How to subtract X days from a date using Java cale

问题:

Anyone know a simple way using Java calendar to subtract X days from a date?

I have not been able to find any function which allows me to directly subtract X days from a date in Java. Can someone point me to the right direction?

回答1:

Taken from the docs here:

Adds or subtracts the specified amount of time to the given calendar field, based on the calendar\'s rules. For example, to subtract 5 days from the current time of the calendar, you can achieve it by calling:

Calendar calendar = Calendar.getInstance(); // this would default to now
calendar.add(Calendar.DAY_OF_MONTH, -5).

回答2:

You could use the add method and pass it a negative number. However, you could also write a simpler method that doesn\'t use the Calendar class such as the following

public static void addDays(Date d, int days)
{
    d.setTime( d.getTime() + (long)days*1000*60*60*24 );
}

This gets the timestamp value of the date (milliseconds since the epoch) and adds the proper number of milliseconds. You could pass a negative integer for the days parameter to do subtraction. This would be simpler than the \"proper\" calendar solution:

public static void addDays(Date d, int days)
{
    Calendar c = Calendar.getInstance();
    c.setTime(d);
    c.add(Calendar.DATE, days);
    d.setTime( c.getTime().getTime() );
}

Note that both of these solutions change the Date object passed as a parameter rather than returning a completely new Date. Either function could be easily changed to do it the other way if desired.

回答3:

Anson\'s answer will work fine for the simple case, but if you\'re going to do any more complex date calculations I\'d recommend checking out Joda Time. It will make your life much easier.

FYI in Joda Time you could do

DateTime dt = new DateTime();
DateTime fiveDaysEarlier = dt.minusDays(5);

回答4:

tl;dr

LocalDate.now().minusDays( 10 )

Better to specify time zone.

LocalDate.now( ZoneId.of( \"America/Montreal\" ) ).minusDays( 10 )

Details

The old date-time classes bundled with early versions of Java, such as java.util.Date/.Calendar, have proven to be troublesome, confusing, and flawed. Avoid them.

java.time

Java 8 and later supplants those old classes with the new java.time framework. See Tutorial. Defined by JSR 310, inspired by Joda-Time, and extended by theThreeTen-Extra project. The ThreeTen-Backport project back-ports the classes to Java 6 & 7; the ThreeTenABP project to Android.

The Question is vague, not clear if it asks for a date-only or a date-time.

LocalDate

For a date-only, without time-of-day, use the LocalDate class. Note that a time zone in crucial in determining a date such as \"today\".

LocalDate today = LocalDate.now( ZoneId.of( \"America/Montreal\" ) );
LocalDate tenDaysAgo = today.minusDays( 10 );

ZonedDateTime

If you meant a date-time, then use the Instant class to get a moment on the timeline in UTC. From there, adjust to a time zone to get a ZonedDateTime object.

Instant now = Instant.now();  // UTC.
ZoneId zoneId = ZoneId.of( \"America/Montreal\" );
ZonedDateTime zdt = ZonedDateTime.ofInstant( instant , zoneId );
ZonedDateTime tenDaysAgo = zdt.minusDays( 10 );

---

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, & SimpleDateFormat.

The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.

To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.

You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes.

Where to obtain the java.time classes?

• Java SE 8, Java SE 9, Java SE 10, 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 Java SE 7
  • Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
• Android
  • Later versions of Android bundle implementations of the java.time classes.
  • For earlier Android (<26), the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP….

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.

回答5:

int x = -1;
Calendar cal = ...;
cal.add(Calendar.DATE, x);

edit: the parser doesn\'t seem to like the link to the Javadoc, so here it is in plaintext:

http://java.sun.com/j2se/1.4.2/docs/api/java/util/Calendar.html#add(int, int)

回答6:

Instead of writing my own addDays as suggested by Eli, I would prefer to use DateUtils from Apache. It is handy especially when you have to use it multiple places in your project.

The API says:

addDays(Date date, int amount)

Adds a number of days to a date returning a new object.

Note that it returns a new Date object and does not make changes to the previous one itself.

回答7:

Someone recommended Joda Time so - I have been using this CalendarDate class http://calendardate.sourceforge.net

It\'s a somewhat competing project to Joda Time, but much more basic at only 2 classes. It\'s very handy and worked great for what I needed since I didn\'t want to use a package bigger than my project. Unlike the Java counterparts, its smallest unit is the day so it is really a date (not having it down to milliseconds or something). Once you create the date, all you do to subtract is something like myDay.addDays(-5) to go back 5 days. You can use it to find the day of the week and things like that. Another example:

CalendarDate someDay = new CalendarDate(2011, 10, 27);
CalendarDate someLaterDay = today.addDays(77);

And:

//print 4 previous days of the week and today
String dayLabel = \"\";
CalendarDate today = new CalendarDate(TimeZone.getDefault());
CalendarDateFormat cdf = new CalendarDateFormat(\"EEE\");//day of the week like \"Mon\"
CalendarDate currDay = today.addDays(-4);
while(!currDay.isAfter(today)) {
    dayLabel = cdf.format(currDay);
    if (currDay.equals(today))
        dayLabel = \"Today\";//print \"Today\" instead of the weekday name
    System.out.println(dayLabel);
    currDay = currDay.addDays(1);//go to next day
}

回答8:

It can be done easily by the following

Calendar calendar = Calendar.getInstance();
        // from current time
        long curTimeInMills = new Date().getTime();
        long timeInMills = curTimeInMills - 5 * (24*60*60*1000);    // `enter code here`subtract like 5 days
        calendar.setTimeInMillis(timeInMills);
        System.out.println(calendar.getTime());

        // from specific time like (08 05 2015)
        calendar.set(Calendar.DAY_OF_MONTH, 8);
        calendar.set(Calendar.MONTH, (5-1));
        calendar.set(Calendar.YEAR, 2015);
        timeInMills = calendar.getTimeInMillis() - 5 * (24*60*60*1000);
        calendar.setTimeInMillis(timeInMills);
        System.out.println(calendar.getTime());

回答9:

Eli Courtwright second solution is wrong, it should be:

Calendar c = Calendar.getInstance();
c.setTime(date);
c.add(Calendar.DATE, -days);
date.setTime(c.getTime().getTime());