System.nanoTime () returns the current value of the most precise available system timer in nanoseconds. The value returned represents nanoseconds passed since some fixed but arbitrary time. System.nanoTime () has nothing to do with dates and time-of-day. System.nanoTime () is an ongoing count of passing nanoseconds, nothing more.
What is system nanotime() in Java?
In this tutorial, we will learn about the Java System.nanoTime () function, and learn how to use this function to the current time in nanoseconds, with the help of examples. System.nanoTime () returns the current value of the running Java Virtual Machine’s high-resolution time source, in nanoseconds.
What is the value returned by nanotime()?
The value returned by nanoTime () is the difference, measured in nanoseconds, between the current time and midnight, January 1, 1970 UTC. The function returns long value. In this example, we will get the current time in the resolution of nanoseconds using System.nanoTime () method.
When to use system nanotime() instead of milli seconds?
Time taken in nano seconds: 2519657 Time taken in milli seconds: 3 In conclusion, System.nanoTime () can/must be used whenever tasks of high precisions are to be performed, because it might seem that milli seconds is enough precision but for applications requiring fast performances (like games) nanoTime () will give much better results.
What is the use of nano time in Java?
Java.lang.System.nanoTime() Method. Description. The java.lang.System.nanoTime() method returns the current value of the most precise available system timer, in nanoseconds.
Why should nanotime be used?
When to use nanotime?
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java - System.currentTimeMillis vs System.nanoTime - Stack Overflow
If you're just looking for extremely precise measurements of elapsed time, use System.nanoTime().System.currentTimeMillis() will give you the most accurate possible elapsed time in milliseconds since the epoch, but System.nanoTime() gives you a nanosecond-precise time, relative to some arbitrary point. From the Java Documentation: public static long nanoTime()
Is System.nanoTime() completely useless? - Stack Overflow
As documented in the blog post Beware of System.nanoTime() in Java, on x86 systems, Java's System.nanoTime() returns the time value using a CPU specific counter. Now consider the following case I use to measure time of a call: long time1= System.nanoTime(); foo(); long time2 = System.nanoTime(); long timeSpent = time2-time1;
Java System.nanoTime and System.currentTimeMillis - CodeVsColor
In this tutorial, we will learn two most commonly used Java System functions - System.nanoTime and System.currentTimeMillis(). Both are time related functions, i.e. to get a time from the system (not the current time ).
Java - How to convert System.nanoTime to Seconds - Mkyong.com
We can just divide the nanoTime by 1_000_000_000, or use the TimeUnit.SECONDS.convert to convert it.
Java System currentTimeMillis() Method - Javatpoint
Java System currentTimeMillis() Method with Examples on arrayCopy(), clearProperty(), console(), currentTimeMillis(), getenv(), setErr(), setOut(), runFinalization() etc.
Java System.nanoTime() - Syntax & Examples - TutorialKart
Java System.nanoTime() – Examples In this tutorial, we will learn about the Java System.nanoTime() function, and learn how to use this function to the current time in nanoseconds, with the help of examples. nanoTime() System.nanoTime() returns the current value of the running Java Virtual Machine’s high-resolution time source, in nanoseconds. The value returned by nanoTime() is the ...
Example 1 – nanoTime ()
In this example, we will get the current time in the resolution of nanoseconds using System.nanoTime () method.
Example 2 – nanoTime () – Difference
In this example, we will calculate the time taken by an empty for loop to iterate one thousand times, using System.nanoTime () method. We will capture the current time before and after the for loop. And the difference between the values returned by nanoTime () will give the execution time of this for loop in nanoseconds.
Conclusion
In this Java Tutorial, we have learnt the syntax of Java System.nanoTime () function, and also learnt how to use this function with the help of examples.
Why should nanotime be used?
From the first look it might seem that nanoTime () should be used because it gives more precise value of time (in nano seconds, compared to milli seconds that the other method returns). But is it always efficient on the CPU to use nanoTime? Let us look at pros and cons of using both the methods:
When to use nanotime?
In conclusion, System.nanoTime () can/must be used whenever tasks of high precisions are to be performed, because it might seem that milli seconds is enough precision but for applications requiring fast performances (like games) nanoTime () will give much better results.
What is system.nanotime in Java?
As documented in the blog post Beware of System.nanoTime () in Java, on x86 systems, Java's System.nanoTime () returns the time value using a CPU specific counter. Now consider the following case I use to measure time of a call:
What is the Java nanotime method?
Java also has a caveat for the nanoTime () method: This method can only be used to measure elapsed time and is not related to any other notion of system or wall-clock time.
What happens after measuring time1?
Now in a multi-core system, it could be that after measuring time1, the thread is scheduled to a different processor whose counter is less than that of the previous CPU. Thus we could get a value in time2 which is less than time1. Thus we would get a negative value in timeSpent.
Is nanotime safe?
That post is wrong, and nanoTime is safe. There's a comment on the post which links to a blog post by David Holmes, a realtime and concurrency guy at Sun. It says:
Is nanotime better than currenttimemillis?
Nonetheless, nanoTime () should still be preferred for implementing timed blocking, interval waiting, timeouts, etc. to currentTimeMillis () because the latter is a subject to the "time going backward" phenomenon (e. g. due to server time correction), i. e. currentTimeMillis () is not suitable for measuring time intervals at all. See this answer for more information.
Is elapsed nanos negative?
and variable 'elapsedNanos' had a negative value. (I'm positive that the intermediate call took less than 293 years as well, which is the overflow point for nanos stored in longs :)
Does changing system time affect nanotime?
I know that changing the system time doesn't affect nanotime. That is not the problem I describe above. The problem is that each CPU will keep a different counter since it was turned on. This counter can be lower on the second CPU compared to the first CPU. Since the thread can be scheduled by the OS to the second CPU after getting time1, the value of timeSpent may be incorrect and even negative.
Preface
Benchmarking business is hard, no surprises there. Most of the time benchmarking involves measuring time, and it is remarkable how many people believe time is very simple to measure. Better yet, most people believe that asking system for time is dirt cheap, and can be used to measure just about any effect one could want to measure.
Building Performance Models
These days I find myself telling people that benchmark numbers don’t matter on their own. It’s important what models you derive from those numbers.
Omission Considerations
Gil Tene likes to talk about Coordinated Omission in the context of measuring the latency. We will direct interested readers there. In this section, we would like to talk about Omission in the context of measuring the throughput.
Steady State Considerations
We started this post with seemingly irrelevant part about volatile writes, and let us conclude with seemingly irrelevant part about Fibonacci. You will see how far-fetching the implications from the previous sections are.
Conclusions
System.nanoTime is as bad as String.intern now: you can use it, but use it wisely. The latency, granularity, and scalability effects introduced by timers may and will affect your measurements if done without proper rigor.
Why should nanotime be used?
From the first look it might seem that nanoTime () should be used because it gives more precise value of time (in nano seconds, compared to milli seconds that the other method returns). But is it always efficient on the CPU to use nanoTime? Let us look at pros and cons of using both the methods:
When to use nanotime?
In conclusion, System.nanoTime () can/must be used whenever tasks of high precisions are to be performed, because it might seem that milli seconds is enough precision but for applications requiring fast performances (like games) nanoTime () will give much better results.