JComboBox

Question

怎样用Java写出一个下拉表框，点击标签，控制背景颜色？

Answer 1

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
/**
 * show a ComboBox
 * extends JFrame  
 * implements ItemListener
 * @author Lei   2010/12/3
 *@version eclipse-SDK-3.6
 */
class ComboBox extends JFrame implements ItemListener{
JComboBox cb;
JLabel lb;
ComboBox(){
super("This is a ComboBox");

setLayout(new GridLayout(2,1));
setSize(400,300);
Container cp=this.getContentPane();

String []city={"北京","上海","洛阳","郑州"};
cb=new JComboBox(city);
cb.setFont(new Font("Normal",Font.BOLD,20));
lb=new JLabel("Please choose a city");
lb.setFont(new Font("Normal",Font.BOLD,20));
cb.setEditable(true);
cp.add(cb);
cp.add(lb);
setVisible(true);
//pack();
cb.addItemListener(this);
addWindowListener(new WindowAdapter(){
       public void windowClosing(WindowEvent e){System.exit(0);}});
}
/**
 * this is the method required by the Interface ItemListener
 * to set the action when the ComboBox is clicked
 * @param ItemEvent e
 */
public void itemStateChanged(ItemEvent e){
if(e.getSource()==cb){
lb.setText("您选择了"+cb.getSelectedItem());
}
}
public static void main(String sd[]){
//Create a object of ComboBox to start the program
ComboBox frm=new ComboBox();
}
}
这是我今天下午刚写的一个JComboBox的程序，先发给你，稍微改一下就能得到你想要的结果，如果可以了就把分给我吧？？！！如果不行的话说一声我帮你改！

Answer 2

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class JComboBoxExample extends JFrame {
    private Color[] colors = {Color.BLUE,Color.RED,Color.BLACK,Color.YELLOW};
    private JComboBox colorSelector = new JComboBox(colors);
    public JComboBoxExample(){
super("JComboBoxExample"); final JPanel container = (JPanel)getContentPane();
colorSelector.setOpaque(false);
colorSelector.addItemListener(new ItemListener(){
@Override public void itemStateChanged(ItemEvent e){
    container.setBackground((Color)(colorSelector.getSelectedItem()));
}
    });
colorSelector.setRenderer(new DefaultListCellRenderer(){
@Override public Component getListCellRendererComponent(JList list,
Object value,
int index,
boolean isSelected,
boolean cellHasFocus){
    setText(value.toString());
    setForeground((Color)value);
    return this;
}
    });
container.setBackground((Color)(colorSelector.getSelectedItem()));
container.add(colorSelector,BorderLayout.NORTH);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setPreferredSize(new Dimension(400,300));
pack();
setVisible(true);
    }    public static void main(final String[] args) {
java.awt.EventQueue.invokeLater(new Runnable(){
public void run(){
    new JComboBoxExample();
}
    });
    }
}