時間動態顯示
1.方法一 用TimerTask
利用java.util.Timer和java.util.TimerTask來做動態更新，畢竟每次更新可以看作是計時1秒發生一次。
代碼如下：
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來建立一個自訂的task，擷取目前時間，更新displayArea.
然後建立一個timer的執行個體，每1秒執行一次timertask。由於用schedule可能會有時間誤差產生，所以直接調用精度更高的scheduleAtFixedRate的。
2. 方法二：利用線程
這個就比較簡單了。
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：
個人傾向於方法一，因為Timer是可以被多個TimerTask共用，而產生一個線程，會增加多線程的維護複雜度。
TIPS：
jFrame.setDefaultCloseOperation(); // 給關閉按鈕增加特定行為
jFrame.setLocationRelativeTo(null); // 讓Frame一出來就在螢幕中間，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();
}
} |
TBD:
本來需要在updateTimeZone(TimeZone newZone)中，更新displayArea的。但是考慮到TimerTask執行的時間太短，才1秒鐘，以肉眼觀察，基本上是和立刻更新沒區別。如果TimerTask執行時間長的話，這裡就要立刻重新用心的時間更新一下displayArea。
TIPS：
a. pack() 用來自動計算螢幕大小；
b. TimeZone.getAvailableIDs() 用來擷取所有的TimeZone。
