System currentTimeMillis vs new Date vs Calendar getInstance getTime

Question

In Java  what are the performance and resource implications of using  System currentTimeMillis      vs    new Date      vs    Calendar getInstance   getTime     As I understand it  System currentTimeMillis   is the most efficient  However  in most applications  that long value would need to be converted to a Date or some similar object to do anything meaningful to humans

User · Answer

I prefer using the value returned by System currentTimeMillis   for all kinds of calculations and only use Calendar or Date if I need to really display a value that is read by humans  This will also prevent 99  of your daylight-saving-time bugs

User · Answer

Depending on your application  you may want to consider using System nanoTime   instead

User · Answer

Looking at the JDK  innermost constructor for Calendar getInstance   has this   public GregorianCalendar TimeZone zone  Locale aLocale        super zone  aLocale       gdate    BaseCalendar Date  gcal newCalendarDate zone       setTimeInMillis System currentTimeMillis         so it already automatically does what you suggest  Date s default constructor holds this   public Date         this System currentTimeMillis         So there really isn t need to get system time specifically unless you want to do some math with it before creating your Calendar Date object with it  Also I do have to recommend joda-time to use as replacement for Java s own calendar date classes if your purpose is to work with date calculations a lot

User · Answer

System currentTimeMillis   is obviously the fastest because it s only one method call and no garbage collector is required

User · Answer

Looking at the JDK  innermost constructor for Calendar getInstance   has this   public GregorianCalendar TimeZone zone  Locale aLocale        super zone  aLocale       gdate    BaseCalendar Date  gcal newCalendarDate zone       setTimeInMillis System currentTimeMillis         so it already automatically does what you suggest  Date s default constructor holds this   public Date         this System currentTimeMillis         So there really isn t need to get system time specifically unless you want to do some math with it before creating your Calendar Date object with it  Also I do have to recommend joda-time to use as replacement for Java s own calendar date classes if your purpose is to work with date calculations a lot

User · Answer

If you re USING a date then I strongly advise that you use jodatime  http   joda-time sourceforge net   Using System currentTimeMillis   for fields that are dates sounds like a very bad idea because you ll end up with a lot of useless code   Both date and calendar are seriously borked  and Calendar is definitely the worst performer of them all    I d advise you to use System currentTimeMillis   when you are actually operating with milliseconds  for instance like this   long start   System currentTimeMillis             do something      long elapsed   System currentTimeMillis   -start

User · Answer

I prefer using the value returned by System currentTimeMillis   for all kinds of calculations and only use Calendar or Date if I need to really display a value that is read by humans  This will also prevent 99  of your daylight-saving-time bugs

User · Answer

I tried this           long now   System currentTimeMillis            for  int i   0  i  lt  10000000  i                  new Date   getTime                      long result   System currentTimeMillis   - now           System out println  Date        result            now   System currentTimeMillis            for  int i   0  i  lt  10000000  i                  System currentTimeMillis                      result   System currentTimeMillis   - now           System out println  currentTimeMillis        result     And result was   Date    199  currentTimeMillis    3

User · Answer

If you re USING a date then I strongly advise that you use jodatime  http   joda-time sourceforge net   Using System currentTimeMillis   for fields that are dates sounds like a very bad idea because you ll end up with a lot of useless code   Both date and calendar are seriously borked  and Calendar is definitely the worst performer of them all    I d advise you to use System currentTimeMillis   when you are actually operating with milliseconds  for instance like this   long start   System currentTimeMillis             do something      long elapsed   System currentTimeMillis   -start

User · Answer

Depending on your application  you may want to consider using System nanoTime   instead

User · Answer

I prefer using the value returned by System currentTimeMillis   for all kinds of calculations and only use Calendar or Date if I need to really display a value that is read by humans  This will also prevent 99  of your daylight-saving-time bugs

User · Answer

I prefer using the value returned by System currentTimeMillis   for all kinds of calculations and only use Calendar or Date if I need to really display a value that is read by humans  This will also prevent 99  of your daylight-saving-time bugs

User · Answer

Depending on your application  you may want to consider using System nanoTime   instead

User · Answer

If you re USING a date then I strongly advise that you use jodatime  http   joda-time sourceforge net   Using System currentTimeMillis   for fields that are dates sounds like a very bad idea because you ll end up with a lot of useless code   Both date and calendar are seriously borked  and Calendar is definitely the worst performer of them all    I d advise you to use System currentTimeMillis   when you are actually operating with milliseconds  for instance like this   long start   System currentTimeMillis             do something      long elapsed   System currentTimeMillis   -start

User · Answer

System currentTimeMillis   is obviously the most efficient since it does not even create an object  but new Date   is really just a thin wrapper about a long  so it is not far behind  Calendar  on the other hand  is relatively slow and very complex  since it has to deal with the considerably complexity and all the oddities that are inherent to dates and times  leap years  daylight savings  timezones  etc     It s generally a good idea to deal only with long timestamps or Date objects within your application  and only use Calendar when you actually need to perform date time calculations  or to format dates for displaying them to the user  If you have to do a lot of this  using Joda Time is probably a good idea  for the cleaner interface and better performance

User · Answer

On my machine I tried check it  My result    Calendar getInstance   getTime     1000000 times    402ms new Date   getTime      1000000 times    18ms System currentTimeMillis     1000000 times    16ms   Don t forget about GC  if you use Calendar getInstance   or new Date

User · Answer

System currentTimeMillis   is obviously the fastest because it s only one method call and no garbage collector is required

User · Answer

On my machine I tried check it  My result    Calendar getInstance   getTime     1000000 times    402ms new Date   getTime      1000000 times    18ms System currentTimeMillis     1000000 times    16ms   Don t forget about GC  if you use Calendar getInstance   or new Date

User · Answer

System currentTimeMillis   is obviously the most efficient since it does not even create an object  but new Date   is really just a thin wrapper about a long  so it is not far behind  Calendar  on the other hand  is relatively slow and very complex  since it has to deal with the considerably complexity and all the oddities that are inherent to dates and times  leap years  daylight savings  timezones  etc     It s generally a good idea to deal only with long timestamps or Date objects within your application  and only use Calendar when you actually need to perform date time calculations  or to format dates for displaying them to the user  If you have to do a lot of this  using Joda Time is probably a good idea  for the cleaner interface and better performance

User · Answer

Looking at the JDK  innermost constructor for Calendar getInstance   has this   public GregorianCalendar TimeZone zone  Locale aLocale        super zone  aLocale       gdate    BaseCalendar Date  gcal newCalendarDate zone       setTimeInMillis System currentTimeMillis         so it already automatically does what you suggest  Date s default constructor holds this   public Date         this System currentTimeMillis         So there really isn t need to get system time specifically unless you want to do some math with it before creating your Calendar Date object with it  Also I do have to recommend joda-time to use as replacement for Java s own calendar date classes if your purpose is to work with date calculations a lot

User · Answer

Depending on your application  you may want to consider using System nanoTime   instead

User · Answer

System currentTimeMillis   is obviously the most efficient since it does not even create an object  but new Date   is really just a thin wrapper about a long  so it is not far behind  Calendar  on the other hand  is relatively slow and very complex  since it has to deal with the considerably complexity and all the oddities that are inherent to dates and times  leap years  daylight savings  timezones  etc     It s generally a good idea to deal only with long timestamps or Date objects within your application  and only use Calendar when you actually need to perform date time calculations  or to format dates for displaying them to the user  If you have to do a lot of this  using Joda Time is probably a good idea  for the cleaner interface and better performance

User · Answer

Looking at the JDK  innermost constructor for Calendar getInstance   has this   public GregorianCalendar TimeZone zone  Locale aLocale        super zone  aLocale       gdate    BaseCalendar Date  gcal newCalendarDate zone       setTimeInMillis System currentTimeMillis         so it already automatically does what you suggest  Date s default constructor holds this   public Date         this System currentTimeMillis         So there really isn t need to get system time specifically unless you want to do some math with it before creating your Calendar Date object with it  Also I do have to recommend joda-time to use as replacement for Java s own calendar date classes if your purpose is to work with date calculations a lot

User · Answer

I tried this           long now   System currentTimeMillis            for  int i   0  i  lt  10000000  i                  new Date   getTime                      long result   System currentTimeMillis   - now           System out println  Date        result            now   System currentTimeMillis            for  int i   0  i  lt  10000000  i                  System currentTimeMillis                      result   System currentTimeMillis   - now           System out println  currentTimeMillis        result     And result was   Date    199  currentTimeMillis    3

User · Answer

If you re USING a date then I strongly advise that you use jodatime  http   joda-time sourceforge net   Using System currentTimeMillis   for fields that are dates sounds like a very bad idea because you ll end up with a lot of useless code   Both date and calendar are seriously borked  and Calendar is definitely the worst performer of them all    I d advise you to use System currentTimeMillis   when you are actually operating with milliseconds  for instance like this   long start   System currentTimeMillis             do something      long elapsed   System currentTimeMillis   -start

User · Answer

System currentTimeMillis   is obviously the most efficient since it does not even create an object  but new Date   is really just a thin wrapper about a long  so it is not far behind  Calendar  on the other hand  is relatively slow and very complex  since it has to deal with the considerably complexity and all the oddities that are inherent to dates and times  leap years  daylight savings  timezones  etc     It s generally a good idea to deal only with long timestamps or Date objects within your application  and only use Calendar when you actually need to perform date time calculations  or to format dates for displaying them to the user  If you have to do a lot of this  using Joda Time is probably a good idea  for the cleaner interface and better performance

[java] System.currentTimeMillis() vs. new Date() vs. Calendar.getInstance().getTime()

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