java.util

Class TimerTask

java.lang.Object

java.util.TimerTask

All Implemented Interfaces:

Runnable

public abstract class TimerTask
extends Object
implements Runnable

Task that can be run at a later time if given to a Timer. The TimerTask must implement a run method that will be called by the Timer when the task is scheduled for execution. The task can check when it should have been scheduled and cancel itself when no longer needed.

Example:

  Timer timer = new Timer();
  TimerTask task = new TimerTask() {
      public void run() {
      if (this.scheduledExecutionTime() < System.currentTimeMillis() + 500)
          // Do something
      else
          // Complain: We are more then half a second late!
      if (someStopCondition)
          this.cancel(); // This was our last execution
  };
  timer.scheduleAtFixedRate(task, 1000, 1000); // schedule every second
 

Note that a TimerTask object is a one shot object and can only given once to a Timer. (The Timer will use the TimerTask object for bookkeeping, in this implementation).

This class also implements Runnable to make it possible to give a TimerTask directly as a target to a Thread.

Since:

1.3

Author:

Mark Wielaard (mark@klomp.org)

See Also:

Timer

Method Summary

Modifier and Type	Method and Description
boolean	cancel() Marks the task as canceled and prevents any further execution.
abstract void	run() Method that is called when this task is scheduled for execution.
long	scheduledExecutionTime() Returns the last time this task was scheduled or (when called by the task from the run method) the time the current execution of the task was scheduled.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

cancel

public boolean cancel()

Marks the task as canceled and prevents any further execution. Returns true if the task was scheduled for any execution in the future and this cancel operation prevents that execution from happening.

A task that has been canceled can never be scheduled again.

In this implementation the TimerTask it is possible that the Timer does keep a reference to the TimerTask until the first time the TimerTask is actually scheduled. But the reference will disappear immediatly when cancel is called from within the TimerTask run method.

run

public abstract void run()

Method that is called when this task is scheduled for execution.

Specified by:

run in interface Runnable

scheduledExecutionTime

public long scheduledExecutionTime()

Returns the last time this task was scheduled or (when called by the task from the run method) the time the current execution of the task was scheduled. When the task has not yet run the return value is undefined.

Can be used (when the task is scheduled at fixed rate) to see the difference between the requested schedule time and the actual time that can be found with System.currentTimeMillis().