CODEWITHSUNDEEP
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Freewind
Freewind

Reputation: 198188

System.currentTimeMillis() is not accurate on windows XP?

It seems System.currentTimeMillis is not very accurate.

See this sample:

public class MillisTime {
    public static void main(String[] args) {
        long start = 0;
        long end = 0;
        while (true) {
            if (start == 0) {
                start = System.currentTimeMillis();
            } else {
                long current = System.currentTimeMillis();
                if (current != start) {
                    end = current;
                    break;
                }
            }
        }
        System.out.println("The time interval of your OS: " + (end - start) + "ms");
    }
}

The result is (on Windows XP):

The time interval of your OS: 15ms

Why it's not 1ms? And how to get accurate millis second of current time?

Upvotes: 1

Views: 3022

Answers (3)

JB Nizet
JB Nizet

Reputation: 691635

Yes. The javadoc for System.currentTimeMillis() says it:

Returns the current time in milliseconds. Note that while the unit of time of the return value is a millisecond, the granularity of the value depends on the underlying operating system and may be larger. For example, many operating systems measure time in units of tens of milliseconds.

You could use System.nanoTime(), but make sure to read its javadoc to understand its limitations.

Upvotes: 2

Brett Walker
Brett Walker

Reputation: 3576

It is not possible to get any more accurate with java on windows.

Upvotes: 1

Jon Skeet
Jon Skeet

Reputation: 1499790

This is entirely expected. You'd see the same thing on .NET using DateTime.Now. (See Eric Lippert's blog post on the topic for a .NET-oriented view on this same topic.)

You can use System.nanoTime() to get a more accurate timer for measurements only - that's not meant to give an absolute time, it's only for measuring intervals.

I don't know of any way to get a more accurate absolute time, either from Java or from Win32. To be honest, how accurate is the system clock going to be anyway? Even with regular syncing with an NTP server I'd expect at least a few milliseconds inaccuracy.

Basically, if you're relying on getting an absolute time really accurately, you should probably change your design.

Upvotes: 8

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