【例 11-14】一个说明组合框用法的应用程序。程序中声明的组合框子类实现ItemLister接口和ActionListener接口。组合框子类的窗口中设置了一个文本框和一个组合框，组合框中有三个选择。实现接口的监视方法将组合框的选择结果在文本框中显示。
public class Example6_4{
    public static void main(String args[]){
        ComboBoxDemo mycomboBoxGUI = new ComboBoxDemo();
    }
}
class ComboBoxDemo extends JFrame implements ActionListener,ItemListener{
    public static final int Width = 350;
    public static final int Height = 150;
    String proList[] = { "踢足球","打篮球","打排球" };
    JTextField text;
    JComboBox comboBox;
    public ComboBoxDemo(){
        setSize(Width,Height);
        setTitle("组合框使用示意程序");
        Container conPane = getContentPane();
        conPane.setBackground(Color.BLUE);
        conPane.setLayout(new FlowLayout());
        comboBox = new JComboBox(proList);
        comboBox.addActionListener(this);
        combobox.addItemListener(this);
        comboBox.setEditable(true);//响应键盘输入
        conPane.add(comboBox);
        text = new JTextField(10);
        conPane.add(text);
        this.setVisible(true);
    }
    public void actionPerformed(ActionEvent e){
        if(e.getSource()==comboBox)
            text.setText(comboBox.getSelectedItem().toString());
    }
    public void itemStateChanged(ItemEvent e){
        if(e.getSource()==comboBox){
            text.setText(comboBox.getSelectedItem().toString());
        }
    }
}