Date object to Calendar Java

Question

I have a class Movie in it i have a start Date  a duration and a stop Date  Start and stop Date are Date Objects  private Date startDate       It s an assignment so i cant change that  now I want to automatically calculate the stopDate by adding the duration  in min  to the startDate   By my knowledge working with the time manipulating functions of Date is deprecated hence bad practice but on the other side i see no way to convert the Date object to a calendar object in order to manipulate the time and reconvert it to a Date object  Is there a way  And if there is what would be best practice

User · Answer

something like  movie setStopDate movie getStartDate     movie getDurationInMinutes    60000

User · Answer

You don t need to convert to Calendar for this  you can just use getTime   setTime   instead      getTime      Returns the number of milliseconds since January 1  1970  00 00 00 GMT represented by this Date object        setTime long time    Sets this Date object to represent a point in time that is time milliseconds after January 1  1970 00 00 00 GMT      There are 1000 milliseconds in a second  and 60 seconds in a minute  Just do the math       Date now   new Date        Date oneMinuteInFuture   new Date now getTime     1000L   60       System out println now       System out println oneMinuteInFuture     The L suffix in 1000 signifies that it s a long literal  these calculations usually overflows int easily

User · Answer

Calendar setTime    It s often useful to look at the signature and description of API methods  not just their name    - Even in the Java standard API  names can sometimes be misleading

User · Answer

Calendar tCalendar   Calendar getInstance    tCalendar setTime date     date is a java util Date object  You may use Calendar getInstance   as well to obtain the Calendar instance much more efficient

User · Answer

tl dr  Instant stop        myUtilDateStart toInstant                       plus  Duration ofMinutes  x          java time  Other Answers are correct  especially the Answer by Borgwardt  But those Answers use outmoded legacy classes    The original date-time classes bundled with Java have been supplanted with java time classes  Perform your business logic in java time types  Convert to the old types only where needed to work with old code not yet updated to handle java time types   If your Calendar is actually a GregorianCalendar you can convert to a ZonedDateTime  Find new methods added to the old classes to facilitate conversion to from java time types   if  myUtilCalendar instanceof GregorianCalendar         GregorianCalendar gregCal    GregorianCalendar  myUtilCalendar     Downcasting from the interface to the concrete class      ZonedDateTime zdt   gregCal toZonedDateTime        Create  ZonedDateTime  with same time zone info found in the  GregorianCalendar  end if    If your Calendar is not a Gregorian  call toInstant to get an Instant object  The Instant class represents a moment on the timeline in UTC with a resolution of nanoseconds   Instant instant   myCal toInstant      Similarly  if starting with a java util Date object  convert to an Instant  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   myUtilDate toInstant      Apply a time zone to get a ZonedDateTime   ZoneId z   ZoneId of   America Montreal     ZonedDateTime zdt   instant atZone  z      To get a java util Date object  go through the Instant   java util Date utilDate   java util Date from  zdt toInstant        For more discussion of converting between the legacy date-time types and java time  and a nifty diagram  see my Answer to another Question   Duration  Represent the span of time as a Duration object  Your input for the duration is a number of minutes as mentioned in the Question   Duration d   Duration ofMinutes  yourMinutesGoHere      You can add that to the start to determine the stop   Instant stop   startInstant plus  d         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

User · Answer

Here is a full example on how to transform your date in different types   Date date   Calendar getInstance   getTime            Display a date in day  month  year format     DateFormat formatter   new SimpleDateFormat  dd MM yyyy        String today   formatter format date       System out println  Today       today           Display date with day name in a short format     formatter   new SimpleDateFormat  EEE  dd MM yyyy        today   formatter format date       System out println  Today       today           Display date with a short day and month name     formatter   new SimpleDateFormat  EEE  dd MMM yyyy        today   formatter format date       System out println  Today       today           Formatting date with full day and month name and show time up to        milliseconds with AM PM     formatter   new SimpleDateFormat  EEEE  dd MMMM yyyy  hh mm ss SSS a        today   formatter format date       System out println  Today       today

User · Answer

What you could do is creating an instance of a GregorianCalendar and then set the Date as a start time   Date date  Calendar myCal   new GregorianCalendar    myCal setTime date     However  another approach is to not use Date at all  You could use an approach like this   private Calendar startTime  private long duration  private long startNanos      Nano-second precision  could be less precise     this startTime   Calendar getInstance    this duration   0  this startNanos   System nanoTime     public void setEndTime             this duration   System nanoTime   - this startNanos     public Calendar getStartTime             return this startTime     public long getDuration             return this duration      In this way you can access both the start time and get the duration from start to stop  The precision is up to you of course

[java] Date object to Calendar [Java]

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