Why is January month 0 in Java Calendar

Question

In java util Calendar  January is defined as month 0  not month 1  Is there any specific reason to that    I have seen many people getting confused about that

User · Answer

C based languages copy C to some degree  The tm structure  defined in time h  has an integer field tm mon with the  commented  range of 0-11   C based languages start arrays at index 0  So this was convenient for outputting a string in an array of month names  with tm mon as the index

User · Answer

It s just part of the horrendous mess which is the Java date time API  Listing what s wrong with it would take a very long time  and I m sure I don t know half of the problems   Admittedly working with dates and times is tricky  but aaargh anyway   Do yourself a favour and use Joda Time instead  or possibly JSR-310   EDIT  As for the reasons why - as noted in other answers  it could well be due to old C APIs  or just a general feeling of starting everything from 0    except that days start with 1  of course  I doubt whether anyone outside the original implementation team could really state reasons - but again  I d urge readers not to worry so much about why bad decisions were taken  as to look at the whole gamut of nastiness in java util Calendar and find something better   One point which is in favour of using 0-based indexes is that it makes things like  arrays of names  easier      I  know  there are 12 months String   monthNames   new String 12      and populate    String name   monthNames calendar get Calendar MONTH      Of course  this fails as soon as you get a calendar with 13 months    but at least the size specified is the number of months you expect   This isn t a good reason  but it s a reason     EDIT  As a comment sort of requests some ideas about what I think is wrong with Date Calendar    Surprising bases  1900 as the year base in Date  admittedly for deprecated constructors  0 as the month base in both  Mutability - using immutable types makes it much simpler to work with what are really effectively values An insufficient set of types  it s nice to have Date and Calendar as different things   but the separation of  local  vs  zoned  values is missing  as is date time vs date vs time An API which leads to ugly code with magic constants  instead of clearly named methods An API which is very hard to reason about - all the business about when things are recomputed etc The use of parameterless constructors to default to  now   which leads to hard-to-test code The Date toString   implementation which always uses the system local time zone  that s confused many Stack Overflow users before now

User · Answer

Because programmers are obsessed with 0-based indexes  OK  it s a bit more complicated than that  it makes more sense when you re working with lower-level logic to use 0-based indexing  But by and large  I ll still stick with my first sentence

User · Answer

In Java 8  there is a new Date Time API JSR 310 that is more sane  The spec lead is the same as the primary author of JodaTime and they share many similar concepts and patterns

User · Answer

In Java 8  there is a new Date Time API JSR 310 that is more sane  The spec lead is the same as the primary author of JodaTime and they share many similar concepts and patterns

User · Answer

There has been a lot of answers to this  but I will give my view on the subject anyway  The reason behind this odd behavior  as stated previously  comes from the POSIX C time h where the months were stored in an int with the range 0-11  To explain why  look at it like this  years and days are considered numbers in spoken language  but months have their own names  So because January is the first month it will be stored as offset 0  the first array element  monthname JANUARY  would be  quot January quot   The first month in the year is the first month array element  The day numbers on the other hand  since they do not have names  storing them in an int as 0-30 would be confusing  add a lot of day 1 instructions for outputting and  of course  be prone to alot of bugs  That being said  the inconsistency is confusing  especially in javascript  which also has inherited this  quot feature quot    a scripting language where this should be abstracted far away from the langague  TL DR  Because months have names and days of the month do not

User · Answer

Because everything starts with 0  This is a basic fact of programming in Java  If one thing were to deviate from that  then that would lead to a whole slue of confusion  Let s not argue the formation of them and code with them

User · Answer

It s just part of the horrendous mess which is the Java date time API  Listing what s wrong with it would take a very long time  and I m sure I don t know half of the problems   Admittedly working with dates and times is tricky  but aaargh anyway   Do yourself a favour and use Joda Time instead  or possibly JSR-310   EDIT  As for the reasons why - as noted in other answers  it could well be due to old C APIs  or just a general feeling of starting everything from 0    except that days start with 1  of course  I doubt whether anyone outside the original implementation team could really state reasons - but again  I d urge readers not to worry so much about why bad decisions were taken  as to look at the whole gamut of nastiness in java util Calendar and find something better   One point which is in favour of using 0-based indexes is that it makes things like  arrays of names  easier      I  know  there are 12 months String   monthNames   new String 12      and populate    String name   monthNames calendar get Calendar MONTH      Of course  this fails as soon as you get a calendar with 13 months    but at least the size specified is the number of months you expect   This isn t a good reason  but it s a reason     EDIT  As a comment sort of requests some ideas about what I think is wrong with Date Calendar    Surprising bases  1900 as the year base in Date  admittedly for deprecated constructors  0 as the month base in both  Mutability - using immutable types makes it much simpler to work with what are really effectively values An insufficient set of types  it s nice to have Date and Calendar as different things   but the separation of  local  vs  zoned  values is missing  as is date time vs date vs time An API which leads to ugly code with magic constants  instead of clearly named methods An API which is very hard to reason about - all the business about when things are recomputed etc The use of parameterless constructors to default to  now   which leads to hard-to-test code The Date toString   implementation which always uses the system local time zone  that s confused many Stack Overflow users before now

User · Answer

C based languages copy C to some degree  The tm structure  defined in time h  has an integer field tm mon with the  commented  range of 0-11   C based languages start arrays at index 0  So this was convenient for outputting a string in an array of month names  with tm mon as the index

User · Answer

In addition to DannySmurf s answer of laziness  I ll add that it s to encourage you to use the constants  such as Calendar JANUARY

User · Answer

It isn t exactly defined as zero per se  it s defined as Calendar January  It is the problem of using ints as constants instead of enums  Calendar January    0

User · Answer

I d say laziness  Arrays start at 0  everyone knows that   the months of the year are an array  which leads me to believe that some engineer at Sun just didn t bother to put this one little nicety into the Java code

User · Answer

It isn t exactly defined as zero per se  it s defined as Calendar January  It is the problem of using ints as constants instead of enums  Calendar January    0

User · Answer

java time Month Java provides you another way to use 1 based indexes for months  Use the java time Month enum  One object is predefined for each of the twelve months  They have numbers assigned to each 1-12 for January-December  call getValue for the number  Make use of Month JULY  Gives you 7  instead of Calendar JULY  Gives you 6    import java time

User · Answer

Because programmers are obsessed with 0-based indexes  OK  it s a bit more complicated than that  it makes more sense when you re working with lower-level logic to use 0-based indexing  But by and large  I ll still stick with my first sentence

User · Answer

In Java 8  there is a new Date Time API JSR 310 that is more sane  The spec lead is the same as the primary author of JodaTime and they share many similar concepts and patterns

User · Answer

Because doing math with months is much easier   1 month after December is January  but to figure this out normally you would have to take the month number and do math  12   1   13    What month is 13    I know  I can fix this quickly by using a modulus of 12    12   1    12   1   This works just fine for 11 months until November      11   1    12   0    What month is 0    You can make all of this work again by subtracting 1 before you add the month  then do your modulus and finally add 1 back again    aka work around an underlying problem     11 - 1   1    12    1   12    Lots of magical numbers    Now let s think about the problem with months 0 - 11    0   1    12   1    February  1   1    12   2    March  2   1    12   3    April  3   1    12   4    May  4   1    12   5    June  5   1    12   6    July  6   1    12   7    August  7   1    12   8    September  8   1    12   9    October  9   1    12   10    November  10   1    12   11    December  11   1    12   0    January   All of the months work the same and a work around isn t necessary

User · Answer

Probably because C s  struct tm  does the same

User · Answer

In Java 8  there is a new Date Time API JSR 310 that is more sane  The spec lead is the same as the primary author of JodaTime and they share many similar concepts and patterns

User · Answer

It s just part of the horrendous mess which is the Java date time API  Listing what s wrong with it would take a very long time  and I m sure I don t know half of the problems   Admittedly working with dates and times is tricky  but aaargh anyway   Do yourself a favour and use Joda Time instead  or possibly JSR-310   EDIT  As for the reasons why - as noted in other answers  it could well be due to old C APIs  or just a general feeling of starting everything from 0    except that days start with 1  of course  I doubt whether anyone outside the original implementation team could really state reasons - but again  I d urge readers not to worry so much about why bad decisions were taken  as to look at the whole gamut of nastiness in java util Calendar and find something better   One point which is in favour of using 0-based indexes is that it makes things like  arrays of names  easier      I  know  there are 12 months String   monthNames   new String 12      and populate    String name   monthNames calendar get Calendar MONTH      Of course  this fails as soon as you get a calendar with 13 months    but at least the size specified is the number of months you expect   This isn t a good reason  but it s a reason     EDIT  As a comment sort of requests some ideas about what I think is wrong with Date Calendar    Surprising bases  1900 as the year base in Date  admittedly for deprecated constructors  0 as the month base in both  Mutability - using immutable types makes it much simpler to work with what are really effectively values An insufficient set of types  it s nice to have Date and Calendar as different things   but the separation of  local  vs  zoned  values is missing  as is date time vs date vs time An API which leads to ugly code with magic constants  instead of clearly named methods An API which is very hard to reason about - all the business about when things are recomputed etc The use of parameterless constructors to default to  now   which leads to hard-to-test code The Date toString   implementation which always uses the system local time zone  that s confused many Stack Overflow users before now

User · Answer

In addition to DannySmurf s answer of laziness  I ll add that it s to encourage you to use the constants  such as Calendar JANUARY

User · Answer

Probably because C s  struct tm  does the same

User · Answer

For me  nobody explains it better than mindpro com       Gotchas      java util GregorianCalendar has far fewer bugs and gotchas than the   old java util Date class but it is still no picnic       Had there been programmers when Daylight Saving Time was first   proposed  they would have vetoed it as insane and intractable  With   daylight saving  there is a fundamental ambiguity  In the fall when   you set your clocks back one hour at 2 AM there are two different   instants in time both called 1 30 AM local time  You can tell them   apart only if you record whether you intended daylight saving or   standard time with the reading        Unfortunately  there is no way to tell GregorianCalendar which you   intended  You must resort to telling it the local time with the dummy   UTC TimeZone to avoid the ambiguity  Programmers usually close their   eyes to this problem and just hope nobody does anything during this   hour       Millennium bug  The bugs are still not out of the Calendar classes    Even in JDK  Java Development Kit  1 3 there is a 2001 bug  Consider   the following code   GregorianCalendar gc   new GregorianCalendar    gc setLenient  false       Bug only manifests if lenient set false    gc set  2001  1  1  1  0  0    int year   gc get   Calendar YEAR       throws exception          The bug disappears at 7AM on 2001 01 01 for MST       GregorianCalendar is controlled by a giant of pile of untyped int   magic constants  This technique totally destroys any hope of   compile-time error checking  For example to get the month you use   GregorianCalendar  get Calendar MONTH         GregorianCalendar has the raw   GregorianCalendar get Calendar ZONE OFFSET  and the daylight savings   GregorianCalendar  get  Calendar  DST OFFSET   but no way to get the   actual time zone offset being used  You must get these two separately   and add them together       GregorianCalendar set  year  month  day  hour  minute  does not set   the seconds to 0       DateFormat and GregorianCalendar do not mesh properly  You must   specify the Calendar twice  once indirectly as a Date       If the user has not configured his time zone correctly it will default   quietly to either PST or GMT       In GregorianCalendar  Months are numbered starting at January 0    rather than 1 as everyone else on the planet does  Yet days start at 1   as do days of the week with Sunday 1  Monday 2     Saturday 7  Yet   DateFormat  parse behaves in the traditional way with January 1

User · Answer

Because programmers are obsessed with 0-based indexes  OK  it s a bit more complicated than that  it makes more sense when you re working with lower-level logic to use 0-based indexing  But by and large  I ll still stick with my first sentence

User · Answer

I d say laziness  Arrays start at 0  everyone knows that   the months of the year are an array  which leads me to believe that some engineer at Sun just didn t bother to put this one little nicety into the Java code

User · Answer

Personally  I took the strangeness of the Java calendar API as an indication that I needed to divorce myself from the Gregorian-centric mindset and try to program more agnostically in that respect   Specifically  I learned once again to avoid hardcoded constants for things like months   Which of the following is more likely to be correct   if  date getMonth      3  out print  March     if  date getMonth      Calendar MARCH  out print  March      This illustrates one thing that irks me a little about Joda Time - it may encourage programmers to think in terms of hardcoded constants    Only a little  though   It s not as if Joda is forcing programmers to program badly

User · Answer

It isn t exactly defined as zero per se  it s defined as Calendar January  It is the problem of using ints as constants instead of enums  Calendar January    0

User · Answer

Because language writing is harder than it looks  and handling time in particular is a lot harder than most people think  For a small part of the problem  in reality  not Java   see the YouTube video  The Problem with Time  amp  Timezones - Computerphile  at https   www youtube com watch v -5wpm-gesOY  Don t be surprised if your head falls off from laughing in confusion

User · Answer

It s just part of the horrendous mess which is the Java date time API  Listing what s wrong with it would take a very long time  and I m sure I don t know half of the problems   Admittedly working with dates and times is tricky  but aaargh anyway   Do yourself a favour and use Joda Time instead  or possibly JSR-310   EDIT  As for the reasons why - as noted in other answers  it could well be due to old C APIs  or just a general feeling of starting everything from 0    except that days start with 1  of course  I doubt whether anyone outside the original implementation team could really state reasons - but again  I d urge readers not to worry so much about why bad decisions were taken  as to look at the whole gamut of nastiness in java util Calendar and find something better   One point which is in favour of using 0-based indexes is that it makes things like  arrays of names  easier      I  know  there are 12 months String   monthNames   new String 12      and populate    String name   monthNames calendar get Calendar MONTH      Of course  this fails as soon as you get a calendar with 13 months    but at least the size specified is the number of months you expect   This isn t a good reason  but it s a reason     EDIT  As a comment sort of requests some ideas about what I think is wrong with Date Calendar    Surprising bases  1900 as the year base in Date  admittedly for deprecated constructors  0 as the month base in both  Mutability - using immutable types makes it much simpler to work with what are really effectively values An insufficient set of types  it s nice to have Date and Calendar as different things   but the separation of  local  vs  zoned  values is missing  as is date time vs date vs time An API which leads to ugly code with magic constants  instead of clearly named methods An API which is very hard to reason about - all the business about when things are recomputed etc The use of parameterless constructors to default to  now   which leads to hard-to-test code The Date toString   implementation which always uses the system local time zone  that s confused many Stack Overflow users before now

User · Answer

There has been a lot of answers to this  but I will give my view on the subject anyway  The reason behind this odd behavior  as stated previously  comes from the POSIX C time h where the months were stored in an int with the range 0-11  To explain why  look at it like this  years and days are considered numbers in spoken language  but months have their own names  So because January is the first month it will be stored as offset 0  the first array element  monthname JANUARY  would be  quot January quot   The first month in the year is the first month array element  The day numbers on the other hand  since they do not have names  storing them in an int as 0-30 would be confusing  add a lot of day 1 instructions for outputting and  of course  be prone to alot of bugs  That being said  the inconsistency is confusing  especially in javascript  which also has inherited this  quot feature quot    a scripting language where this should be abstracted far away from the langague  TL DR  Because months have names and days of the month do not

User · Answer

Because everything starts with 0  This is a basic fact of programming in Java  If one thing were to deviate from that  then that would lead to a whole slue of confusion  Let s not argue the formation of them and code with them

User · Answer

In addition to DannySmurf s answer of laziness  I ll add that it s to encourage you to use the constants  such as Calendar JANUARY

User · Answer

java time Month Java provides you another way to use 1 based indexes for months  Use the java time Month enum  One object is predefined for each of the twelve months  They have numbers assigned to each 1-12 for January-December  call getValue for the number  Make use of Month JULY  Gives you 7  instead of Calendar JULY  Gives you 6    import java time

User · Answer

Because programmers are obsessed with 0-based indexes  OK  it s a bit more complicated than that  it makes more sense when you re working with lower-level logic to use 0-based indexing  But by and large  I ll still stick with my first sentence

User · Answer

C based languages copy C to some degree  The tm structure  defined in time h  has an integer field tm mon with the  commented  range of 0-11   C based languages start arrays at index 0  So this was convenient for outputting a string in an array of month names  with tm mon as the index

User · Answer

Personally  I took the strangeness of the Java calendar API as an indication that I needed to divorce myself from the Gregorian-centric mindset and try to program more agnostically in that respect   Specifically  I learned once again to avoid hardcoded constants for things like months   Which of the following is more likely to be correct   if  date getMonth      3  out print  March     if  date getMonth      Calendar MARCH  out print  March      This illustrates one thing that irks me a little about Joda Time - it may encourage programmers to think in terms of hardcoded constants    Only a little  though   It s not as if Joda is forcing programmers to program badly

User · Answer

tl dr  Month FEBRUARY getValue       February   2       2   Details  The Answer by Jon Skeet is correct   Now we have a modern replacement for those troublesome old legacy date-time classes  the java time classes   java time Month  Among those classes is the Month enum  An enum carries one or more predefined objects  objects that are automatically instantiated when the class loads  On Month we have a dozen such objects  each given a name  JANUARY  FEBRUARY  MARCH  and so on  Each of those is a static final public class constant  You can use and pass these objects anywhere in your code  Example  someMethod  Month AUGUST    Fortunately  they have sane numbering  1-12 where 1 is January and 12 is December   Get a Month object for a particular month number  1-12    Month month   Month of  2        2   February    Going the other direction  ask a Month object for its month number   int monthNumber   Month FEBRUARY getValue        February   2    Many other handy methods on this class  such as knowing the number of days in each month  The class can even generate a localized name of the month   You can get the localized name of the month  in various lengths or abbreviations   String output        Month FEBRUARY getDisplayName           TextStyle FULL            Locale CANADA FRENCH              f  vrier   Also  you should pass objects of this enum around your code base rather than mere integer numbers  Doing so provides type-safety  ensures a valid range of values  and makes your code more self-documenting  See Oracle Tutorial if unfamiliar with the surprisingly powerful enum facility in Java   You also may find useful the Year and YearMonth classes     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  java text 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

User · Answer

For me  nobody explains it better than mindpro com       Gotchas      java util GregorianCalendar has far fewer bugs and gotchas than the   old java util Date class but it is still no picnic       Had there been programmers when Daylight Saving Time was first   proposed  they would have vetoed it as insane and intractable  With   daylight saving  there is a fundamental ambiguity  In the fall when   you set your clocks back one hour at 2 AM there are two different   instants in time both called 1 30 AM local time  You can tell them   apart only if you record whether you intended daylight saving or   standard time with the reading        Unfortunately  there is no way to tell GregorianCalendar which you   intended  You must resort to telling it the local time with the dummy   UTC TimeZone to avoid the ambiguity  Programmers usually close their   eyes to this problem and just hope nobody does anything during this   hour       Millennium bug  The bugs are still not out of the Calendar classes    Even in JDK  Java Development Kit  1 3 there is a 2001 bug  Consider   the following code   GregorianCalendar gc   new GregorianCalendar    gc setLenient  false       Bug only manifests if lenient set false    gc set  2001  1  1  1  0  0    int year   gc get   Calendar YEAR       throws exception          The bug disappears at 7AM on 2001 01 01 for MST       GregorianCalendar is controlled by a giant of pile of untyped int   magic constants  This technique totally destroys any hope of   compile-time error checking  For example to get the month you use   GregorianCalendar  get Calendar MONTH         GregorianCalendar has the raw   GregorianCalendar get Calendar ZONE OFFSET  and the daylight savings   GregorianCalendar  get  Calendar  DST OFFSET   but no way to get the   actual time zone offset being used  You must get these two separately   and add them together       GregorianCalendar set  year  month  day  hour  minute  does not set   the seconds to 0       DateFormat and GregorianCalendar do not mesh properly  You must   specify the Calendar twice  once indirectly as a Date       If the user has not configured his time zone correctly it will default   quietly to either PST or GMT       In GregorianCalendar  Months are numbered starting at January 0    rather than 1 as everyone else on the planet does  Yet days start at 1   as do days of the week with Sunday 1  Monday 2     Saturday 7  Yet   DateFormat  parse behaves in the traditional way with January 1

User · Answer

Personally  I took the strangeness of the Java calendar API as an indication that I needed to divorce myself from the Gregorian-centric mindset and try to program more agnostically in that respect   Specifically  I learned once again to avoid hardcoded constants for things like months   Which of the following is more likely to be correct   if  date getMonth      3  out print  March     if  date getMonth      Calendar MARCH  out print  March      This illustrates one thing that irks me a little about Joda Time - it may encourage programmers to think in terms of hardcoded constants    Only a little  though   It s not as if Joda is forcing programmers to program badly

User · Answer

Because language writing is harder than it looks  and handling time in particular is a lot harder than most people think  For a small part of the problem  in reality  not Java   see the YouTube video  The Problem with Time  amp  Timezones - Computerphile  at https   www youtube com watch v -5wpm-gesOY  Don t be surprised if your head falls off from laughing in confusion

User · Answer

Probably because C s  struct tm  does the same

User · Answer

In addition to DannySmurf s answer of laziness  I ll add that it s to encourage you to use the constants  such as Calendar JANUARY

User · Answer

I d say laziness  Arrays start at 0  everyone knows that   the months of the year are an array  which leads me to believe that some engineer at Sun just didn t bother to put this one little nicety into the Java code

User · Answer

Probably because C s  struct tm  does the same

User · Answer

It isn t exactly defined as zero per se  it s defined as Calendar January  It is the problem of using ints as constants instead of enums  Calendar January    0

User · Answer

tl dr  Month FEBRUARY getValue       February   2       2   Details  The Answer by Jon Skeet is correct   Now we have a modern replacement for those troublesome old legacy date-time classes  the java time classes   java time Month  Among those classes is the Month enum  An enum carries one or more predefined objects  objects that are automatically instantiated when the class loads  On Month we have a dozen such objects  each given a name  JANUARY  FEBRUARY  MARCH  and so on  Each of those is a static final public class constant  You can use and pass these objects anywhere in your code  Example  someMethod  Month AUGUST    Fortunately  they have sane numbering  1-12 where 1 is January and 12 is December   Get a Month object for a particular month number  1-12    Month month   Month of  2        2   February    Going the other direction  ask a Month object for its month number   int monthNumber   Month FEBRUARY getValue        February   2    Many other handy methods on this class  such as knowing the number of days in each month  The class can even generate a localized name of the month   You can get the localized name of the month  in various lengths or abbreviations   String output        Month FEBRUARY getDisplayName           TextStyle FULL            Locale CANADA FRENCH              f  vrier   Also  you should pass objects of this enum around your code base rather than mere integer numbers  Doing so provides type-safety  ensures a valid range of values  and makes your code more self-documenting  See Oracle Tutorial if unfamiliar with the surprisingly powerful enum facility in Java   You also may find useful the Year and YearMonth classes     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  java text 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

User · Answer

I d say laziness  Arrays start at 0  everyone knows that   the months of the year are an array  which leads me to believe that some engineer at Sun just didn t bother to put this one little nicety into the Java code

User · Answer

Personally  I took the strangeness of the Java calendar API as an indication that I needed to divorce myself from the Gregorian-centric mindset and try to program more agnostically in that respect   Specifically  I learned once again to avoid hardcoded constants for things like months   Which of the following is more likely to be correct   if  date getMonth      3  out print  March     if  date getMonth      Calendar MARCH  out print  March      This illustrates one thing that irks me a little about Joda Time - it may encourage programmers to think in terms of hardcoded constants    Only a little  though   It s not as if Joda is forcing programmers to program badly

User · Answer

Because doing math with months is much easier   1 month after December is January  but to figure this out normally you would have to take the month number and do math  12   1   13    What month is 13    I know  I can fix this quickly by using a modulus of 12    12   1    12   1   This works just fine for 11 months until November      11   1    12   0    What month is 0    You can make all of this work again by subtracting 1 before you add the month  then do your modulus and finally add 1 back again    aka work around an underlying problem     11 - 1   1    12    1   12    Lots of magical numbers    Now let s think about the problem with months 0 - 11    0   1    12   1    February  1   1    12   2    March  2   1    12   3    April  3   1    12   4    May  4   1    12   5    June  5   1    12   6    July  6   1    12   7    August  7   1    12   8    September  8   1    12   9    October  9   1    12   10    November  10   1    12   11    December  11   1    12   0    January   All of the months work the same and a work around isn t necessary

User · Answer

C based languages copy C to some degree  The tm structure  defined in time h  has an integer field tm mon with the  commented  range of 0-11   C based languages start arrays at index 0  So this was convenient for outputting a string in an array of month names  with tm mon as the index

[java] Why is January month 0 in Java Calendar?

Examples related to java

Examples related to calendar