如果要在程序中定時執行任務，可以使用java.util.Timer這個類實現。使用Timer類需要一個繼承了java.util.TimerTask的類。TimerTask是一個虛類，需要實現它的run方法，實際上是他implements了Runnable接口，而把run方法留給子類實現。
下面是我的一個例子：
class
Worker extends TimerTask
{
public
void
run()
{
System.
out
.println(
"
我在工作啦！
"
);
}
}
Timer類用schedule方法或者scheduleAtFixedRate方法啟動定時執行，schedule重載了四個版本，scheduleAtFixedRate重載了兩個。每個方法的實現都不同，下面是每個方法的說明：
schedule
public void
schedule
(
TimerTask
task,
long delay)
task
- task to be scheduled.
delay
- delay in milliseconds before task is to be executed.
IllegalArgumentException
- if
delay
is negative, or
delay + System.currentTimeMillis()
is negative.
IllegalStateException
- if task was already scheduled or cancelled, or timer was cancelled.
說明：該方法會在設定的延時后執行一次任務。
schedule
public void
schedule
(
TimerTask
task,
Date
time)
task
- task to be scheduled.
time
- time at which task is to be executed.
IllegalArgumentException
- if
time.getTime()
is negative.
IllegalStateException
- if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated.
說明：該方法會在指定的時間點執行一次任務。
schedule
public void
schedule
(
TimerTask
task,
long delay,
long 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.
task
- task to be scheduled.
delay
- delay in milliseconds before task is to be executed.
period
- time in milliseconds between successive task executions.
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.
說明：該方法會在指定的延時后執行任務，并且在設定的周期定時執行任務。
schedule
public void
schedule
(
TimerTask
task,
Date
firstTime,
long 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.
task
- task to be scheduled.
firstTime
- First time at which task is to be executed.
period
- time in milliseconds between successive task executions.
IllegalArgumentException
- if
time.getTime()
is negative.
IllegalStateException
- if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated.
說明：該方法會在指定的時間點執行任務，然后從該時間點開始，在設定的周期定時執行任務。特別的，如果設定的時間點在當前時間之前，任務會被馬上執行，然后開始按照設定的周期定時執行任務。
scheduleAtFixedRate
public void
scheduleAtFixedRate
(
TimerTask
task,
long delay,
long 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.
task
- task to be scheduled.
delay
- delay in milliseconds before task is to be executed.
period
- time in milliseconds between successive task executions.
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.
說明：該方法和schedule的相同參數的版本類似，不同的是，如果該任務因為某些原因（例如垃圾收集）而延遲執行，那么接下來的任務會盡可能的快速執行，以趕上特定的時間點。
scheduleAtFixedRate
public void
scheduleAtFixedRate
(
TimerTask
task,
Date
firstTime,
long 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.
task
- task to be scheduled.
firstTime
- First time at which task is to be executed.
period
- time in milliseconds between successive task executions.
IllegalArgumentException
- if
time.getTime()
is negative.
IllegalStateException
- if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated.
說明：和上一個方法類似。
下面是我的一個測試片斷：
public
static
void
main(String[] args) throws Exception
{
Timer timer
=
new
Timer(
false
);
timer.schedule(
new
Worker(),
new
Date(System.currentTimeMillis()
+
1000
));
}
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