Timer misbehaves if user changes system clock

Question

Can I write a java 'stopwatch' application that records the time between two events, even if the user changes the system clock in between?

Answer 1

I have implemented a short test program because I discovered that different JVMs (Windows <-> Linux) behaved different.
e.g.: if you change the system clock the nanotimer is stable in Windows but not in Linux. (stable means that the nanotime reports the correct elapsed time no matter if the system clock has changed).
Use the test program to check which version is reliable for you OS and your JVM.
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Date;
import java.util.TimerTask;
public class TimingTest
    public static void checkSleepTest()
        long lastTimestamp = System.currentTimeMillis();
        long lastNano = System.nanoTime();
        System.out.println("Start waiting with Thread.sleep(). Reset the system timestamp.");
        while (true)
            try
                Thread.sleep(5000);
            catch (InterruptedException exp)
                System.err.println(exp);
            long time = System.currentTimeMillis();
            long nano = System.nanoTime();
            Date date = new Date(time);
            long dtime = time - lastTimestamp;
            long dnano = nano - lastNano;
            System.out.println("Timer: " + time + " " + date);
            System.out.println("dMillis: " + dtime / 1000d + " dNanos: " + dnano / 1000000000d);
            lastTimestamp = time;
            lastNano = nano;
    public static void checkWaitTest()
        Object lock = new Object();
        long lastTimestamp = System.currentTimeMillis();
        long lastNano = System.nanoTime();
        System.out.println("Start waiting with Object.wait(). Reset the system timestamp.");
        while (true)
            synchronized (lock)
                try
                    lock.wait(5000);
                catch (InterruptedException exp)
                    System.err.println(exp);
            long time = System.currentTimeMillis();
            long nano = System.nanoTime();
            Date date = new Date(time);
            long dtime = time - lastTimestamp;
            long dnano = nano - lastNano;
            System.out.println("Timer: " + time + " " + date);
            System.out.println("dMillis: " + dtime / 1000d + " dNanos: " + dnano / 1000000000d);
            lastTimestamp = time;
            lastNano = nano;
    public static void startUtilTimerTest()
        java.util.Timer timer = new java.util.Timer();
        TimerTask repeatTask = new TimerTask()
            private long lastTimestamp = System.currentTimeMillis();
            private long lastNano = System.nanoTime();
            @Override
            public void run()
                long time = System.currentTimeMillis();
                long nano = System.nanoTime();
                Date date = new Date(time);
                long dtime = time - lastTimestamp;
                long dnano = nano - lastNano;
                System.out.println("Timer: " + time + " " + date);
                System.out.println("dMillis: " + dtime / 1000d + " dNanos: " + dnano / 1000000000d);
                lastTimestamp = time;
                lastNano = nano;
        timer.scheduleAtFixedRate(repeatTask, 1000, 5000);
        System.out.println("Timer has been started. Reset the system timestamp.");
    public static void startSwingTimerTest()
        ActionListener actionTask = new ActionListener()
            private long lastTimestamp = System.currentTimeMillis();
            private long lastNano = System.nanoTime();
            public void actionPerformed(ActionEvent e)
                long time = System.currentTimeMillis();
                long nano = System.nanoTime();
                Date date = new Date(time);
                long dtime = time - lastTimestamp;
                long dnano = nano - lastNano;
                System.out.println("Timer: " + time + " " + date);
                System.out.println("dMillis: " + dtime / 1000d + " dNanos: " + dnano / 1000000000d);
                lastTimestamp = time;
                lastNano = nano;
        javax.swing.Timer timer = new javax.swing.Timer(5000, actionTask);
        timer.start();
        System.out.println("Timer has been started. Reset the system timestamp.");
        // swing timer is a deamon thread => do something else to prevent the program to exit
        while (true)
            try
                Thread.sleep(5000);
            catch (InterruptedException exp)
    public static void main(String[] args)
        if ("swing".equals(args[0]))
            startSwingTimerTest();
        else if ("util".equals(args[0]))
            startUtilTimerTest();
        else if ("sleep".equals(args[0]))
            checkSleepTest();
        else if ("wait".equals(args[0]))
            checkWaitTest();
        else
            System.err.println(args[0] + " not supported.");
}