Hi Max,
On 16/11/2011 2:55 PM, Weijun Wang wrote:
I need a precise time, and is currently using java.util.Date, which knows
about milliseconds, but unfortunately the precision is only 10-15
milliseconds on a Windows.
In fact, I don't really need it to be so correct. My requirements are:
1. It's enough correct, say, at least as correct as Date.
2. It's precise in a relative sense, i.e. it changes fast
3. It should be monotonic, i.e. it grows, unless the user adjusts the system
clock
There are only two time source available:
1. The time-of-day clock
This is what Date reports and is also what System.currentTimeMillis reports.
It only has millisecond precision. It's rate of update is dependent on the
OS - for Windows that is typically every 10ms or every 15ms depending on
version.
2. The high resolution time source
This is what System.nanoTime reports. It has nanosecond precision, but again
depending on the OS it's resolution (update rate) will vary. The update rate
should easily be in the tens of microseconds. It should be monotonic
non-decreasing but it is not connected to the time-of-day clock (and so
should not be affected by any changes therein).
I have an old blog entry on this:
http://blogs.oracle.com/dholmes/entry/inside_the_hotspot_vm_clocks
David
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