Calculating the difference between two Java date instances

Question

I m using Java s java util Date class in Scala and want to compare a Date object and the current time  I know I can calculate the delta by using getTime      new java util Date    getTime   - oldDate getTime     However  this just leaves me with a long representing milliseconds  Is there any simpler  nicer way to get a time delta

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try this    int epoch    int   new java text SimpleDateFormat  MM dd yyyy HH mm ss   parse  01 01 1970  00 00 00   getTime     1000     you can edit the string in the parse   methods param

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Days d   Days daysBetween startDate  endDate   int days   d getDays      https   www joda org joda-time faq html datediff

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Using millisecond approach can cause problems in some locales   Lets take  for example  the difference between the two dates 03 24 2007 and 03 25 2007 should be 1 day    However  using the millisecond route  you ll get 0 days  if you run this in the UK        Manual Method - YIELDS INCORRECT RESULTS - DO NOT USE         This method is used to find the no of days between the given dates      public long calculateDays Date dateEarly  Date dateLater         return  dateLater getTime   - dateEarly getTime       24   60   60   1000          Better way to implement this is to use java util Calendar      Using Calendar - THE CORRECT WAY      public static long daysBetween Calendar startDate  Calendar endDate        Calendar date    Calendar  startDate clone        long daysBetween   0      while  date before endDate           date add Calendar DAY OF MONTH  1         daysBetween              return daysBetween

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Another pure Java variation   public boolean isWithin30Days Calendar queryCalendar            1  Take the date you are checking  and roll it back N days     Calendar queryCalMinus30Days   Calendar getInstance        queryCalMinus30Days setTime queryCalendar getTime         queryCalMinus30Days add Calendar DATE  -30      subtract 30 days from the calendar         2  Get respective milliseconds for the two Calendars  now  amp  queryCal minus N days      long nowL   Calendar getInstance   getTimeInMillis        long queryCalMinus30DaysL   queryCalMinus30Days getTimeInMillis            3  if nowL is still less than the queryCalMinus30DaysL  it means queryCalendar is more than 30 days into future     boolean isWithin30Days   nowL  gt   queryCalMinus30DaysL       return isWithin30Days      thanks to starter code here  https   stackoverflow com a 30207726 2162226

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Michael Borgwardt s answer actually does not work correctly in Android  Rounding errors exist  Example 19th to 21st May says 1 day because it casts 1 99 to 1  Use round before casting to int    Fix  int diffInDays    int Math round    newerDate getTime   - olderDate getTime                         1000   60   60   24       Note that this works with UTC dates  so the difference may be a day off if you look at local dates  And getting it to work correctly with local dates requires a completely different approach due to daylight savings time

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If you don t want to use JodaTime or similar  the best solution is probably this   final static long MILLIS PER DAY   24   3600   1000  long msDiff  date1 getTime   - date2 getTime    long daysDiff   Math round msDiff     double MILLIS PER DAY      The number of ms per day is not always the same  because of daylight saving time and leap seconds   but it s very close  and at least deviations due to daylight saving time cancel out over longer periods  Therefore dividing and then rounding will give a correct result  at least as long as the local calendar used does not contain weird time jumps other than DST and leap seconds    Note that this still assumes that date1 and date2 are set to the same time of day  For different times of day  you d first have to define what  date difference  means  as pointed out by Jon Skeet

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Simple diff  without lib          Get a diff between two dates     param date1 the oldest date     param date2 the newest date     param timeUnit the unit in which you want the diff     return the diff value  in the provided unit     public static long getDateDiff Date date1  Date date2  TimeUnit timeUnit        long diffInMillies   date2 getTime   - date1 getTime        return timeUnit convert diffInMillies TimeUnit MILLISECONDS       And then can you call   getDateDiff date1 date2 TimeUnit MINUTES     to get the diff of the 2 dates in minutes unit   TimeUnit is java util concurrent TimeUnit  a standard Java enum going from nanos to days     Human readable diff  without lib   public static Map lt TimeUnit Long gt  computeDiff Date date1  Date date2         long diffInMillies   date2 getTime   - date1 getTime           create the list     List lt TimeUnit gt  units   new ArrayList lt TimeUnit gt  EnumSet allOf TimeUnit class        Collections reverse units          create the result map of TimeUnit and difference     Map lt TimeUnit Long gt  result   new LinkedHashMap lt TimeUnit Long gt         long milliesRest   diffInMillies       for   TimeUnit unit   units                calculate difference in millisecond          long diff   unit convert milliesRest TimeUnit MILLISECONDS           long diffInMilliesForUnit   unit toMillis diff           milliesRest   milliesRest - diffInMilliesForUnit             put the result in the map         result put unit diff              return result      http   ideone com 5dXeu6  The output is something like Map  DAYS 1  HOURS 3  MINUTES 46  SECONDS 40  MILLISECONDS 0  MICROSECONDS 0  NANOSECONDS 0   with the units ordered   You just have to convert that map to an user-friendly string     Warning  The above code snippets compute a simple diff between 2 instants  It can cause problems during a daylight saving switch  like explained in this post  This means if you compute the diff between dates with no time you may have a missing day hour   In my opinion the date diff is kind of subjective  especially on days  You may    count the number of 24h elapsed time  day 1 - day   1 day   24h count the number of elapsed time  taking care of daylight savings  day 1 - day   1   24h  but using midnight time and daylight savings it could be 0 day and 23h  count the number of day switches  which means day 1 1pm - day 11am   1 day  even if the elapsed time is just 2h  or 1h if there is a daylight saving  p    My answer is valid if your definition of date diff on days match the 1st case  With JodaTime  If you are using JodaTime you can get the diff for 2 instants  millies backed ReadableInstant  dates with   Interval interval   new Interval oldInstant  new Instant       But you can also get the diff for Local dates times      returns 4 because of the leap year of 366 days new Period LocalDate now    LocalDate now   plusDays 365 5   PeriodType years    getYears        this time it returns 5 new Period LocalDate now    LocalDate now   plusDays 365 5 1   PeriodType years    getYears        And you can also use these static methods Years yearsBetween LocalDate now    LocalDate now   plusDays 365 5   getYears

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public static String getDifferenceBtwTime Date dateTime         long timeDifferenceMilliseconds   new Date   getTime   - dateTime getTime        long diffSeconds   timeDifferenceMilliseconds   1000      long diffMinutes   timeDifferenceMilliseconds    60   1000       long diffHours   timeDifferenceMilliseconds    60   60   1000       long diffDays   timeDifferenceMilliseconds    60   60   1000   24       long diffWeeks   timeDifferenceMilliseconds    60   60   1000   24   7       long diffMonths    long   timeDifferenceMilliseconds    60   60   1000   24   30 41666666        long diffYears    long  timeDifferenceMilliseconds    1000   60   60   24   365         if  diffSeconds  lt  1            return  one sec ago         else if  diffMinutes  lt  1            return diffSeconds     seconds ago         else if  diffHours  lt  1            return diffMinutes     minutes ago         else if  diffDays  lt  1            return diffHours     hours ago         else if  diffWeeks  lt  1            return diffDays     days ago         else if  diffMonths  lt  1            return diffWeeks     weeks ago         else if  diffYears  lt  12            return diffMonths     months ago         else           return diffYears     years ago

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Here s a correct Java 7 solution in O 1  without any dependencies   public static int countDaysBetween Date date1  Date date2         Calendar c1   removeTime from date1        Calendar c2   removeTime from date2         if  c1 get YEAR     c2 get YEAR              return Math abs c1 get DAY OF YEAR  - c2 get DAY OF YEAR     1               ensure c1  lt   c2     if  c1 get YEAR   gt  c2 get YEAR             Calendar c   c1          c1   c2          c2   c            int y1   c1 get YEAR       int y2   c2 get YEAR       int d1   c1 get DAY OF YEAR       int d2   c2 get DAY OF YEAR        return d2     y2 - y1    365  - d1   countLeapYearsBetween y1  y2    1     private static int countLeapYearsBetween int y1  int y2         if  y1  lt  1    y2  lt  1            throw new IllegalArgumentException  Year must be  gt  0                  ensure y1  lt   y2     if  y1  gt  y2            int i   y1          y1   y2          y2   i             int diff   0       int firstDivisibleBy4   y1      if  firstDivisibleBy4   4    0            firstDivisibleBy4    4 -  y1   4             diff   y2 - firstDivisibleBy4 - 1      int divisibleBy4   diff  lt  0   0   diff   4   1       int firstDivisibleBy100   y1      if  firstDivisibleBy100   100    0            firstDivisibleBy100    100 -  firstDivisibleBy100   100             diff   y2 - firstDivisibleBy100 - 1      int divisibleBy100   diff  lt  0   0   diff   100   1       int firstDivisibleBy400   y1      if  firstDivisibleBy400   400    0            firstDivisibleBy400    400 -  y1   400             diff   y2 - firstDivisibleBy400 - 1      int divisibleBy400   diff  lt  0   0   diff   400   1       return divisibleBy4 - divisibleBy100   divisibleBy400      public static Calendar from Date date         Calendar c   Calendar getInstance        c setTime date        return c      public static Calendar removeTime Calendar c         c set HOUR OF DAY  0       c set MINUTE  0       c set SECOND  0       c set MILLISECOND  0        return c

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Since you are using Scala  there is a very good Scala library Lamma  With Lamma you can minus date directly with - operator  scala gt  Date 2015  5  5  - 2        minus days by int res1  io lamma Date   Date 2015 5 3   scala gt  Date 2015  5  15  - Date 2015  5  8       minus two days   gt  difference between two days res2  Int   7

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This is another sample  Which basically works for user-defined pattern      public static LinkedHashMap lt String  Object gt  checkDateDiff DateTimeFormatter dtfObj  String startDate  String endDate                 Map lt String  Object gt  dateDiffMap   new HashMap lt String  Object gt               DateTime start   DateTime parse startDate dtfObj             DateTime end   DateTime parse endDate dtfObj             Interval interval   new Interval start  end             Period period   interval toPeriod               dateDiffMap put  ISO-8601 PERIOD FORMAT   period             dateDiffMap put  YEAR   period getYears               dateDiffMap put  MONTH   period getMonths               dateDiffMap put  WEEK   period getWeeks               dateDiffMap put  DAY   period getWeeks                            dateDiffMap put  HOUR   period getHours               dateDiffMap put  MINUTE   period getMinutes               dateDiffMap put  SECOND   period getSeconds                return dateDiffMap

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Since the question is tagged with Scala   import scala concurrent duration   val diff    System currentTimeMillis   - oldDate getTime  milliseconds val diffSeconds   diff toSeconds val diffMinutes   diff toMinutes val diffHours   diff toHours val diffDays   diff toDays

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Following code can give you the desired output   String startDate    Jan 01 2015   DateTimeFormatter formatter   DateTimeFormatter ofPattern  MMM dd yyyy    LocalDate date   LocalDate parse startDate  formatter    String currentDate    Feb 11 2015   LocalDate date1   LocalDate parse currentDate  formatter    System out println date1 toEpochDay   - date toEpochDay

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After having read many answers and comments to this question  I was left with the impression that one either has to use the Joda time or else take into account some peculiarities with the daylight saving time etc  Since I didn t want to do either of these  I ended up writing a few lines of code to calculate the difference between two dates without using any date or time related Java classes   In the code below the numbers of year  month and day are the same as in real life  For example in December 24th 2015  the year   2015  the month   12 and the day   24   I want to share this code in case someone else wants to use it  There are 3 methods  1  A method to find out whether a given year is a leap year 2  A method to calculate the number of a given day in relation to January 1st of a given year 3  A method to calculate the number of days between any two dates using the method 2  number of the end date minus number of the start date    Here are the methods   1   public static boolean isLeapYear  int year          Every 4  year is a leap year  except if the year is divisible by 100 and not by 400       For example 1900 is not a leap year but 2000 is      boolean result   false       if  year   4    0            result   true            if  year   100    0            result   false            if  year   400    0            result   true             return result       2   public static int daysGoneSince  int yearZero  int year  int month  int day          Calculates the day number of the given date  day 1   January 1st in the yearZero        Validate the input     if  year  lt  yearZero    month  lt  1    month  gt  12    day  lt  1    day  gt  31              Throw an exception         throw new IllegalArgumentException  Too many or too few days in month or months in year or the year is smaller than year zero              else if  month    4    month    6    month    9    month    11     Months with 30 days         if  day    31                  Throw an exception             throw new IllegalArgumentException  Too many days in month                        else if  month    2     February 28 or 29         if  isLeapYear year                 if  day  gt  29                      Throw an exception                 throw new IllegalArgumentException  Too many days in month                                    else if  day  gt  28                  Throw an exception             throw new IllegalArgumentException  Too many days in month                           Start counting days     int days   0         Days in the target month until the target day     days   days   day         Days in the earlier months in the target year     for  int i   1  i  lt  month  i              switch  i                case 1  case 3  case 5              case 7  case 8  case 10              case 12                  days   days   31                  break              case 2                  days   days   28                  if  isLeapYear year                         days   days   1                                    break              case 4  case 6  case 9  case 11                  days   days   30                  break                         Days in the earlier years     for  int i   yearZero  i  lt  year  i              days   days   365          if  isLeapYear i                 days   days   1                       return days       3   public static int dateDiff  int startYear  int startMonth  int startDay  int endYear  int endMonth  int endDay         int yearZero         daysGoneSince presupposes that the first argument be smaller or equal to the second argument     if  10000   startYear   100   startMonth   startDay  gt  10000   endYear   100   endMonth   endDay     If the end date is earlier than the start date         yearZero   endYear            else           yearZero   startYear             return daysGoneSince yearZero  endYear  endMonth  endDay  - daysGoneSince yearZero  startYear  startMonth  startDay

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Let me show difference between Joda Interval and Days   DateTime start   new DateTime 2012  2  6  10  44  51  0   DateTime end   new DateTime 2012  2  6  11  39  47  1   Interval interval   new Interval start  end   Period period   interval toPeriod    System out println period getYears       years      period getMonths       months      period getWeeks       weeks      period getDays       days    System out println period getHours       hours      period getMinutes       minutes      period getSeconds       seconds       Result is    0 years  0 months   1 weeks  1 days    0 hours  54 minutes  56 seconds     Period can set PeriodType such as PeriodType yearMonthDay   PeriodType yearDayTime      Period p   new Period start  end  PeriodType yearMonthDayTime     System out println p getYears       years      p getMonths       months      p getWeeks       weeks      p getDays      days    System out println p getHours       hours      p getMinutes       minutes      p getSeconds       seconds       Result is    0 years  0 months   0 weeks  8 days    0 hours  54 minutes  56 seconds

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Earlier versions of Java you can try    public static String daysBetween Date createdDate  Date expiryDate             Calendar createdDateCal   Calendar getInstance            createdDateCal clear            createdDateCal setTime createdDate            Calendar expiryDateCal   Calendar getInstance            expiryDateCal clear            expiryDateCal setTime expiryDate             long daysBetween   0          while  createdDateCal before expiryDateCal                 createdDateCal add Calendar DAY OF MONTH  1               daysBetween                      return daysBetween

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If you need a formatted return String like  2 Days 03h 42m 07s   try this   public String fill2 int value        String ret   String valueOf value        if  ret length    lt  2          ret    0    ret                  return ret     public String get duration Date date1  Date date2                           TimeUnit timeUnit   TimeUnit SECONDS       long diffInMilli   date2 getTime   - date1 getTime        long s   timeUnit convert diffInMilli  TimeUnit MILLISECONDS        long days   s    24   60   60       long rest   s -  days   24   60   60       long hrs   rest    60   60       long rest1   rest -  hrs   60   60       long min   rest1   60            long sec   s   60       String dates           if  days  gt  0  dates   days     Days         dates    fill2  int  hrs     h        dates    fill2  int  min     m        dates    fill2  int  sec     s         return dates

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Just call getTime on each  take the difference  and divide by the number of milliseconds in a day

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There is an easy way to do this in java    create an utility method  public long getDaysBetweenDates Date d1  Date d2   return TimeUnit MILLISECONDS toDays d1 getTime   - d2 getTime         This method will return the number of days between the 2 dates  Either you can use the default java date format or can easily convert from any date format

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After wading through all the other answers  to keep the Java 7 Date type but be more precise standard with the Java 8 diff approach   public static long daysBetweenDates Date d1  Date d2        Instant instant1   d1 toInstant        Instant instant2   d2 toInstant        long diff   ChronoUnit DAYS between instant1  instant2       return diff

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public static void main String   args         String dateStart    01 14 2012 09 29 58       String dateStop    01 14 2012 10 31 48        SimpleDateFormat format   new SimpleDateFormat  MM dd yyyy HH mm ss         Date d1   null      Date d2   null       try           d1   format parse dateStart           d2   format parse dateStop            DateTime date11   new DateTime d1           DateTime date22   new DateTime d2           int days   Days daysBetween date11 withTimeAtStartOfDay    date22 withTimeAtStartOfDay    getDays            int hours   Hours hoursBetween date11  date22  getHours     24          int minutes   Minutes minutesBetween date11  date22  getMinutes     60          int seconds   Seconds secondsBetween date11  date22  getSeconds     60          if  hours  gt  0    minutes  gt  0    seconds  gt  0                days   days   1                     System out println days          catch  Exception e            e printStackTrace               This will give date diff for the same day as well

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Check example here http   www roseindia net java beginners DateDifferent shtml This example give you difference in days  hours  minutes  secs and milli sec s      import java util Calendar  import java util Date   public class DateDifferent       public static void main String   args            Date date1   new Date 2009  01  10           Date date2   new Date 2009  07  01           Calendar calendar1   Calendar getInstance            Calendar calendar2   Calendar getInstance            calendar1 setTime date1           calendar2 setTime date2           long milliseconds1   calendar1 getTimeInMillis            long milliseconds2   calendar2 getTimeInMillis            long diff   milliseconds2 - milliseconds1          long diffSeconds   diff   1000          long diffMinutes   diff    60   1000           long diffHours   diff    60   60   1000           long diffDays   diff    24   60   60   1000           System out println   nThe Date Different Example            System out println  Time in milliseconds      diff     milliseconds             System out println  Time in seconds      diffSeconds     seconds             System out println  Time in minutes      diffMinutes     minutes             System out println  Time in hours      diffHours     hours             System out println  Time in days      diffDays     days

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Not using the standard API  no  You can roll your own doing something like this   class Duration       private final TimeUnit unit      private final long length                 Or you can use Joda   DateTime a        b        Duration d   new Duration a  b

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int diffInDays    int    newerDate getTime   - olderDate getTime                         1000   60   60   24      Note that this works with UTC dates  so the difference may be a day off if you look at local dates  And getting it to work correctly with local dates requires a completely different approach due to daylight savings time

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Note  startDate and endDates are -  java util Date   import org joda time Duration  import org joda time Interval     Use  getTime   unless it is a joda DateTime object Interval interval   new Interval startDate getTime    endDate getTime     Duration period   interval toDuration      gives the number of days elapsed between start  period getStandardDays      and end date  Similar to days  you can also  get hours  minutes and seconds  period getStandardHours    period getStandardMinutes    period getStandardSeconds

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Best thing to do is   Date1-Date2  86 400 000    That number is the number of milliseconds in a day    One date-other date gives you difference in milliseconds    Collect the answer in a double variable

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If you want to fix the issue for date ranges that cross daylight savings time boundary  e g  one date in summer time and the other one in winter time   you can use this to get the difference in days   public static long calculateDifferenceInDays Date start  Date end  Locale locale        Calendar cal   Calendar getInstance locale        cal setTime start       cal set Calendar HOUR OF DAY  0       cal set Calendar MINUTE  0       cal set Calendar SECOND  0       cal set Calendar MILLISECOND  0       long startTime   cal getTimeInMillis         cal setTime end       cal set Calendar HOUR OF DAY  0       cal set Calendar MINUTE  0       cal set Calendar SECOND  0       cal set Calendar MILLISECOND  0       long endTime   cal getTimeInMillis            calculate the offset if one of the dates is in summer time and the other one in winter time     TimeZone timezone   cal getTimeZone        int offsetStart   timezone getOffset startTime       int offsetEnd   timezone getOffset endTime       int offset   offsetEnd - offsetStart       return TimeUnit MILLISECONDS toDays endTime - startTime   offset

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Just use below method with two Date objects  If you want to pass current date  just pass new Date   as a second parameter as it is initialised with current time   public String getDateDiffString Date dateOne  Date dateTwo        long timeOne   dateOne getTime        long timeTwo   dateTwo getTime        long oneDay   1000   60   60   24      long delta    timeTwo - timeOne    oneDay       if  delta  gt  0            return  dateTwo is     delta     days after dateOne             else           delta    -1          return  dateTwo is     delta     days before dateOne              Also  apart from from number of days  if  you want other parameter difference too  use below snippet   int year   delta   365  int rest   delta   365  int month   rest   30  rest   rest   30  int weeks   rest   7  int days   rest   7    P S Code is entirely taken from an SO answer

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If you have d1 and d2 as your dates  the best solution is probably the following   int days1   d1 getTime    60 60 24 1000    find the number of days since the epoch  int days2   d2 getTime    60 60 24 1000     then just say  days2-days1   or whatever

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Take a look at Joda Time  which is an improved Date Time API for Java and should work fine with Scala

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A slightly simpler alternative    System currentTimeMillis   - oldDate getTime     As for  nicer   well  what exactly do you need  The problem with representing time durations as a number of hours and days etc  is that it may lead to inaccuracies and wrong expectations due to the complexity of dates  e g  days can have 23 or 25 hours due to daylight savings time

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That s probably the most straightforward way to do it - perhaps it s because I ve been coding in Java  with its admittedly clunky date and time libraries  for a while now  but that code looks  simple and nice  to me   Are you happy with the result being returned in milliseconds  or is part of your question that you would prefer to have it returned in some alternative format

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I liked the TimeUnit-based approach until I found out that it only covers the trivial cases where the number of how many units of one timeunit are in the next higher unit is fixed  This breaks apart when you want to know how many months  year  etc are in between    here is a counting approach  not as efficient as some others  but it seems to work for me and takes into account DST  too   public static String getOffsetAsString  Calendar cNow  Calendar cThen        Calendar cBefore      Calendar cAfter      if   cNow getTimeInMillis    lt  cThen getTimeInMillis              cBefore     Calendar  cNow clone            cAfter   cThen        else           cBefore     Calendar  cThen clone            cAfter   cNow               compute diff     Map lt Integer  Long gt  diffMap   new HashMap lt Integer  Long gt         int   calFields     Calendar YEAR  Calendar MONTH  Calendar DAY OF MONTH  Calendar HOUR OF DAY  Calendar MINUTE  Calendar SECOND  Calendar MILLISECOND       for   int i   0  i  lt  calFields length  i              int field   calFields  i           long    d   computeDist  cAfter  cBefore  field           diffMap put  field  d             final String result   String format    dY  02dM  dT  02d  02d  02d  03d               diffMap get  Calendar YEAR   diffMap get  Calendar MONTH   diffMap get  Calendar DAY OF MONTH   diffMap get  Calendar HOUR OF DAY   diffMap get  Calendar MINUTE   diffMap get  Calendar SECOND   diffMap get  Calendar MILLISECOND        return result     private static int computeDist  Calendar cAfter  Calendar cBefore  int field        cBefore setLenient  true       System out print   D     new Date  cBefore getTimeInMillis        ---     new Date  cAfter getTimeInMillis                 int count   0      if   cAfter getTimeInMillis    gt  cBefore getTimeInMillis              int fVal   cBefore get  field           while   cAfter getTimeInMillis    gt   cBefore getTimeInMillis                  count                fVal   cBefore get  field               cBefore set  field  fVal   1               System out print  count            fVal   1           new Date  cBefore getTimeInMillis                                int result   count - 1          cBefore set  field  fVal           System out println       result     at      field     cb       new Date  cBefore getTimeInMillis              return result            return 0

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Subtracting the dates in milliseconds works  as described in another post   but you have to use HOUR OF DAY and not HOUR when clearing the time parts of your dates   public static final long MSPERDAY   60   60   24   1000      final Calendar dateStartCal   Calendar getInstance    dateStartCal setTime dateStart   dateStartCal set Calendar HOUR OF DAY  0      Crucial  dateStartCal set Calendar MINUTE  0   dateStartCal set Calendar SECOND  0   dateStartCal set Calendar MILLISECOND  0   final Calendar dateEndCal   Calendar getInstance    dateEndCal setTime dateEnd   dateEndCal set Calendar HOUR OF DAY  0      Crucial  dateEndCal set Calendar MINUTE  0   dateEndCal set Calendar SECOND  0   dateEndCal set Calendar MILLISECOND  0   final long dateDifferenceInDays     dateStartCal getTimeInMillis                                     - dateEndCal getTimeInMillis                                         MSPERDAY  if  dateDifferenceInDays  gt  15           Do something if difference  gt  15 days

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Since all the answers here are correct but use legacy java or 3rd party libs like joda or similar  I will just drop another way using new java time classes in Java 8 and later  See Oracle Tutorial   Use LocalDate and ChronoUnit   LocalDate d1   LocalDate of 2017  5  1   LocalDate d2   LocalDate of 2017  5  18    long days   ChronoUnit DAYS between d1  d2   System out println  days

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tl dr  Convert your obsolete java util Date objects to their replacement  java time Instant  Then calculate the elapsed time as a Duration   Duration d        Duration between                       Calculate the span of time between two moments as a number of hours  minutes  and seconds          myJavaUtilDate toInstant           Convert legacy class to modern class by calling new method added to the old class          Instant now                        Capture the current moment in UTC  About two and a half hours later in this example               d toString    PT2H34M56S      d toMinutes    154      d toMinutesPart    34   ISO 8601 Format  PnYnMnDTnHnMnS  The sensible standard ISO 8601 defines a concise textual representation of a span of time as a number of years  months  days  hours  etc  The standard calls such such a span a duration  The format is PnYnMnDTnHnMnS where the P means  Period   the T separates the date portion from the time portion  and in between are numbers followed by a letter   Examples    P3Y6M4DT12H30M5Sthree years  six months  four days  twelve hours  thirty minutes  and five seconds PT4H30MFour and a half hours   java time  The java time framework built into Java 8 and later supplants the troublesome old java util Date java util Calendar classes  The new classes are inspired by the highly successful Joda-Time framework  intended as its successor  similar in concept but re-architected  Defined by JSR 310  Extended by the ThreeTen-Extra project  See the Tutorial   Moment  The Instant class represents a moment on the timeline in UTC with a resolution of nanoseconds  up to nine  9  digits of a decimal fraction     Instant instant   Instant now         Capture current moment in UTC    Best to avoid the legacy classes such as Date Calendar  But if you must inter-operate with old code not yet updated to java time  convert back and forth  Call new conversion methods added to the old classes  For moving from a java util Date to an Instant  call Date  toInstant    Instant instant   myJavaUtilDate toInstant         Convert from legacy  java util Date  class to modern  java time Instant  class    Span of time  The java time classes have split this idea of representing a span of time as a number of years  months  days  hours  minutes  seconds into two halves    Period for years  months  days Duration for days  hours  minutes  seconds   Here is an example   ZoneId zoneId   ZoneId of    America Montreal     ZonedDateTime now   ZonedDateTime now   zoneId    ZonedDateTime future   now plusMinutes   63    Duration duration   Duration between   now   future      Dump to console   Both Period and Duration use the ISO 8601 standard for generating a String representation of their value   System out println    now      now     to future      now           duration         now  2015-11-26T00 46 48 016-05 00 America Montreal  to future  2015-11-26T00 46 48 016-05 00 America Montreal    PT1H3M   Java 9 adds methods to Duration to get the days part  hours part  minutes part  and seconds part   You can get the total number of days or hours or minutes or seconds or milliseconds or nanoseconds in the entire Duration   long totalHours   duration toHours      In Java 9 the Duration class gets new methods for returning the various parts of days  hours  minutes  seconds  milliseconds nanoseconds  Call the to   Part methods  toDaysPart    toHoursPart    and so on   ChronoUnit  If you only care about a simpler larger granularity of time  such as    number of days elapsed     use the ChronoUnit enum   long daysElapsed   ChronoUnit DAYS between  earlier   later      Another example   Instant now   Instant now    Instant later   now plus  Duration ofHours  2          long minutesElapsed   ChronoUnit MINUTES between  now   later         120     About java time  The java time framework is built into Java 8 and later  These classes supplant the troublesome old legacy date-time classes such as java util Date  Calendar   amp  SimpleDateFormat   The Joda-Time project  now in maintenance mode  advises migration to java time   To learn more  see the Oracle Tutorial  And search Stack Overflow for many examples and explanations  Specification is JSR 310   Where to obtain the java time classes     Java SE 8 and SE 9 and later   Built-in   Part of the standard Java API with a bundled implementation  Java 9 adds some minor features and fixes   Java SE 6 and SE 7   Much of the java time functionality is back-ported to Java 6  amp  7 in ThreeTen-Backport   Android   The ThreeTenABP project adapts ThreeTen-Backport  mentioned above  for Android specifically  See How to use        The ThreeTen-Extra project extends java time with additional classes  This project is a proving ground for possible future additions to java time  You may find some useful classes here such as Interval  YearWeek  YearQuarter  and more     Joda-Time  UPDATE  The Joda-Time project is now in maintenance mode  with the team advising migration to the java time classes  I leave this section intact for history   The Joda-Time library uses ISO 8601 for its defaults  Its Period class parses and generates these PnYnMnDTnHnMnS strings   DateTime now   DateTime now       Caveat  Ignoring the important issue of time zones  Period period   new Period  now  now plusHours  4   plusMinutes  30    System out println   period      period      Renders   period  PT4H30M

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The JDK Date API is horribly broken unfortunately   I recommend using Joda Time library   Joda Time has a concept of time Interval   Interval interval   new Interval oldTime  new Instant       EDIT  By the way  Joda has two concepts  Interval for representing an interval of time between two time instants  represent time between 8am and 10am   and a Duration that represents a length of time without the actual time boundaries  e g  represent two hours    If you only care about time comparisions  most Date implementations  including the JDK one  implements Comparable interface which allows you to use the Comparable compareTo

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You need to define your problem more clearly  You could just take the number of milliseconds between the two Date objects and divide by the number of milliseconds in 24 hours  for example    but    This won t take time zones into consideration - Date is always in UTC This won t take daylight saving time into consideration  where there can be days which are only 23 hours long  for example  Even within UTC  how many days are there in August 16th 11pm to August 18th 2am  It s only 27 hours  so does that mean one day  Or should it be three days because it covers three dates

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The following is one solution  as there are numerous ways we can achieve this     import java util        int syear   2000     int eyear   2000     int smonth   2   Feb    int emonth   3   Mar    int sday   27     int eday   1     Date startDate   new Date syear-1900 smonth-1 sday      Date endDate   new Date eyear-1900 emonth-1 eday      int difInDays    int    endDate getTime   - startDate getTime     1000 60 60 24

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Use GMT time zone to get an instance of the Calendar  set the time using the set method of Calendar class  The GMT timezone has 0 offset  not really important  and daylight saving time flag set to false       final Calendar cal   Calendar getInstance TimeZone getTimeZone  GMT          cal set Calendar YEAR  2011       cal set Calendar MONTH  9       cal set Calendar DAY OF MONTH  29       cal set Calendar HOUR  0       cal set Calendar MINUTE  0       cal set Calendar SECOND  0       final Date startDate   cal getTime         cal set Calendar YEAR  2011       cal set Calendar MONTH  12       cal set Calendar DAY OF MONTH  21       cal set Calendar HOUR  0       cal set Calendar MINUTE  0       cal set Calendar SECOND  0       final Date endDate   cal getTime         System out println  endDate getTime   - startDate getTime       1000l   60l   60l   24l

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Using the java time framework built into Java 8   ZonedDateTime now   ZonedDateTime now    ZonedDateTime oldDate   now minusDays 1  minusMinutes 10   Duration duration   Duration between oldDate  now   System out println  quot ISO-8601   quot    duration   System out println  quot Minutes   quot    duration toMinutes      Output   ISO-8601  PT24H10M Minutes  1450  For more info  see the Oracle Tutorial and the ISO 8601 standard

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int daysDiff    date1 getTime   - date2 getTime      MILLIS PER DAY

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Just to answer the initial question   Put the following code in a Function like Long getAge      Date dahora   new Date    long MillisToYearsByDiv   1000l  60l   60l   24l   365l  long javaOffsetInMillis   1990l   MillisToYearsByDiv  long realNowInMillis   dahora getTime     javaOffsetInMillis  long realBirthDayInMillis   this getFechaNac   getTime     javaOffsetInMillis  long ageInMillis   realNowInMillis - realBirthDayInMillis   return ageInMillis   MillisToYearsByDiv    The most important here is to work with long numbers when multiplying and dividing  And of course  the offset that Java applies in its calculus of Dates

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There are many ways you can find the difference between dates  amp  times   One of the simplest ways that I know of would be         Calendar calendar1   Calendar getInstance          Calendar calendar2   Calendar getInstance          calendar1 set 2012  04  02         calendar2 set 2012  04  04         long milsecs1  calendar1 getTimeInMillis          long milsecs2   calendar2 getTimeInMillis          long diff   milsecs2 - milsecs1        long dsecs   diff   1000        long dminutes   diff    60   1000         long dhours   diff    60   60   1000         long ddays   diff    24   60   60   1000          System out println  Your Day Difference   ddays     The print statement is just an example - you can format it  the way you like

[java] Calculating the difference between two Java date instances

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