Run a ScheduledExecutorService periodically or just once based on condition

Question

I have a specific task which has to be executed periodically, or just once based on a condition. I am using the following approach:

Runnable r = new Runnable() {

        public void run() 
        {       
            //Execute task
        }
    };
final long freq = frequencyOfTask;
ScheduledExecutorService dataTimer = Executors.newScheduledThreadPool(1);
ScheduledFuture<?> dataTimerHandle = dataTimer.scheduleAtFixedRate(r, 0L, freq, TimeUnit.MILLISECONDS);
if(!isDynamic)
{
    dataTimerHandle.cancel(false); //cancel the event in main thread while asking the already submitted tasks to complete.
}

The task runs fine for the case where isDynamic is false , ie, where the task is not cancelled. But, for the other case (when the execution is required just once ) it doesn't execute at all.

Answer 1

It doesn't execute because you're cancelling the task before it has a chance to run even once - scheduleAtFixedRate will return immediately and allow your method to continue executing, and the first thing it does is to cancel the as-yet-unexecuted task.

Instead of scheduling the task and then cancelling it, just submit it as a non-scheduled task instead, eg

ScheduledExecutorService dataTimer = Executors.newScheduledThreadPool(1);

if(isDynamic)
{
    dataTimer.scheduleAtFixedRate(r, 0L, freq, TimeUnit.MILLISECONDS);
}
else
{
    dataTimer.submit(r);
}

In the latter case, the task will execute just once.