How to time Java program execution speed

Question

How do you time the execution of a java program  I m not sure what class I should use to do this   I m kinda looking for something like      Some timer starts here for  int i   0  i  lt  length  i           Do something      End timer here  System out println  Total execution time      totalExecutionTime

User · Accepted Answer

final long startTime   System currentTimeMillis    for  int i   0  i  lt  length  i           Do something   final long endTime   System currentTimeMillis     System out println  Total execution time       endTime - startTime

User · Answer

Have a look at System currentTimeMillis

User · Answer

I created a higher order function which takes the code you want to measure in as a lambda   class Utils        public static  lt T gt  T timeIt String msg  Supplier lt T gt  s            long startTime   System nanoTime            T t   s get            long endTime   System nanoTime            System out println msg           endTime - startTime      ns            return t             public static void timeIt String msg  Runnable r           timeIt msg     - gt   r run    return null                Call it like that   Utils timeIt  code 0      - gt          System out println  Hallo          in case you need the result of the lambda int i   Utils timeIt  code 1      - gt          5   5      Output      code 0  180528 ns   code 1  12003 ns   Special thanks to Andy Turner who helped me cut down the redundancy  See here

User · Answer

Using System currentTimeMillis   is the proper way of doing this  But  if you use command line  and you want to time the whole program approximately and quickly  think about   time java App   which allows you not to modify the code and time your App

User · Answer

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

User · Answer

You may also try Perf4J  Its a neat way of doing what you are looking for  and helps in aggregated performance statistics like mean  minimum  maximum  standard deviation and transactions per second over a set time span  An extract from http   perf4j codehaus org devguide html   StopWatch stopWatch   new LoggingStopWatch     try          the code block being timed - this is just a dummy example     long sleepTime    long  Math random     1000L       Thread sleep sleepTime       if  sleepTime  gt  500L            throw new Exception  Throwing exception               stopWatch stop  codeBlock2 success    Sleep time was  lt  500 ms      catch  Exception e        stopWatch stop  codeBlock2 failure    Exception was      e       Output   INFO  start 1230493236109  time 447  tag codeBlock2 success  message Sleep time was  lt  500 ms  INFO  start 1230493236719  time 567  tag codeBlock2 failure  message Exception was  java lang Exception  Throwing exception  INFO  start 1230493237286  time 986  tag codeBlock2 failure  message Exception was  java lang Exception  Throwing exception  INFO  start 1230493238273  time 194  tag codeBlock2 success  message Sleep time was  lt  500 ms  INFO  start 1230493238467  time 463  tag codeBlock2 success  message Sleep time was  lt  500 ms  INFO  start 1230493238930  time 310  tag codeBlock2 success  message Sleep time was  lt  500 ms  INFO  start 1230493239241  time 610  tag codeBlock2 failure  message Exception was  java lang Exception  Throwing exception  INFO  start 1230493239852  time 84  tag codeBlock2 success  message Sleep time was  lt  500 ms  INFO  start 1230493239937  time 30  tag codeBlock2 success  message Sleep time was  lt  500 ms  INFO  start 1230493239968  time 852  tag codeBlock2 failure  message Exception was  java lang Exception  Throwing exception

User · Answer

Using AOP AspectJ and  Loggable annotation from jcabi-aspects you can do it easy and compact    Loggable Loggable DEBUG  public String getSomeResult          return some value     Every call to this method will be sent to SLF4J logging facility with DEBUG logging level  And every log message will include execution time

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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   Is System nanoTime   completely useless   http   vbox innotek de pipermail vbox-trac 2010-January 135631 html

User · Answer

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     http   perf4j codehaus org devguide html

User · Answer

You can use Stopwatch import com google common base Stopwatch   Stopwatch timer   Stopwatch createStarted      lines to be executed System out println  quot Execution time   quot    timer stop

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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  lt  length  i           Do something     Then you see how long it took   final long elapsedTimeMillis   System currentTimeMillis   - startTime

User · Answer

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

User · Answer

public class someClass      public static void main String   args     your app start point             long start   java util Calendar getInstance   getTimeInMillis                your stuff             long end   java util Calendar getInstance   getTimeInMillis           System out println  it took this long to complete this stuff       end - start     ms

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Here are a few ways to find the execution time in Java   1  System nanoTime    long startTime   System nanoTime         your code     long endTime     System nanoTime    long totalTime   endTime - startTime  System out println  Execution time in nanoseconds        totalTime   System out println  Execution time in milliseconds       totalTime   1000000     2  System currentTimeMillis    long startTime   System currentTimeMillis         your code     long endTime   System currentTimeMillis    long totalTime   endTime - startTime  System out println  Execution time in milliseconds        totalTime     3  Instant now    long startTime   Instant now   toEpochMilli         your code     long endTime   Instant now   toEpochMilli    long totalTime   endTime - startTime  System out println  Execution time in milliseconds      totalTime     or  Instant start   Instant now         your code     Instant end   Instant now    Duration interval   Duration between start  end   System out println  Execution time in seconds     interval getSeconds       4  Date getTime    long startTime   new Date   getTime         your code     long endTime   new Date   getTime    long totalTime   endTime - startTime  System out println  Execution time in milliseconds      totalTime

[java] How to time Java program execution speed

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