Timer scheduleAtFixedRate(TimerTask, Date, long) in Java

scheduleAtFixedRate(TimerTask, Date, long): This method is available in java.util.Timer class of Java.

Syntax:

void java.util.Timer.scheduleAtFixedRate(TimerTask task, Date firstTime, long period)

This method takes three arguments. This method schedules the specified task for repeated fixed-rate execution, beginning at the specified time.

Note: Subsequent executions take place at approximately regular intervals, separated by the specified period.

Parameters: Three parameters are required for this method.

task: task to be scheduled.

firstTime: First time at which task is to be executed.

period: time in milliseconds between successive task executions.

Throws:

1. IllegalArgumentException - if firstTime.getTime() < 0 or period <= 0.

2. IllegalStateException - if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated.

3. NullPointerException - if task or firstTime is null

Approach 1: When no exception

Java

import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;

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

        Timer timer = new Timer();

        TimerTask task = new TimerTask() {

            @Override
            public void run() {
                System.out.println("Runner");

            }
        };
        Date firtTime = new Date();
        long period = 10000L;
        timer.scheduleAtFixedRate(task, firtTime, period);

    }
}

Output:

Runner
Runner
.....

Approach 2: IllegalArgumentException

Java

import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;

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

        Timer timer = new Timer();

        TimerTask task = new TimerTask() {

            @Override
            public void run() {
                System.out.println("Runner");

            }
        };
        Date firtTime = new Date();
        firtTime.setTime(-1000L);
        long period = 10000L;
        timer.scheduleAtFixedRate(task, firtTime, period);

    }
}

Output:

Exception in thread "main" java.lang.IllegalArgumentException: Illegal execution time.
	at java.base/java.util.Timer.sched(Timer.java:389)
	at java.base/java.util.Timer.scheduleAtFixedRate(Timer.java:371)
	

Approach 3: IllegalStateException

Java

import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;

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

        Timer timer = new Timer();

        TimerTask task = new TimerTask() {

            @Override
            public void run() {
                System.out.println("Runner");

            }
        };
        Date firtTime = new Date();
        long period = 10000L;
        timer.cancel();
        timer.scheduleAtFixedRate(task, firtTime, period);

    }
}

Output:

Exception in thread "main" java.lang.IllegalStateException: Timer already cancelled.
	at java.base/java.util.Timer.sched(Timer.java:398)
	at java.base/java.util.Timer.scheduleAtFixedRate(Timer.java:371)
	

Approach 4: NullPointerException 

Java

import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;

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

        Timer timer = new Timer();

        TimerTask task = new TimerTask() {

            @Override
            public void run() {
                System.out.println("Runner");

            }
        };
        Date firtTime = null;
        long period = 10000L;
        timer.scheduleAtFixedRate(task, firtTime, period);

    }
}

Output:

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "java.util.Date.getTime()" because "firstTime" is null
	at java.base/java.util.Timer.scheduleAtFixedRate(Timer.java:371)