Java实现时间动态显示方法汇总

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：

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：

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：

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：

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。