Java Scheduled Task Execution with ScheduledExecutorService

Java Multithreading: Exercise-13 with Solution

Write a Java program that uses the ScheduledExecutorService interface to schedule tasks for execution at a specified time or with a fixed delay.

Sample Solution:

Java Code:

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

public class ScheduledExecutorExercise {

  public static void main(String[] args) {
    ScheduledExecutorService executor = Executors.newScheduledThreadPool(1);

    // Schedule a task to run after a delay of 2 seconds
    executor.schedule(new Task(), 2, TimeUnit.SECONDS);

    // Schedule a task to run after a delay of 3 seconds and repeat every 5 seconds
    executor.scheduleAtFixedRate(new Task(), 3, 5, TimeUnit.SECONDS);

    // Wait for scheduled tasks to complete
    try {
      Thread.sleep(15000);
    } catch (InterruptedException e) {
      e.printStackTrace();
    }

    // Shutdown the executor
    executor.shutdown();
  }

  static class Task implements Runnable {
    @Override
    public void run() {
      System.out.println("Task executed at: " + new Date());
    }
  }
}

Sample Output:

Task executed at: Wed Jul 15 08:25:12 IST 2020
Task executed at: Wed Jul 15 08:25:13 IST 2020
Task executed at: Wed Jul 15 08:25:18 IST 2020
Task executed at: Wed Jul 15 08:25:23 IST 2020

Explanation:

In the above exercise -

• First, we create a ScheduledExecutorService using Executors.newScheduledThreadPool(1) to create a thread pool with a single worker thread.
• Schedule a task to run after a delay of 2 seconds using the schedule() method. This task is executed only once.
• Next schedule a task to run after a delay of 3 seconds and repeat every 5 seconds using the scheduleAtFixedRate() method. This task is executed repeatedly at a fixed rate.
• To allow scheduled tasks to execute, we use Thread.sleep() to pause the main thread for 15 seconds.
• Finally, we shutdown the executor using the shutdown() method to release its resources.

Flowchart:

Java Code Editor:

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