(list);
        c.add(sp);

        // 7. Create a label object.
        label = new JLabel("Reselect using mouse?", JLabel.CENTER);
        Font f2 = new Font("Serif", Font.BOLD, 26);
        label.setFont(f2);
        label.setOpaque(true);
        label.setBackground(Color.lightGray);
        label.setForeground(Color.black);
        c.add(label, BorderLayout.SOUTH);
    }

    // 8. JList selection event listener class.
    class MyListener implements ListSelectionListener {
        public void valueChanged(ListSelectionEvent evt) {
            label.setText((String) list.getSelectedValue());
        }
    }
}

Listing 9.4  Using Double Mouse Clicks to Select List Components (TJList4.java)
// Demonstrates the List component and double mouse clicks

/*
 * <Applet code = TJList4 width = 400 height = 200>
 * </Applet>
 */
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.Vector;

public class TJList4 extends JApplet {
    // 1. Data members.
    JList prodList = null;
    JList cartList = null;
    String[] products = {
             "Internet Access PlusPack2.0",
             "Java Developer's Companion CD",
             "Java IDL", "Java OS",
             "Java Solutions Guide", "Java Studio",
             "Java Web Server", "Java WorkShop",
             "JavaScope", "JavaSTAR" };
    Container container = null;
    GridBagLayout gridbag = null;
    GridBagConstraints c = null;
    Vector vector = new Vector();
    JScrollPane scrollPane2 = null;
    int index;
    JButton button1, button2;

    public void init() {
        // 2. Prepare the JApplet layout.
        container = this.getContentPane();
        gridbag = new GridBagLayout();
        c = new GridBagConstraints();
        container.setLayout(gridbag);

        // 3. Necessary labels.
        c.fill = GridBagConstraints.BOTH;
        c.gridx = 0; c.gridy = 0;
        c.gridwidth = 2; c.gridheight = 1;
        c.weightx = 0; c.weighty = 0;
        setLabel("Java Products");

        c.gridx = 2;
        setLabel("Shopping Cart");

        // 4. Create a list of Java products.
        c.gridx = 0; c.gridy = 1;
        c.weightx = 1; c.weighty = 1;
        prodList = new JList(products);
        MyMouseListener mListener = new MyMouseListener();
        prodList.addMouseListener(mListener);
        JScrollPane scrollPane1 = new JScrollPane(prodList,
                    JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
                    JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
        gridbag.setConstraints(scrollPane1, c);
        container.add(scrollPane1);

        // 5. Create another list object called cartList.
        c.gridx = 2;
        cartList = new JList();
        scrollPane2 = new JScrollPane(cartList,
                    JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,
                    JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
        gridbag.setConstraints(scrollPane2, c);
        container.add(scrollPane2);

        // 6. Another label indicating what to do.
        c.gridx = 0; c.gridy = 2;
        c.weightx = 0; c.weighty = 0;
        setLabel("Double click to choose");

        // 7. Add a button to delete items.
        c.gridx = 2; c.gridwidth = 1;
        c.fill = GridBagConstraints.NONE;
        button1 = new JButton("Delete Item");
        ButtonListener bl = new ButtonListener();
        button1.addActionListener(bl);
        gridbag.setConstraints(button1, c);
        container.add(button1);

        // 8. A Button to order items.
        c.gridx = 3;
        c.ipadx = 10;
        button2 = new JButton("Order Now");
        gridbag.setConstraints(button2, c);
        container.add(button2);

        container.validate();
    }

    // 9. Supporting method for labels.
    public void setLabel(String text) {
        JLabel label = new JLabel(text, SwingConstants.CENTER);
        gridbag.setConstraints(label, c);
        container.add(label);
    }

    // 10. Listener class that recognizes multiple mouse clicks.
    class MyMouseListener extends MouseAdapter {
        public void mouseClicked(MouseEvent me) {
            if (me.getClickCount() == 2) {
                index = prodList.locationToIndex(me.getPoint());
                prodList.setSelectedIndex(index);
                prodList.setSelectionBackground(Color.blue);
                prodList.setSelectionForeground(Color.white);
                vector.addElement(products[index]);
                cartList.setListData(vector);
                cartList.repaint();
                scrollPane2.repaint();
            }
        }
    }

    // 11. Button listener to delete items from the shopping cart.
    class ButtonListener implements ActionListener {
        public void actionPerformed(ActionEvent ae) {
            Object srcButton = (JButton) ae.getSource();
            if (srcButton == button1 && !cartList.isSelectionEmpty()) {
               index = cartList.getSelectedIndex();
               vector.remove(index);
               cartList.repaint(); 
}
        }
    }
}

Listing 9.5  JComboBox Using the Custom Model (TJComboBox1.java)
/*
 * <Applet code=TJComboBox1 width=400 height=50>
 * </Applet>
 */

import javax.swing.*;
import javax.swing.event.*;

public class TJComboBox1 extends JApplet {
    public void init() {
        // 1. Create a combo box with the custom model.
        JComboBox cbox = new JComboBox(new MyComboBoxModel());

        // 2. Set the number of rows to be visible.
        cbox.setMaximumRowCount(5);

        // 3. Add the combo box object to the applet's content pane.
        getContentPane().add(cbox);
    }
}

// 4. Custom data model for the combo box.
class MyComboBoxModel extends AbstractListModel
                      implements ComboBoxModel {
    String[] ComputerComps = {"Monitor", "Key Board", "Mouse",
                              "Joy Stick", "Modem", "CD ROM",
                              "RAM Chip", "Diskette"};
    String selection = null;

    // Methods implemented from the class AbstractListModel
    public Object getElementAt(int index) {
        return ComputerComps[index];
    }

    public int getSize() {
        return ComputerComps.length;
    }

    public void setSelectedItem(Object anItem) {
        selection = (String) anItem; // to select and register an
    }                                // item from the pull-down list

    // Methods implemented from the interface ComboBoxModel
    public Object getSelectedItem() {
        return selection; // to add the selection to the combo box
    }
}

Listing 9.6  JComboBox Items Rendered with Icons and Labels (TJComboBox2.java)
/*
 * <Applet code=TJComboBox2 width=400 height=50>
 * </Applet>
 */

import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;

public class TJComboBox2 extends JApplet {
    // 1. Labels for the combo box pull-down list.
    String[] ComputerComps = {"Monitor", "Key Board", "Mouse",
                              "Joy Stick", "Modem", "CD ROM",
                              "RAM Chip", "Diskette"};
    // 2. Create icons for selections and make an array.
    Icon icon1 = new ImageIcon("monitor.gif");
    Icon icon2 = new ImageIcon("keyboard.gif");
    Icon icon3 = new ImageIcon("mouse.gif");
    Icon icon4 = new ImageIcon("joystick.gif");
    Icon icon5 = new ImageIcon("modem.gif");
    Icon icon6 = new ImageIcon("cdrom.gif");
    Icon icon7 = new ImageIcon("ramchip.gif");
    Icon icon8 = new ImageIcon("diskett.gif");
    Icon[] icons = {icon1, icon2, icon3, icon4,
                    icon5, icon6, icon7, icon8};
    public void init() {
        // 3. Create a combo box with the custom model.
        JComboBox cbox = new JComboBox(ComputerComps);
        cbox.setRenderer(new MyCellRenderer(icons));

        // 4. Set the number of rows to be visible.
        cbox.setMaximumRowCount(5);

        // 5. Add the combo box object to the applet's content pane.
        getContentPane().add(cbox);
    }
}


// 6. Class that renders the list cells with icons.
class MyCellRenderer extends JLabel implements ListCellRenderer {
    Icon[] icons;

    public MyCellRenderer (Icon[] icons) {
        this.icons = icons;
        setOpaque(true);
    }

    // 7. Method that must be implemented from the interface.
    public Component getListCellRendererComponent (
                     JList list,
                     Object value,
                     int index,
                     boolean isSelected,
                     boolean cellHasFocus) {

        // 8. Set the text for the label.
        if (value != null) {
            String text = value.toString();
            setText(text);
        }

        // 9. Set the icon for each selection cell indicated
        //    by the index.
        if ((index != -1) && (index < icons.length)) {
            setIcon(icons[index]);  
        }

        // 10. What happens when a selection is made.
        if (isSelected) {
            setBackground(list.getSelectionBackground());
            setForeground(list.getSelectionForeground());
        }

        // NOTE: This step is very important; otherwise, the
        // selection colors don't render as expected!
        else {
            setBackground(list.getBackground());
            setForeground(list.getForeground());
        }

        // 11. Finally, return this rubber stamp.
        return this;
    }
}

Listing 9.7  Editable JComboBox (TJComboBox3.java)
// Demonstrates editable combo boxes

/*
 * <Applet code=TJComboBox3 width=450 height=50>
 *</Applet>
 */

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class TJComboBox3 extends JApplet {
    // 1. Declare the references.
    JComboBox cbox = null;
    Container c = null;

    // 2. Define an array of sites to be shown in the
    // combo box pull-down list, by default.
    String[] defaultSites = {
          "http://www.sun.com", "http://www.iisc.ernet.in",
          "http://www.hp.com",  "http://www.ibm.com",
          "http://www.yahoo.com", "http://www.news.com"};
    String defaultEdit = "http://www.javasoft.com";

    public void init() {
        // 3. Get a handle on the applet's content pane.
        // and prepare the container with grid layout
        c = this.getContentPane();
        c.setLayout(new GridLayout(1,2));

        // 4. Create the combo box with the list of default sites.
        cbox = new JComboBox(defaultSites);
        cbox.setOpaque(true);

        // 5. Make the combo box editable.
        cbox.setEditable(true);

        // 6. Configure the combo box editor.
        cbox.configureEditor(cbox.getEditor(), defaultEdit);

        // 7. Rows to be visible without scrollbars.
        cbox.setMaximumRowCount(5);

        // 8. Set the combo box editor colors and font.
        ComboBoxEditor cboxEditor = cbox.getEditor();
        Component editorComp = cboxEditor.getEditorComponent();
        editorComp.setBackground(Color.white);
        editorComp.setForeground(Color.blue);

        Font f1 = new Font("Dialog", Font.PLAIN, 16);
        editorComp.setFont(f1);

        // 9. Font for the combo box popup list.
        cbox.setFont(f1);

        // 10. Register the action listener.
        cbox.addActionListener(new CboxListener());

        // 11. A label to indicate what to do.
        JLabel label = new JLabel("Enter a web site URL:",
                                  JLabel.CENTER);
        label.setFont(new Font("SansSerif", Font.BOLD, 18));

        // 12. Finally...
        c.add(label);
        c.add(cbox);
    }

    class CboxListener implements ActionListener {
        public void actionPerformed(ActionEvent evt) {
            // Helpful flag
            boolean isItemPresent = false;

            // 13. Check if the item already exists in the pop-up list.
            for (int i=0; i<cbox.getItemCount(); i++) {
                if (cbox.getItemAt(i).equals(cbox.getSelectedItem())) {
                    isItemPresent = true;
                    break;
                }
            }

            // 14. If the item is not present in the pop-up list...
            if (!isItemPresent) {
                cbox.insertItemAt(cbox.getSelectedItem(), 0);
                isItemPresent = false;
            }
        }
    }
}