Java.util.TimerTask class in Java

TimerTask is an abstract class defined in java.util package. TimerTask class defines a task that can be scheduled to run for just once or for repeated number of time. In order to define a TimerTask object, this class needs to be implemented and the run method need to be overridden. The run method is implicitly invoked when a timer object schedules it to do so. 

Note: An instance of TimerTask class is used to define a task the needs to run periodically. 

Constructors:

• TimerTask(): Creates a new timer task

Declaration:

public abstract class TimerTask
        extends Object
        implements Runnable

Methods:

• cancel(): java.util.TimerTask.cancel() Cancels this timer task 
• Syntax:

public boolean cancel()
Returns:
true if this task is scheduled for one-time execution and
has not yet run, or this task is scheduled for repeated execution. 
Returns false if the task was scheduled for one-time 
execution and has already run, or if the task was never scheduled, 
or if the task was already cancelled.

• run(): java.util.TimerTask.run() The action to be performed by this timer task 
• Syntax:

public abstract void run()
Description:
The action to be performed by this timer task

• scheduledExecutionTime(): java.util.TimerTask.scheduledExecutionTime() Returns the scheduled execution time of the most recent actual execution of this task 
• Syntax:

public long scheduledExecutionTime()
Returns: 
the time at which the most recent execution of this task was 
scheduled to occur, in the format returned by Date.getTime(). 
The return value is undefined if the task has yet to 
commence its first execution

Methods inherited from class java.lang.Object

• clone
• equals
• finalize
• getClass
• hashCode
• notify
• notifyAll
• toString
• wait

Java program to demonstrate usage of TimerTask class

// Java program to demonstrate 
// working of TimerTask class
import java.util.Timer;
import java.util.TimerTask;

class Helper extends TimerTask
{
    public static int i = 0;
    public void run()
    {
        System.out.println("Timer ran" + ++i);
        if(i == 4)
        {
            synchronized(Test.obj)
            {
                Test.obj.notify();
            }
        }
    }
    
}


public class Test
{
    public static Test obj;
    public static void main(String[] args) throws InterruptedException
    {
        obj = new Test();
        
        // creating an instance of timer class
        Timer timer = new Timer();
        
        // creating an instance of task to be scheduled
        TimerTask task = new Helper();
        
        // scheduling the timer instance
        timer.schedule(task, 1000, 3000);
        
        // fetching the scheduled execution time of 
        // the most recent actual execution of the task
        System.out.println(task.scheduledExecutionTime());
        
        synchronized(obj)
        {
            //this thread waits until i reaches 4
            obj.wait();
        }
        
        //canceling the task assigned 
        System.out.println("Cancel the timer task: " + task.cancel());
        
        // at this point timer is still running 
        // without any task assigned to it
    
        // canceling the timer instance created
        timer.cancel();
    }
}

Output:

1495715853591
Timer ran 1
Timer ran 2
Timer ran 3
Timer ran 4
Cancel the timer task: true

Reference:

• Oracle