Languages

Implementing Timer Tasks in Java

Java programming language provides a class utility known as Timer Task. It allows one to schedule different tasks.  In other words, a task can be executed after a given period or at a specified date and time.

A Timer in Java is a process that enables threads to schedule tasks for later execution.

Scheduling is done by keeping a specific process in the queue such that when the execution time comes, the processor can suspend other processes and run the task.

Prerequisites
Java timer task methods
Code example
Conclusion

Prerequisites

To understand this article better you will need to:

Have a basic understanding of Java
Have a code editor such as Intellij Idea.

Java Timer task methods

There are three Java Timer Task Methods:

cancel() method
run() method
ScheduleExecutionTimer

Cancel() method

This method cancels a scheduled task in Java. It means that no task will be executed in a particular period.

Run() method

The run() method is responsible for running the scheduled task.

ScheduleExecutionTime() Method

This method returns the scheduled execution time for the latest task in memory.

Code example

When you have finished downloading IntelliJ IDEA, run it as administrator and then follow the prompts on the screen to finish setting it up.

After installing the IDE, launch it and click on New Project, as shown in the figure below:

New

Select java then click Next:

Java

Check the Create project from template and click Next:

Project template

On the next screen, enter the project name as TimerTask and click Finish. We will be able to write our code on the next screen. The environment should look like this:

Enviroment

Let's create an example that schedules a task and displays the message Happy Birthday John Doe when the date is October 30th, 2021 at midnight.

package com.company;
import java.util.Calendar;
import java.util.Timer;
import java.util.TimerTask;
public class Main {
    public static void main(String[] args) {
        Timer T = new Timer();
        TimerTask Birthday = new TimerTask(){
            @Override
            public void run(){
                System.out.println("Happy Birthday John Doe");
            }
        };
        Calendar date = Calendar.getInstance();
        date.set(2021, Calendar.OCTOBER, 31, 0, 0, 0);
        T.schedule(Birthday, date.getTime());
    }
}

The output of the above code will be:

Happy Birthday John Doe

In the above code, we are importing the Calendar, Timer, and TimerTask utilities.

Timer T = new Timer() is the instance of a timer that keeps track of time. Birthday is the task to be executed by the TimerTask.

When the time is up, the run function of the TimerTask instance is executed.

The schedule function links the task to the timer. This method references the task that will be executed.

In the following example, we will create an instance of Calendar Date and set the YEAR, MONTH, DAY, HOUR, MINUTE, and SECOND that the task will be executed.

We can also include a count-down timer in the project so that our timer starts counting before the task executes.

This can be achieved using if statements and decrement operators as shown below:

package com.company;
import java.util.Calendar;
import java.util.Timer;
import java.util.TimerTask;
public class Main {
    public static void main(String[] args) {
        Timer T = new Timer();
        TimerTask Birthday = new TimerTask(){
            int i = 5;
            @Override
            public void run(){
                if(i>0){
                    System.out.println(i);
                    i--;
                }
                else{
                    System.out.println("Happy Birthday John Doe");
                    T.cancel();
                }
            }
        };
        Calendar date = Calendar.getInstance();
        date.set(2021, Calendar.OCTOBER, 30,23, 59, 54);
       T.scheduleAtFixedRate(Birthday, date.getTime(), 1000);
    }
}

The output of the code now is shown below:

55
56
57
58
59
Happy Birthday John Doe

To enable the counter to count at a rate of 1 second, we are using T.scheduleAtFixedRate (Birthday, date.getTime(), 1000); instead of T.schedule(Birthday, date.getTime());. 1000 milliseconds represents the count period.

The variable i is initialized to 5. This implies that the task will be executed after five seconds.

The time OCTOBER, 30,23, 59, 54 indicates that the counter will begin on October 30<sup>th</sup>, at 23:59 hours, and at the 54<sup>th</sup> second.

The cancel() method is used to cancel the execution of the task to prevent it from being executed again once the task is completed.