import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

import javax.swing.border.*;

import java.util.*;

import java.text.SimpleDateFormat;

/**

 * <p>Title: ComboBox下拉域演示</p>

 * <p>Description: 通过选择或这输入一种日期格式来格式化今天的日期</p>

 * <p>Copyright: Copyright (c) 2014</p>

 * <p>Filename: ComboBoxDemo.java</p>

 * @author 王海涛

 * @version 0.1

 */

public class ComboBoxDemo extends JPanel

                           implements ActionListener {

    static JFrame frame;

    JLabel result;

    String currentPattern;

/**

 *<br>方法说明：构造器。

初始化窗口构件

 *<br>输入參数：

 *<br>返回类型：

 */

    public ComboBoxDemo() {

        setLayout(new BoxLayout(this, BoxLayout.PAGE_AXIS));

        String[] patternExamples = {

                 "dd MMMMM yyyy",

                 "dd.MM.yy",

                 "MM/dd/yy",

                 "yyyy.MM.dd G 'at' hh:mm:ss z",

                 "EEE, MMM d, ''yy",

                 "h:mm a",

                 "H:mm:ss:SSS",

                 "K:mm a,z",

                 "yyyy.MMMMM.dd GGG hh:mm aaa"

                 };

        currentPattern = patternExamples[0];

        //设置一个规范的用户界面

        JLabel patternLabel2 = new JLabel("从下拉列表中选择一种：");

        JComboBox patternList = new JComboBox(patternExamples);

        patternList.addActionListener(this);//patternList的监视器是这个面板

        patternList.setForeground(Color.yellow);

        //创建一个显示结果用户界面

        JLabel resultLabel = new JLabel("当前 日期/时间",

                                        JLabel.LEADING);//相当于LEFT

        result = new JLabel();

        result.setForeground(Color.black);

        result.setBorder(BorderFactory.createCompoundBorder(

             BorderFactory.createLineBorder(Color.cyan),

             BorderFactory.createEmptyBorder(7,7,7,7)

        ));

        //布置构件

        JPanel patternPanel = new JPanel();

        patternPanel.setLayout(new BoxLayout(patternPanel,

                               BoxLayout.PAGE_AXIS));

        patternPanel.add(patternLabel2);

        patternList.setAlignmentX(Component.LEFT_ALIGNMENT);

        patternPanel.add(patternList);

        JPanel resultPanel = new JPanel(new GridLayout(2, 1));//新建一个网格视图的面板

        resultPanel.add(resultLabel);

        resultPanel.add(result);

        patternPanel.setAlignmentX(Component.LEFT_ALIGNMENT);

        resultPanel.setAlignmentX(Component.LEFT_ALIGNMENT);

        add(patternPanel);

        add(Box.createRigidArea(new Dimension(0, 10)));

        add(resultPanel);

        setBorder(BorderFactory.createEmptyBorder(20,20,20,20));

        reformat();

    }

/**

 *<br>方法说明：事件处理

 *<br>输入參数：

 *<br>返回类型：

 */

    public void actionPerformed(ActionEvent e) { //patternList监视器

        JComboBox cb = (JComboBox)e.getSource();

        String newSelection = (String)cb.getSelectedItem();

        currentPattern = newSelection;

        reformat();

    }

/**

 *<br>方法说明：格式和显示今天的日期

 *<br>输入參数：

 *<br>返回类型：

 */

    public void reformat() {

        Date today = new Date();

        SimpleDateFormat formatter =

           new SimpleDateFormat(currentPattern);

        try {

            String dateString = formatter.format(today);

            result.setForeground(Color.red);

            result.setText(dateString);

        } catch (IllegalArgumentException iae) {

            result.setForeground(Color.red);

            result.setText("Error: " + iae.getMessage());

        }

    }

/**

 *<br>方法说明：主方法

 *<br>输入參数：

 *<br>返回类型：

 */

    public static void main(String[] args) {

        JFrame.setDefaultLookAndFeelDecorated(true);

        //创建一个窗口

        frame = new JFrame("ComboBox");

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //创建一个面版容器

        JComponent newContentPane = new ComboBoxDemo();

        newContentPane.setOpaque(true);

        frame.setContentPane(newContentPane);

        frame.setForeground(Color.cyan);

        //显示窗口

        frame.pack();

        frame.setVisible(true);

    }

}