以下程序当点击组合框中的选项时，在下面的文本区中将显示相关的信息。例如，当依次点击了“One”、“Two”和“Three”后，显示结果如题28图所示。初始时，组合框中显示“Three”，文本区中显示空白。
题28图
import java.awt.*; import java.awt.event. *; import javax.swing.*;
import javax.swing.border.*;
public class Test28{
public static void main(String[] aargs){
JComboBoxDemo cbd = new JComboBoxDemo);
cbd.go();
}
}
class JComboBoxDemo implements ActionListener{
JFrame frame = new JFrame ("JComboBox Demo");
JComboBox <String> jcb;
JTextArea ta = new JTextArea(0, 30);
JPanel pl = new JPanel(); JPanel p2 = new Jpanel(); JPanel p3 = new JPanel();
String[] itemList = { "One", "Two", "Three", "Four", "Five" };
public void go() {
jcb = new JComboBox<String>(itemList); pl.add(jcb);
jcb.___ _①_____;
Border etched = BorderFactory.createEtchedBorder();
Border border = BorderFactory.createcTitledBorder(etched, "Uneditable");
p.setBorder(border);
JScrollPane jp = new JScrollPane(ta);
p2.setLayou(new BorderLayout()); p2.add(jp);
border = BorderFactory.createTitledBorder(etched,"Results");
p2.setBorde(border);
jcb.__②__________;
p3.setLayout(new BorderL ayout()); p3.add(p1);
Container cp = frame.getContentPane(;
cp.setLayou(new GridLayout(0,1)); cp.add(p3); cp.add(p2);
frame.pack(); frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ ON_CLOSE);
}
public void actionPerformed(ActionEvent e) {
JComboBox jcbcurrent = (JComboBox)e.getSource();
if (jcbcurrent == jcb) {
ta.append("In Item "+___③_ +" inserted");
}
}
}
