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      如果要在程序中定时执行任务,可以使用java.util.Timer这个类实现。使用Timer类需要一个继承了java.util.TimerTask的类。TimerTask是一个虚类,需要实现它的run方法,实际上是他implements了Runnable接口,而把run方法留给子类实现。
      下面是我的一个例子:

class Worker extends TimerTask {
  
public void run() {
    System.
out.println("我在工作啦!");
  }

}

      Timer类用schedule方法或者scheduleAtFixedRate方法启动定时执行,schedule重载了四个版本,scheduleAtFixedRate重载了两个。每个方法的实现都不同,下面是每个方法的说明:

schedule

public void schedule(TimerTask task,
                     long delay)
Schedules the specified task for execution after the specified delay.

Parameters:
task - task to be scheduled.
delay - delay in milliseconds before task is to be executed.
Throws:
IllegalArgumentException - if delay is negative, or delay + System.currentTimeMillis() is negative.
IllegalStateException - if task was already scheduled or cancelled, or timer was cancelled.
说明:该方法会在设定的延时后执行一次任务。

schedule

public void schedule(TimerTask task,
                     Date time)
Schedules the specified task for execution at the specified time. If the time is in the past, the task is scheduled for immediate execution.

Parameters:
task - task to be scheduled.
time - time at which task is to be executed.
Throws:
IllegalArgumentException - if time.getTime() is negative.
IllegalStateException - if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated.
说明:该方法会在指定的时间点执行一次任务。

schedule

public void schedule(TimerTask task,
                     long delay,
                     long period)
Schedules the specified task for repeated fixed-delay execution, beginning after the specified delay. Subsequent executions take place at approximately regular intervals separated by the specified period.

In fixed-delay execution, each execution is scheduled relative to the actual execution time of the previous execution. If an execution is delayed for any reason (such as garbage collection or other background activity), subsequent executions will be delayed as well. In the long run, the frequency of execution will generally be slightly lower than the reciprocal of the specified period (assuming the system clock underlying Object.wait(long) is accurate).

Fixed-delay execution is appropriate for recurring activities that require "smoothness." In other words, it is appropriate for activities where it is more important to keep the frequency accurate in the short run than in the long run. This includes most animation tasks, such as blinking a cursor at regular intervals. It also includes tasks wherein regular activity is performed in response to human input, such as automatically repeating a character as long as a key is held down.

Parameters:
task - task to be scheduled.
delay - delay in milliseconds before task is to be executed.
period - time in milliseconds between successive task executions.
Throws:
IllegalArgumentException - if delay is negative, or delay + System.currentTimeMillis() is negative.
IllegalStateException - if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated.
说明:该方法会在指定的延时后执行任务,并且在设定的周期定时执行任务。

schedule

public void schedule(TimerTask task,
                     Date firstTime,
                     long period)
Schedules the specified task for repeated fixed-delay execution, beginning at the specified time. Subsequent executions take place at approximately regular intervals, separated by the specified period.

In fixed-delay execution, each execution is scheduled relative to the actual execution time of the previous execution. If an execution is delayed for any reason (such as garbage collection or other background activity), subsequent executions will be delayed as well. In the long run, the frequency of execution will generally be slightly lower than the reciprocal of the specified period (assuming the system clock underlying Object.wait(long) is accurate).

Fixed-delay execution is appropriate for recurring activities that require "smoothness." In other words, it is appropriate for activities where it is more important to keep the frequency accurate in the short run than in the long run. This includes most animation tasks, such as blinking a cursor at regular intervals. It also includes tasks wherein regular activity is performed in response to human input, such as automatically repeating a character as long as a key is held down.

Parameters:
task - task to be scheduled.
firstTime - First time at which task is to be executed.
period - time in milliseconds between successive task executions.
Throws:
IllegalArgumentException - if time.getTime() is negative.
IllegalStateException - if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated.
说明:该方法会在指定的时间点执行任务,然后从该时间点开始,在设定的周期定时执行任务。特别的,如果设定的时间点在当前时间之前,任务会被马上执行,然后开始按照设定的周期定时执行任务。

scheduleAtFixedRate

public void scheduleAtFixedRate(TimerTask task,
                                long delay,
                                long period)
Schedules the specified task for repeated fixed-rate execution, beginning after the specified delay. Subsequent executions take place at approximately regular intervals, separated by the specified period.

In fixed-rate execution, each execution is scheduled relative to the scheduled execution time of the initial execution. If an execution is delayed for any reason (such as garbage collection or other background activity), two or more executions will occur in rapid succession to "catch up." In the long run, the frequency of execution will be exactly the reciprocal of the specified period (assuming the system clock underlying Object.wait(long) is accurate).

Fixed-rate execution is appropriate for recurring activities that are sensitive to absolute time, such as ringing a chime every hour on the hour, or running scheduled maintenance every day at a particular time. It is also appropriate for recurring activities where the total time to perform a fixed number of executions is important, such as a countdown timer that ticks once every second for ten seconds. Finally, fixed-rate execution is appropriate for scheduling multiple repeating timer tasks that must remain synchronized with respect to one another.

Parameters:
task - task to be scheduled.
delay - delay in milliseconds before task is to be executed.
period - time in milliseconds between successive task executions.
Throws:
IllegalArgumentException - if delay is negative, or delay + System.currentTimeMillis() is negative.
IllegalStateException - if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated.
说明:该方法和schedule的相同参数的版本类似,不同的是,如果该任务因为某些原因(例如垃圾收集)而延迟执行,那么接下来的任务会尽可能的快速执行,以赶上特定的时间点。

scheduleAtFixedRate

public void scheduleAtFixedRate(TimerTask task,
                                Date firstTime,
                                long period)
Schedules the specified task for repeated fixed-rate execution, beginning at the specified time. Subsequent executions take place at approximately regular intervals, separated by the specified period.

In fixed-rate execution, each execution is scheduled relative to the scheduled execution time of the initial execution. If an execution is delayed for any reason (such as garbage collection or other background activity), two or more executions will occur in rapid succession to "catch up." In the long run, the frequency of execution will be exactly the reciprocal of the specified period (assuming the system clock underlying Object.wait(long) is accurate).

Fixed-rate execution is appropriate for recurring activities that are sensitive to absolute time, such as ringing a chime every hour on the hour, or running scheduled maintenance every day at a particular time. It is also appropriate for recurring activities where the total time to perform a fixed number of executions is important, such as a countdown timer that ticks once every second for ten seconds. Finally, fixed-rate execution is appropriate for scheduling multiple repeating timer tasks that must remain synchronized with respect to one another.

Parameters:
task - task to be scheduled.
firstTime - First time at which task is to be executed.
period - time in milliseconds between successive task executions.
Throws:
IllegalArgumentException - if time.getTime() is negative.
IllegalStateException - if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated.
说明:和上一个方法类似。

      下面是我的一个测试片断:

  public static void main(String[] args) throws Exception {
    Timer timer 
= new Timer(false);
    timer.schedule(
new Worker(), new Date(System.currentTimeMillis() + 1000));
  }
posted on 2005-06-09 10:29 小米 阅读(33689) 评论(7)  编辑  收藏 所属分类: Java

评论:
# re: 用java.util.Timer定时执行任务 2005-11-28 10:12 | JSDGJKGH
JVDFHDVNDFFKUFUDRU;RTUDNGHKDFKLGJA...OODWWEWEWWEFTR  回复  更多评论
  
# re: 用java.util.Timer定时执行任务 2006-03-09 22:51 | Kornelius
發現跟swing一起import的時候
會衝到
reference to Timer is ambiguous, both class javax.swing.Timer in javax.swing and class java.util.Timer in java.util match  回复  更多评论
  
# re: 用java.util.Timer定时执行任务 2008-01-12 00:14 | 张琼
谢谢你的代码,我学到很多东西。。  回复  更多评论
  
# re: 用java.util.Timer定时执行任务 2009-03-17 09:28 | 2点
顶~~~~好东西!!!  回复  更多评论
  
# re: 用java.util.Timer定时执行任务 2009-03-18 16:50 | ewqr
ewrqewrqewrrwqe  回复  更多评论
  
# re: 用java.util.Timer定时执行任务[未登录] 2011-09-08 16:01 | linugb118
如果timer已经启动,这个时候调整系统时候好像是没有用的。同样如果timer设置了10分钟,自己将系统时间调整到10分种后,也是无效的,说明timer只是在第一次初始化的时候才去取系统时间,后面都不去取的  回复  更多评论
  
# re: 用java.util.Timer定时执行任务 2015-11-12 23:23 | yunp
public static void main(String[] args) throws Exception {
Timer timer = new Timer(false);
timer.schedule(new Worker(), new Date(System.currentTimeMillis() + 1000));
}

time不用执行timer.cancel();方法退出吗?如果有成千上万个这个任务,一直不退出会不会泄漏?  回复  更多评论
  

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