How to get time delta independently from system time?

I'm writing a simple timer in Java. It has Start and Stop buttons, along with a text view showing how much time has passed since the timer was started.

It's implemented by setting initial time with System.currentTimeMillis() and updating current value each second in a loop.

The problem is that if I change system time while the timer is running, the whole measurement fails. E.g., if I set time back one month, the timer shows ne开发者_开发技巧gative value as currentTimeMillis() now returns less value than initial.

So, how do I calculate time delta which would be independent from the system time? It would be also great to make this solution cross-platform.

Use:

System.nanoTime()

This should do it. It doesn't take the system time into account, and can only be used to measure elapsed time. Which is what you want. You need to divide by 1 million to get the elapsed milliseconds. See also the Javadocs.

System.nanoTime();

From Javadoc:

This method can only be used to measure elapsed time and is not related to any other notion of system or wall-clock time.

Use time web services . for example this or this or this

You can install demon like NTP, system time jumping in any directions has a lot of issues and can lead to quite a lot of other problems.

System.nanoTime() not necessarily depend on the system clock - but it can - just make sure the system time is correctly progressing. Modifying system time is a privileged operation, so it someone does that they shall know better.

Here is a bug 13 years of age regarding the same case: http://bugs.sun.com/view_bug.do?bug_id=4290274

HTH