Basic difference between scheduleAtFixedRate vs scheduleWithFixedDelay

Info

Code simply executes a single thread with fixed initial delay, and fixed interval. using two separate methods scheduleAtFixedRate  and scheduleWithFixedDelay. In first run we have used scheduleAtFixedRate  method, then in second run we will use the scheduleWithFixedDelay method. Inside the run method thread sleep for 6secs

/*
     Author: Raj Kirpalsinh
*/ 

import java.util.Date;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

public class SchedularTest {
private ScheduledExecutorService scheduledExecutorService ;
private WorkerThread scanner = new WorkerThread();

public static void main(String... args) {
new SchedularTest().go();
}

private void go() {

  this.scheduledExecutorService = Executors.newSingleThreadScheduledExecutor();
          scheduledExecutorService.scheduleAtFixedRate(scanner, scanner.getInitialDelay(),             scanner.getIntervalTime(), TimeUnit.SECONDS);

              
     //scheduledExecutorService.scheduleWithFixedDelay(scanner,scanner.getInitialDelay(),      //scanner.getIntervalTime(), TimeUnit.SECONDS);

}

private class WorkerThread implements Runnable { 

public long getInitialDelay() {
return 1;
}

public long getIntervalTime() {
return 2;
}

@Override
public void run() {
System.out.println(new Date());
try {
Thread.sleep(6000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}

Output using scheduleWithFixedDelay

Fri Sep 26 17:00:26 IST 2014

Fri Sep 26 17:00:34 IST 2014

Fri Sep 26 17:00:42 IST 2014

Fri Sep 26 17:00:50 IST 2014

Fri Sep 26 17:00:58 IST 2014

Fri Sep 26 17:01:06 IST 2014

Fri Sep 26 17:01:14 IST 2014

Fri Sep 26 17:01:22 IST 2014

Fri Sep 26 17:01:30 IST 2014

Note : fixedDelay method consumes 

Total Time = 

IntervalTime + Thread Task Completion Time

check the total time between each output line you could understand it easily.

Output using scheduleAtFixedRate

Fri Sep 26 17:03:23 IST 2014

Fri Sep 26 17:03:29 IST 2014

Fri Sep 26 17:03:35 IST 2014

Fri Sep 26 17:03:41 IST 2014

Fri Sep 26 17:03:47 IST 2014

Fri Sep 26 17:03:53 IST 2014

Fri Sep 26 17:03:59 IST 2014

Note : fixedRate method consumes 

Total Time = 

IntervalTime

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