本文所述实例可以实现Java在界面上动态的显示时间。具体实现方法汇总如下:
1.方法一 用TimerTask:
利用java.util.Timer和java.util.TimerTask来做动态更新,毕竟每次更新可以看作是计时1秒发生一次。
代码如下:
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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 ); } } |
继承TimerTask来创建一个自定义的task,获取当前时间,更新displayArea.
然后创建一个timer的实例,每1秒执行一次timertask。由于用schedule可能会有时间误差产生,所以直接调用精度更高的scheduleAtFixedRate的。
2. 方法二:利用线程:
这个就比较简单了。具体代码如下:
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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(); } } |
比较:
个人倾向于方法一,因为Timer是可以被多个TimerTask共用,而产生一个线程,会增加多线程的维护复杂度。
注意如下代码:
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jFrame.setDefaultCloseOperation(); // 给关闭按钮增加特定行为 jFrame.setLocationRelativeTo( null ); // 让Frame一出来就在屏幕中间,而不是左上方。 |
将上面方法一稍微一修改,就可以显示多国时间。代码如下:
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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(); } } |
本来需要在updateTimeZone(TimeZone newZone)中,更新displayArea的。但是考虑到TimerTask执行的时间太短,才1秒钟,以肉眼观察,基本上是和立刻更新没区别。如果TimerTask执行时间长的话,这里就要立刻重新用心的时间更新一下displayArea。
补充:
①. pack() 用来自动计算屏幕大小;
②. TimeZone.getAvailableIDs() 用来获取所有的TimeZone。