import java.awt.Dimension;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
/**
 * This class is a simple JFrame implementation to explain how to
 * display time dynamically on the JSwing-based interface.
 * @author Edison
 *
 */
public class TimeFrame extends JFrame
{
 /*
 * Variables 
 */
 private JPanel timePanel;
 private JLabel timeLabel;
 private JLabel displayArea;
 private String DEFAULT_TIME_FORMAT = "HH:mm:ss";
 private String time;
 private int ONE_SECOND = 1000;
 
 public TimeFrame()
 {
 timePanel = new JPanel();
 timeLabel = new JLabel("CurrentTime: ");
 displayArea = new JLabel();
 
 configTimeArea();
 
 timePanel.add(timeLabel);
 timePanel.add(displayArea);
 this.add(timePanel);
 this.setDefaultCloseOperation(EXIT_ON_CLOSE);
 this.setSize(new Dimension(200,70));
 this.setLocationRelativeTo(null);
 }
 
 /**
 * This method creates a timer task to update the time per second
 */
 private void configTimeArea() {
 Timer tmr = new Timer();
 tmr.scheduleAtFixedRate(new JLabelTimerTask(),new Date(), ONE_SECOND);
 }
 
 /**
 * Timer task to update the time display area
 *
 */
 protected class JLabelTimerTask extends TimerTask{
 SimpleDateFormat dateFormatter = new SimpleDateFormat(DEFAULT_TIME_FORMAT);
 @Override
 public void run() {
  time = dateFormatter.format(Calendar.getInstance().getTime());
  displayArea.setText(time);
 }
 }
 
 public static void main(String arg[])
 {
 TimeFrame timeFrame=new TimeFrame();
 timeFrame.setVisible(true); 
 } 
}

繼承TimerTask來創(chuàng)建一個自定義的task，獲取當(dāng)前時間，更新displayArea.
然后創(chuàng)建一個timer的實例，每1秒執(zhí)行一次timertask。由于用schedule可能會有時間誤差產(chǎn)生，所以直接調(diào)用精度更高的scheduleAtFixedRate的。

2. 方法二：利用線程：

這個就比較簡單了。具體代碼如下：

import java.awt.Dimension;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
/**
 * This class is a simple JFrame implementation to explain how to
 * display time dynamically on the JSwing-based interface.
 * @author Edison
 *
 */
public class DTimeFrame2 extends JFrame implements Runnable{
 private JFrame frame;
 private JPanel timePanel;
 private JLabel timeLabel;
 private JLabel displayArea;
 private String DEFAULT_TIME_FORMAT = "HH:mm:ss";
 private int ONE_SECOND = 1000;
 
 public DTimeFrame2()
 {
 timePanel = new JPanel();
 timeLabel = new JLabel("CurrentTime: ");
 displayArea = new JLabel();
 
 timePanel.add(timeLabel);
 timePanel.add(displayArea);
 this.add(timePanel);
 this.setDefaultCloseOperation(EXIT_ON_CLOSE);
 this.setSize(new Dimension(200,70));
 this.setLocationRelativeTo(null);
 }
 public void run()
 {
 while(true)
 {
  SimpleDateFormat dateFormatter = new SimpleDateFormat(DEFAULT_TIME_FORMAT);
  displayArea.setText(dateFormatter.format(
     Calendar.getInstance().getTime()));
  try
  {
  Thread.sleep(ONE_SECOND); 
  }
  catch(Exception e)
  {
  displayArea.setText("Error!!!");
  }
 } 
 } 
 
 public static void main(String arg[])
 {
 DTimeFrame2 df2=new DTimeFrame2();
 df2.setVisible(true);
 
 Thread thread1=new Thread(df2);
 thread1.start(); 
 } 
}

比較：

個人傾向于方法一，因為Timer是可以被多個TimerTask共用，而產(chǎn)生一個線程，會增加多線程的維護(hù)復(fù)雜度。

注意如下代碼：

jFrame.setDefaultCloseOperation(); // 給關(guān)閉按鈕增加特定行為
jFrame.setLocationRelativeTo(null); // 讓Frame一出來就在屏幕中間，而不是左上方。

將上面方法一稍微一修改，就可以顯示多國時間。代碼如下：

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;
import java.util.Timer;
import java.util.TimerTask;
import javax.swing.DefaultComboBoxModel;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
/**
 * A simple world clock
 * @author Edison
 *
 */
public class WorldTimeFrame extends JFrame
{
 /**
 * 
 */
 private static final long serialVersionUID = 4782486524987801209L;
 
 private String time;
 private JPanel timePanel;
 private TimeZone timeZone;
 private JComboBox zoneBox;
 private JLabel displayArea;
 
 private int ONE_SECOND = 1000;
 private String DEFAULT_FORMAT = "EEE d MMM, HH:mm:ss";
 
 public WorldTimeFrame()
 {
 zoneBox = new JComboBox();
 timePanel = new JPanel();
 displayArea = new JLabel();
 timeZone = TimeZone.getDefault();
 
 zoneBox.setModel(new DefaultComboBoxModel(TimeZone.getAvailableIDs()));
 
 zoneBox.addActionListener(new ActionListener(){
  @Override
  public void actionPerformed(ActionEvent e) {
  updateTimeZone(TimeZone.getTimeZone((String) zoneBox.getSelectedItem()));
  }
  
 });
 
 configTimeArea();
 
 timePanel.add(displayArea);
 this.setLayout(new BorderLayout());
 this.add(zoneBox, BorderLayout.NORTH);
 this.add(timePanel, BorderLayout.CENTER);
 this.setLocationRelativeTo(null);
 this.setDefaultCloseOperation(EXIT_ON_CLOSE);
 this.setVisible(true);
 pack();
 }
 
 /**
 * This method creates a timer task to update the time per second
 */
 private void configTimeArea() {
 Timer tmr = new Timer();
 tmr.scheduleAtFixedRate(new JLabelTimerTask(),new Date(), ONE_SECOND);
 }
 
 /**
 * Timer task to update the time display area
 *
 */
 public class JLabelTimerTask extends TimerTask{
 SimpleDateFormat dateFormatter = new SimpleDateFormat(DEFAULT_FORMAT, Locale.ENGLISH);
 @Override
 public void run() {
  dateFormatter.setTimeZone(timeZone);
  time = dateFormatter.format(Calendar.getInstance().getTime());
  displayArea.setText(time);
 }
 }
 
 /**
 * Update the timeZone
 * @param newZone
 */
 public void updateTimeZone(TimeZone newZone)
 {
 this.timeZone = newZone;
 }
 
 public static void main(String arg[])
 {
 new WorldTimeFrame();
 } 
}

本來需要在updateTimeZone(TimeZone newZone)中，更新displayArea的。但是考慮到TimerTask執(zhí)行的時間太短，才1秒鐘，以肉眼觀察，基本上是和立刻更新沒區(qū)別。如果TimerTask執(zhí)行時間長的話，這里就要立刻重新用心的時間更新一下displayArea。

補(bǔ)充：

①. pack() 用來自動計算屏幕大??；
②. TimeZone.getAvailableIDs() 用來獲取所有的TimeZone。

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