Java ScheduledExecutorService examples

In Java, we can use ScheduledExecutorService to run a task periodically or once time after a predefined delay by TimeUnit.

1. Run a Task Once

The ScheduledExecutorService accepts both Runnable and Callable tasks.

1.1 Run a Runnable task after 5 seconds initial delay.

package com.mkyong.concurrency.executor.scheduler;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
public class ScheduledExecutorRunnable {
    public static void main(String[] args) {
        ScheduledExecutorService ses = Executors.newScheduledThreadPool(1);
        Runnable task2 = () -> System.out.println("Running task2...");
        task1();
        //run this task after 5 seconds, nonblock for task3
        ses.schedule(task2, 5, TimeUnit.SECONDS);
        task3();
        ses.shutdown();
    public static void task1() {
        System.out.println("Running task1...");
    public static void task3() {
        System.out.println("Running task3...");

Output

Running task1...
Running task3...
Running task2... //display after 5 seconds

1.2 Run a Callable task after 5 seconds initial delay.

package com.mkyong.concurrency.executor.scheduler;
import java.util.concurrent.*;
public class ScheduledExecutorCallable {
    public static void main(String[] args) throws InterruptedException, ExecutionException {
        ScheduledExecutorService ses = Executors.newScheduledThreadPool(1);
        Callable<Integer> task2 = () -> 10;
        task1();
        //run this task after 5 seconds, nonblock for task3, returns a future
        ScheduledFuture<Integer> schedule = ses.schedule(task2, 5, TimeUnit.SECONDS);
        task3();
        // block and get the result
        System.out.println(schedule.get());
        System.out.println("shutdown!");
        ses.shutdown();
    public static void task1() {
        System.out.println("Running task1...");
    public static void task3() {
        System.out.println("Running task3...");

Output

Running task1...
Running task3...
10					//display after 5 seconds
shutdown!

2. Run a Task Periodically

To run a task periodically, uses scheduleAtFixedRate

2.1 Run a Runnable task every 1 second, after 5 seconds initial delay.

package com.mkyong.concurrency.executor.scheduler;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;
public class ScheduledExecutorRepeat {
    private static int count = 0;
    public static void main(String[] args) throws InterruptedException {
        ScheduledExecutorService ses = Executors.newScheduledThreadPool(1);
        Runnable task1 = () -> {
            count++;
            System.out.println("Running...task1 - count : " + count);
        };
        // init Delay = 5, repeat the task every 1 second
        ScheduledFuture<?> scheduledFuture = ses.scheduleAtFixedRate(task1, 5, 1, TimeUnit.SECONDS);
        while (true) {
            System.out.println("count :" + count);
            Thread.sleep(1000);
            if (count == 5) {
                System.out.println("Count is 5, cancel the scheduledFuture!");
                scheduledFuture.cancel(true);
                ses.shutdown();
                break;

Output

count :0
count :0
count :0
count :0
count :0
Running...task1 - count : 1
count :1
Running...task1 - count : 2
count :2
Running...task1 - count : 3
count :3
Running...task1 - count : 4
count :4
Running...task1 - count : 5
Count is 5, cancel the scheduledFuture!

References

1. ScheduledExecutorService JavaDoc