Java.util.Timer Class in Java (original) (raw)

Last Updated : 14 Nov, 2021

Timer class provides a method call that is used by a thread to schedule a task, such as running a block of code after some regular instant of time. Each task may be scheduled to run once or for a repeated number of executions. Each timer object is associated with a background thread that is responsible for the execution of all the tasks of a timer object.
Note:

Constructors:

Declaration:

public class Timer extends Object

Methods inherited from class java.lang.Object

Methods:

public void cancel()

public int purge() Returns: the number of tasks removed from the queue

public void schedule(TimerTask task, Date time) Parameters: task - task to be scheduled. time - time at which task is to be executed. Throws: IllegalArgumentException - if time.getTime() is negative. IllegalStateException - if the task was already scheduled or cancelled, the timer was cancelled, or timer thread terminated. NullPointerException - if task or time is null

public void schedule(TimerTask task, Date firstTime, long period) Parameters: task - task to be scheduled. firstTime - First time at which task is to be executed. period - time in milliseconds between successive task executions. Throws: IllegalArgumentException - if firstTime.getTime() < 0, or period <= 0 IllegalStateException - if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated. NullPointerException - if task or firstTime is null

Java `

// Java program to demonstrate //schedule method calls of Timer 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); } }

public class Test { public static void main(String[] args) {

    Timer timer = new Timer();
    TimerTask task = new Helper();
    
    timer.schedule(task, 2000, 5000);
    
}

}

`

Output:

Timer ran 1 Timer ran 2 Timer ran 3 Timer ran 4 Timer ran 5 . . .

public void schedule(TimerTask task, long delay) Parameters: task - task to be scheduled. delay - delay in milliseconds before task is to be executed. Throws: IllegalArgumentException - if delay is negative, or delay + System.currentTimeMillis() is negative. IllegalStateException - if a task was already scheduled or cancelled, the timer was cancelled, or timer thread terminated. NullPointerException - if task is null

public void schedule(TimerTask task, long delay, long period) Parameters: task - task to be scheduled. delay - delay in milliseconds before task is to be executed. period - time in milliseconds between successive task executions. Throws: IllegalArgumentException - if delay < 0, or delay + System.currentTimeMillis() < 0, or period <= 0 IllegalStateException - if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated. NullPointerException - if task is null

public void scheduleAtFixedRate(TimerTask task, Date firstTime, long period) Parameters: task - task to be scheduled. firstTime - First time at which task is to be executed. period - time in milliseconds between successive task executions. Throws: IllegalArgumentException - if firstTime.getTime() < 0 or period <= 0 IllegalStateException - if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated. NullPointerException - if task or firstTime is null

public void scheduleAtFixedRate(TimerTask task, long delay, long period) Parameters: task - task to be scheduled. delay - delay in milliseconds before task is to be executed. period - time in milliseconds between successive task executions. Throws: IllegalArgumentException - if delay < 0, or delay + System.currentTimeMillis() < 0, or period <= 0 IllegalStateException - if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated. NullPointerException - if task is null

Java `

// Java program to demonstrate // scheduleAtFixedRate method of Timer class

import java.util.Timer; import java.util.TimerTask; import java.util.*;

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 { protected static Test obj; public static void main(String[] args) throws InterruptedException { obj = new Test();

    //creating a new instance of timer class
    Timer timer = new Timer();
    TimerTask task = new Helper();

    //instance of date object for fixed-rate execution
    Date date = new Date();

    timer.scheduleAtFixedRate(task, date, 5000);
    
    System.out.println("Timer running");
    synchronized(obj)
    {
        //make the main thread wait
        obj.wait();
        
        //once timer has scheduled the task 4 times, 
        //main thread resumes
        //and terminates the timer
        timer.cancel();
        
        //purge is used to remove all cancelled 
        //tasks from the timer'stack queue
        System.out.println(timer.purge());
    }
}

}

`

Output:

Timer running Timer ran 1 Timer ran 2 Timer ran 3 Timer ran 4 0

Reference: