java.util: abstract public class: TimerTask

java.util
abstract public class: TimerTask [javadoc | source]

java.lang.Object
   java.util.TimerTask

All Implemented Interfaces:
Runnable

Direct Known Subclasses:
TimerAlarmClock

A task that can be scheduled for one-time or repeated execution by a Timer.

Also see:

Timer

author: Josh - Bloch

since: 1.3 -

Field Summary
final Object	lock	This object is used to control access to the TimerTask internals.
int	state	The state of this task, chosen from the constants below.
static final int	VIRGIN	This task has not yet been scheduled.
static final int	SCHEDULED	This task is scheduled for execution. If it is a non-repeating task, it has not yet been executed.
static final int	EXECUTED	This non-repeating task has already executed (or is currently executing) and has not been cancelled.
static final int	CANCELLED	This task has been cancelled (with a call to TimerTask.cancel).
long	nextExecutionTime	Next execution time for this task in the format returned by System.currentTimeMillis, assuming this task is scheduled for execution. For repeating tasks, this field is updated prior to each task execution.
long	period	Period in milliseconds for repeating tasks. A positive value indicates fixed-rate execution. A negative value indicates fixed-delay execution. A value of 0 indicates a non-repeating task.

Constructor:
protected TimerTask() { } Creates a new timer task.

Constructor:

 protected TimerTask() {

}

Creates a new timer task.

Method from java.util.TimerTask Summary:
cancel, run, scheduledExecutionTime

Methods from java.lang.Object:
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method from java.util.TimerTask Detail:
public boolean cancel() { synchronized(lock) { boolean result = (state == SCHEDULED); state = CANCELLED; return result; } } Cancels this timer task. If the task has been scheduled for one-time execution and has not yet run, or has not yet been scheduled, it will never run. If the task has been scheduled for repeated execution, it will never run again. (If the task is running when this call occurs, the task will run to completion, but will never run again.) Note that calling this method from within the `run` method of a repeating timer task absolutely guarantees that the timer task will not run again. This method may be called repeatedly; the second and subsequent calls have no effect.
abstract public void run() The action to be performed by this timer task.
public long scheduledExecutionTime() { synchronized(lock) { return (period < 0 ? nextExecutionTime + period : nextExecutionTime - period); } } Returns the scheduled execution time of the most recent actual execution of this task. (If this method is invoked while task execution is in progress, the return value is the scheduled execution time of the ongoing task execution.) This method is typically invoked from within a task's run method, to determine whether the current execution of the task is sufficiently timely to warrant performing the scheduled activity: public void run() { if (System.currentTimeMillis() - scheduledExecutionTime() >= MAX_TARDINESS) return; // Too late; skip this execution. // Perform the task } This method is typically not used in conjunction with fixed-delay execution repeating tasks, as their scheduled execution times are allowed to drift over time, and so are not terribly significant.

Method from java.util.TimerTask Detail:

 public boolean cancel() {
        synchronized(lock) {
            boolean result = (state == SCHEDULED);
            state = CANCELLED;
            return result;
        }
}

Note that calling this method from within the run method of a repeating timer task absolutely guarantees that the timer task will not run again.

This method may be called repeatedly; the second and subsequent calls have no effect.

 abstract public  void run()The action to be performed by this timer task.

 public long scheduledExecutionTime() {
        synchronized(lock) {
            return (period <  0 ? nextExecutionTime + period
                               : nextExecutionTime - period);
        }
}

scheduled

actual

This method is typically invoked from within a task's run method, to determine whether the current execution of the task is sufficiently timely to warrant performing the scheduled activity:

public void run() {
if (System.currentTimeMillis() - scheduledExecutionTime() >=
MAX_TARDINESS)
return; // Too late; skip this execution.
// Perform the task
}

not

fixed-delay execution