How to time Java program execution speed?

Long startTime = System. CurrentTimeMillis(); for (int I = 0; I Println("Total execution time: " + endTime-startTime); Hope this helped.

You can make use of System#nanoTime(). Get it before and after the execution and just do the math. It's preferred above System#currentTimeMillis() because it has a better precision.

Depending on the hardware and the platform used, you may otherwise get an incorrect gap in elapsed time. Here with Core2Duo on Windows, between about 0 and ~15ms actually nothing can be calculated. A more advanced tool is a profiler.

The timer on Windows doesn't have a particularly good resolution by default. There is a high-performance timer too, but it's much harder to use even from C and Java doesn't (AFAIK) provide access to that low a level of hackery without a JNI thunk. – Donal Fellows Apr 3 '10 at 22:47 +1 for the profiler link.

– GregS Apr 3 '10 at 23:04 nanoTime() has one problem (at least on Windows); the timestamp is specific to the processor core. I had a program that got a negative execution time because it got the "start" timestamp on one core, and the "stop" timestamp on another core. – gustafc Apr 3 '10 at 23:33.

Be aware that there are some issues where System#nanoTime() cannot be reliably used on multi-core CPU's to record elapsed time ... each core has maintains its own TSC (Time Stamp Counter): this counter is used to obtain the nano time (really it is the number of ticks since the CPU booted). Hence, unless the OS does some TSC time warping to keep the cores in sync, then if a thread gets scheduled on one core when the initial time reading is taken, then switched to a different core, the relative time can sporadically appear to jump backwards and forwards. I observed this some time ago on AMD/Solaris where elapsed times between two timing points were sometimes coming back as either negative values or unexpectedly large positive numbers.

There was a Solaris kernel patch and a BIOS setting required to force the AMD PowerNow! Off, which appeared to solved it. Also, there is (AFAIK) a so-far unfixed bug when using java System#nanoTime() in a VirtualBox environment; causing all sorts of bizarre intermittent threading problems for us as much of the java.util.

Concurrency package relies on nano time. See also: http://stackoverflow.com/questions/510462/is-system-nanotime-completely-useless http://vbox.innotek.de/pipermail/vbox-trac/2010-January/135631.html.

1 for clear explanation for the shortcomings of nanoTime. – Jason Apr 4 '10 at 2:59.

You get the current system time, in milliseconds: final long startTime = System. CurrentTimeMillis(); Then you do what you're going to do: for (int I = 0; I.

BalusC's answer is also correct; it depends on the needed timer resolution, and why you need the timing. – Jonathan Feinberg Apr 3 '10 at 22:29.

For simple stuff, System. CurrentTimeMillis() can work. It's actually so common that my IDE is setup so that upon entering "t0" it generates me the following line: final long t0 = System.

CurrentTimeMillis() But for more complicated things, you'll probably want to use statistical time measurements, like here (scroll down a bit and look at the time measurements expressed including standard deviations etc. ): perf4j.codehaus.org/devguide.html.

1 for pointing out auto-generator code. I use a similar statement all the time, and didn't know about inserting code templates. Just found out how to do that with eclipse, and it will definitely help!

– Jason Apr 4 '10 at 3:01.

Use long startTime=System. CurrentTimeMillis() for start time, at the top of the loop put long endTime= System. CurrentTimeMillis(); outside the end of the loop.

You'll have to subtract the values to get the runtime in milliseconds. If you want time in nanoseconds, check out system.nanoTime().

Public class someClass { public static void main(String args) // your app start point { long start = java.util.Calendar.getInstance().getTime(); ... your stuff ... long end = java.util.Calendar.getInstance().getTime(); System.out. Println("it took this long to complete this stuff: " + (end - start) + "ms"); } }.

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