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 difference, measured in nanoseconds, between the current time and midnight, January 1, 1970 UTC. The function returns long value.
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.
What is the difference between currenttimemillis and 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. Returns the current value of the most precise available system timer, in nanoseconds.
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.
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What is System nanoTime ()?
nanoTime() method returns the current value of the most precise available system timer, in nanoseconds. The value returned represents nanoseconds since some fixed but arbitrary time (in the future, so values may be negative) and provides nanosecond precision, but not necessarily nanosecond accuracy.
Is System nanoTime thread safe?
It is thread safe.
Is System nanoTime () reliable?
nanoTime() is a great function, but one thing it's not: accurate to the nanosecond. The accuracy of your measurement varies widely depending on your operation system, on your hardware and on your Java version. As a rule of thumb, you can expect microsecond resolution (and a lot better on some systems).
How Fast Is System nanoTime?
System. currentTimeMillis() takes about 29 nanoseconds per call while System. nanoTime() takes about 25 nanoseconds.
Is system nanoTime unique?
nanoTime() will return a unique value.
Is nanoTime monotonic?
In comparison, System. nanoTime() is monotonic so we should have used this one.
What is one nano second?
A nanosecond (ns or nsec) is one billionth (10-9) of a second and is a common measurement of read or write access time to random access memory (RAM). Admiral Grace Hopper famously handed out foot-long lengths of wire to students to illustrate how far an electrical signal can travel in a nanosecond.
Is nanoseconds and milliseconds the same?
Nanosecond is one billionth of a second. Microsecond is one millionth of a second. Millisecond is one thousandth of a second.
How do you calculate nanoseconds in Java?
Time is measured in nanoseconds by using the method nanoTime() method. This method returns the current value of the most precise system timer available in nanoseconds. It is used for measuring elapsed time. long startTime = System.
How do you convert milliseconds to nanoseconds in Java?
The time in nanoseconds is equal to the milliseconds multiplied by 1,000,000.
Is system currentTimeMillis accurate?
currentTimeMillis() actually give the time accurate to the nearest millisecond on Linux, Mac OS and Windows (and since which versions - I know, for example, that Windows only used to be accurate to the nearest 15/16 milliseconds).
What is System currentTimeMillis?
currentTimeMillis() method returns the current time in milliseconds. 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.
Is nanoseconds and milliseconds the same?
Nanosecond is one billionth of a second. Microsecond is one millionth of a second. Millisecond is one thousandth of a second.
What is one nano second?
A nanosecond (ns or nsec) is one billionth (10-9) of a second and is a common measurement of read or write access time to random access memory (RAM). Admiral Grace Hopper famously handed out foot-long lengths of wire to students to illustrate how far an electrical signal can travel in a nanosecond.
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.
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.
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:
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 is Java RTS?
With Java RTS, all time-based APIs (for example, Timers, Periodic Threads, Deadline Monitoring, and so forth) are based on the high-resolution timer. And, together with real-time priorities, they can ensure that the appropriate code will be executed at the right time for real-time constraints. In contrast, ordinary Java SE APIs offer just a few methods capable of handling high-resolution times, with no guarantee of execution at a given time. Using System.nanoTime () between various points in the code to perform elapsed time measurements should always be accurate.
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.
How many nanoseconds is XP?
On my XP systems, I see system time reported to at least 100 microseconds 278 nanoseconds using the following code:
Is nanotime available for Windows?
I've had good experience with nanotime. It provides wall-clock time as two longs (seconds since the epoch and nanoseconds within that second), using a JNI library. It's available with the JNI part precompiled for both Windows and Linux.
Is System.currentTimeMillis safe?
System.currentTimeMillis () is not safe for elapsed time because this method is sensitive to the system realtime clock changes of the system. You should use System.nanoTime . Please refer to Java System help: About nanoTime method: ..
Is nanotime immune to disruption?
But don't underestimate the disruption due to internet time sync, or perhaps remote desktop users. The nanoTime API is immune to this kind of disruption.
Does nanotime have a performance cost?
As other answers suggest, nanoTime does have a performance cost if called repeatedly -- it would be best to call it just once per frame, and use the same value to calculate the entire frame.
