List boxes
List boxes are significantly different from JComboBox boxes, and not just in appearance. While a JComboBox box drops down when you activate it, a JList occupies some fixed number of lines on a screen all the time and doesn’t change. If you want to see the items in a list, you simply call getSelectedValues( ), which produces an array of String of the items that have been selected.
A JList allows multiple selection; if you control-click on more than one item (holding down the “control” key while performing additional mouse clicks), the original item stays highlighted and you can select as many as you want. If you select an item, then shift-click on another item, all the items in the span between the two are selected. To remove an item from a group, you can control-click it.
//: c14:List.java
// <applet code=List width=250 height=375></applet>
import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.border.*;
import com.bruceeckel.swing.*;
public class List extends JApplet {
private String[] flavors = {
"Chocolate", "Strawberry", "Vanilla Fudge Swirl",
"Mint Chip", "Mocha Almond Fudge", "Rum Raisin",
"Praline Cream", "Mud Pie"
};
private DefaultListModel lItems=new DefaultListModel();
private JList lst = new JList(lItems);
private JTextArea t =
new JTextArea(flavors.length, 20);
private JButton b = new JButton("Add Item");
private ActionListener bl = new ActionListener() {
public void actionPerformed(ActionEvent e) {
if(count < flavors.length) {
lItems.add(0, flavors[count++]);
} else {
// Disable, since there are no more
// flavors left to be added to the List
b.setEnabled(false);
}
}
};
private ListSelectionListener ll =
new ListSelectionListener() {
public void valueChanged(ListSelectionEvent e) {
if(e.getValueIsAdjusting()) return;
t.setText("");
Object[] items=lst.getSelectedValues();
for(int i = 0; i < items.length; i++)
t.append(items[i] + "\n");
}
};
private int count = 0;
public void init() {
Container cp = getContentPane();
t.setEditable(false);
cp.setLayout(new FlowLayout());
// Create Borders for components:
Border brd = BorderFactory.createMatteBorder(
1, 1, 2, 2, Color.BLACK);
lst.setBorder(brd);
t.setBorder(brd);
// Add the first four items to the List
for(int i = 0; i < 4; i++)
lItems.addElement(flavors[count++]);
// Add items to the Content Pane for Display
cp.add(t);
cp.add(lst);
cp.add(b);
// Register event listeners
lst.addListSelectionListener(ll);
b.addActionListener(bl);
}
public static void main(String[] args) {
Console.run(new List(), 250, 375);
}
} ///:~
You can see that borders have also been added to the lists.
If you just want to put an array of Strings into a JList, there’s a much simpler solution; you pass the array to the JList constructor, and it builds the list automatically. The only reason for using the “list model” in the preceding example is so that the list could be manipulated during the execution of the program.
JLists do not automatically provide direct support for scrolling. Of course, all you need to do is wrap the JList in a JScrollPane, and the details are automatically managed for you.
