How do I measure time elapsed in Java? [duplicate]

by

Unfortunately, none of the ten answers posted so far are quite right.

If you are measuring elapsed time, and you want it to be correct, you must use System.nanoTime(). You cannot use System.currentTimeMillis(), unless you don’t mind your result being wrong.

The purpose of nanoTime is to measure elapsed time, and the purpose of currentTimeMillis is to measure wall-clock time. You can’t use the one for the other purpose. The reason is that no computer’s clock is perfect; it always drifts and occasionally needs to be corrected. This correction might either happen manually, or in the case of most machines, there’s a process that runs and continually issues small corrections to the system clock (“wall clock”). These tend to happen often. Another such correction happens whenever there is a leap second.

Since nanoTime‘s purpose is to measure elapsed time, it is unaffected by any of these small corrections. It is what you want to use. Any timings currently underway with currentTimeMillis will be off — possibly even negative.

You may say, “this doesn’t sound like it would ever really matter that much,” to which I say, maybe not, but overall, isn’t correct code just better than incorrect code? Besides, nanoTime is shorter to type anyway.

Previously posted disclaimers about nanoTime usually having only microsecond precision are valid. Also it can take more than a whole microsecond to invoke, depending on circumstances (as can the other one), so don’t expect to time very very small intervals correctly.

More Related Contents:

  1. Sort Arraylist With Times [duplicate]
  2. Java string to date conversion
  3. How to convert Milliseconds to “X mins, x seconds” in Java?
  4. What is this date format? 2011-08-12T20:17:46.384Z
  5. How to calculate “time ago” in Java?
  6. Convert timestamp in milliseconds to string formatted time in Java
  7. Time comparison
  8. Should I use Java date and time classes or go with a 3rd party library like Joda Time?
  9. JFormattedTextField : input time duration value
  10. Creating java date object from year,month,day
  11. Best way to constrain user to enter a time in a JTextField
  12. System.currentTimeMillis() vs. new Date() vs. Calendar.getInstance().getTime()
  13. Java Date cut off time information
  14. Conversion from 12 hours time to 24 hours time in java
  15. Java code for getting current time [duplicate]
  16. Convert java.time.Instant to java.sql.Timestamp without Zone offset
  17. Calculate Difference between two times in Android
  18. How to properly format the date?
  19. How do you have the code pause for a couple of seconds in android?
  20. How to stop execution after a certain time in Java?
  21. How to convert HH:mm:ss.SSS to milliseconds?
  22. Parsing time strings like “1h 30min”
  23. I want to get current time in Java but without the Internet and without the system time
  24. java.lang.System.currentTimeMillis() replace method
  25. Getting the current time millis from device and converting it into a new date with different timezone [duplicate]
  26. DateTimeParse Exception
  27. Getting Date in HTTP format in Java
  28. Get the number of days, weeks, and months, since Epoch in Java
  29. How can I measure time with microsecond precision in Java?
  30. print current date in java

Leave a Comment