How To Fix Java Timer Not Following Delay

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Trail: Essential Java Classes
Lesson: Threads: Doing Two or More Tasks At Once

Using the Timer and TimerTask Classes

This department discusses practical aspects of using timers to schedule tasks. The Timer class in the coffee.util package schedules instances of a grade chosen TimerTask . Reminder.coffee is an example of using a timer to perform a task after a filibuster:
import java.util.Timer; import java.util.TimerTask;  /**  * Simple demo that uses coffee.util.Timer to schedule a task   * to execute in one case five seconds have passed.  */  public course Reminder {     Timer timer;      public Reminder(int seconds) {            timer = new Timer();         timer.schedule(new RemindTask(), seconds*1000); 	}      form RemindTask extends TimerTask {         public void run() {            System.out.println("Time's upwardly!");             timer.cancel(); //Terminate the timer thread         }     }      public static void main(String args[]) {         new Reminder(5);         System.out.println("Task scheduled.");     } }          
When you run the example, you get-go see this:
Job scheduled.          
5 seconds later, you see this:
Fourth dimension's up!          
This elementary plan illustrates the bones parts of implementing and scheduling a chore to be executed by a timer thread.
Implement a custom subclass of TimerTask. The run method contains the lawmaking that performs the job. In this example, the subclass is named RemindTask.

Create a thread by instantiating the Timer class.

Instantiate the timer task object (new RemindTask()).
Schedule the timer chore for execution. This example uses the schedule method, with the timer task as the starting time statement and the delay in milliseconds (5000) as the second argument. Another fashion of scheduling a task is to specify the fourth dimension when the task should execute. For example, the post-obit lawmaking schedules a task for execution at eleven:01 p.1000.:
//Get the Date respective to eleven:01:00 pm today. Calendar calendar = Calendar.getInstance(); calendar.set(Calendar.HOUR_OF_DAY, 23); agenda.set(Calendar.Minute, 1); calendar.set up(Agenda.2d, 0); Date fourth dimension = agenda.getTime();  timer = new Timer(); timer.schedule(new RemindTask(), time);              

Stopping Timer Threads

By default, a program keeps running as long as its timer threads are running. Yous can end a timer thread in four ways.

Invoke cancel on the timer. You can do this from anywhere in the programme, such as from a timer chore's run method.

Brand the timer's thread a "daemon" by creating the timer like this: new Timer(true). If the only threads left in the programme are daemon threads, the program exits.

After all the timer's scheduled tasks have finished executing, remove all references to the Timer object. Eventually, the timer'southward thread will terminate.

Invoke the System.go out method, which makes the entire plan (and all its threads) exit.

The Reminder case uses the first scheme, invoking the cancel method from the timer task's run method. Making the timer thread a daemon wouldn't piece of work, because the program needs to go on running until the timer'south task executes.
Sometimes, timer threads aren't the only threads that tin can foreclose a programme from exiting when expected. For example, if you use the AWT at all — even if merely to brand beeps — the AWT automatically creates a nondaemon thread that keeps the program live. The following modification of Reminder adds beeping, which requires us to as well add together a phone call to the Organisation.go out method to brand the program exit. Significant changes are in highlighted. You can find the source code in ReminderBeep.java .
public class ReminderBeep {     ...     public ReminderBeep(int seconds) {            toolkit = Toolkit.getDefaultToolkit();            timer = new Timer();         timer.schedule(new RemindTask(), seconds*chiliad);     }     grade RemindTask extends TimerTask {         public void run() {             System.out.println("Time'due south up!");            toolkit.beep();             //timer.cancel(); // Non necessary considering                               // we telephone call Organisation.get out             System.get out(0);   // Stops the AWT thread                               // (and everything else)            }     }     ... }          

Performing a Chore Repeatedly

Here�southward an example of using a timer to perform a task once per second.
public class AnnoyingBeep {     Toolkit toolkit;     Timer timer;      public AnnoyingBeep() {         toolkit = Toolkit.getDefaultToolkit();         timer = new Timer();            timer.schedule(new RemindTask(),                        0,        //initial delay                        1*1000);  //subsequent rate            }      class RemindTask extends TimerTask {         int numWarningBeeps = 3;         public void run() {             if (numWarningBeeps > 0) {                 toolkit.beep();                 System.out.println("Beep!");                 numWarningBeeps--;             } else {                 toolkit.beep();                  System.out.println("Time's up!");                 //timer.cancel(); // Not necessary because                                   // we telephone call Organization.go out                 System.go out(0);   // Stops the AWT thread                                    // (and everything else)             }         }     }     ... }          
You tin can detect the entire programme in AnnoyingBeep.java . When y'all execute it, you see the following output (our comments about timing are shown in italics):
Task scheduled. Beep!       Beep!            //one 2nd subsequently the first beep            Beep!            //one second afterward the 2d beep            Fourth dimension's upwards!            //one second after the third beep          
The AnnoyingBeep program uses a three-statement version of the schedule method to specify that its task should execute once a second, beginning immediately. Here are all the Timer methods you lot can use to schedule repeated executions of tasks:

schedule(TimerTask task, long delay, long period)

schedule(TimerTask job, Date fourth dimension, long menstruum)

scheduleAtFixedRate(TimerTask task, long filibuster, long period)

scheduleAtFixedRate(TimerTask chore, Date firstTime, long period)

When scheduling a task for repeated execution, you should utilize i of the schedule methods when smoothness is important and a scheduleAtFixedRate method when fourth dimension synchronization is more than important. For example, the AnnoyingBeep programme uses the schedule method, which means that the annoying beeps will all be at least 1 2d autonomously. If one beep is late for any reason, all subsequent beeps will be delayed. If we decide that the AnnoyingBeep program should go out exactly 3 seconds after the kickoff beep — even if information technology means that two beeps might occur close together if a beep is delayed for whatever reason — nosotros should utilise the scheduleAtFixedRate method instead.

More Information about Timers

The timer tasks we've shown have been very simple. They do near nothing and refer just to data that either tin can exist safely accessed from multiple threads or is private to the timer task. As long as your timer task uses only API designed to be thread-safe — such as the methods in the Timer form — implementing timers is relatively straightforward. Nevertheless, if your timer implementation depends on shared resources, such as information used by other places in your program, you demand to be careful. Yous tin find out more than subsequently in this chapter in the section Synchronizing Threads.