Scheduled tasks with @Scheduled in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

Understanding fixedRate in @Scheduled

What is the behavior of a method annotated with @Scheduled(fixedRate = 5000) in a Spring Boot application?

Spring Boot

@Scheduled(fixedRate = 5000)
public void task() {
    System.out.println("Task executed");
}

A The method runs continuously without any delay.

B The method runs every 5 seconds, counting from the start of the previous execution.

C The method runs once after 5 seconds delay and then stops.

D The method runs every 5 seconds, counting from the end of the previous execution.

💡 Hint

Think about how fixedRate schedules tasks relative to the start time of the previous run.

The fixedRate attribute schedules the method to run at a fixed interval measured from the start time of the previous execution, regardless of how long the method takes to run.

📝 Syntax

intermediate

Correct usage of cron expression in @Scheduled

Which of the following @Scheduled annotations uses a valid cron expression to run a task every day at 3:30 AM?

A @Scheduled(cron = "0 3 30 * * ?")

B @Scheduled(cron = "30 3 * * *")

C @Scheduled(cron = "0 30 3 * * *")

D @Scheduled(cron = "0 30 3 * * ?")

💡 Hint

Remember the cron format: second, minute, hour, day of month, month, day of week, and optional year.

The correct cron expression for 3:30 AM daily is 0 30 3 * * ?. It means at second 0, minute 30, hour 3, every day, every month, any day of week.

🔧 Debug

advanced

Why does @Scheduled method not run?

Given the following Spring Boot component, why does the scheduled method never execute?

Spring Boot

import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;

@Component
public class MyTask {

    @Scheduled(fixedDelay = 1000)
    public void run() {
        System.out.println("Running task");
    }
}

A The method must be static to be scheduled.

B The fixedDelay value must be in milliseconds, but 1000 is invalid.

C The @EnableScheduling annotation is missing in the configuration.

D The @Component annotation is not enough; @Service is required.

💡 Hint

Check if scheduling is enabled in the Spring Boot application.

Scheduling requires enabling with @EnableScheduling on a configuration class. Without it, @Scheduled methods won't run.

❓ state_output

advanced

Effect of long-running @Scheduled method with fixedRate

Consider a method annotated with @Scheduled(fixedRate = 2000) that takes 5 seconds to complete. What happens when the application runs?

Spring Boot

@Scheduled(fixedRate = 2000)
public void longTask() throws InterruptedException {
    Thread.sleep(5000);
    System.out.println("Task done");
}

A The method executions overlap; a new run starts every 2 seconds even if the previous is still running.

B The method waits for the previous execution to finish before starting the next, so it runs every 5 seconds.

C The method runs only once because the fixedRate is less than the execution time.

D The scheduler throws an exception due to overlapping executions.

💡 Hint

Think about how fixedRate schedules tasks regardless of method duration.

With fixedRate, the scheduler triggers the method every 2 seconds from the start time, so if the method takes longer, executions overlap.

🧠 Conceptual

expert

Choosing between fixedDelay and fixedRate

Which statement best describes the difference between fixedDelay and fixedRate in @Scheduled annotations?

A fixedDelay schedules the next execution after the previous finishes; fixedRate schedules based on start time regardless of duration.

B fixedDelay schedules tasks at fixed intervals ignoring execution time; fixedRate waits for task completion before next run.

C fixedDelay and fixedRate behave identically but fixedDelay is deprecated.

D fixedDelay schedules tasks only once; fixedRate schedules repeated tasks.

💡 Hint

Consider when the next task starts relative to the previous task's start or end.

fixedDelay waits until the previous execution finishes before scheduling the next. fixedRate schedules tasks at fixed intervals from the start time, regardless of how long the task takes.