如何使用基本的Java计算两个日期之间的差异

Question

我刚开始上大学，基本上就开始使用Java，我想知道如何制作一个代码来计算两个日期之间的天数，但不使用花费毫秒的程序以及我在其他答案中已经看到的东西。这是我创建的代码，但无法正常运行，大多数情况下会错过一天或类似的时间。请我真的需要您的帮助

Answer 1

Use a SimpleCalendar or GregorianCalendar classes...

but basing on what you posted, I'm unsure how to best suggest using those two... i'll draft a simple example shortly.

After some thought I'll just leave this here Difference in days between two dates in Java?

Answer 2

Taken from: http://www.staff.science.uu.nl/~gent0113/calendar/isocalendar_text5.htm

An approach could be to calculate the number of days from a fixed time for both dates and then just subtract those days. This will give you the difference of days between date 1 and date 2

The following method returns the number of days passed since 0 January 0 CE

public int calculateDate( int day, int month, int year) {
  if (month < 3) {
      year--;
      month = month + 12;
  } 
  return 365 * year + year/4 - year/100 + year/400 + ((month+1) * 306)/10 + (day - 62); 
}

In you code now you should calculate the number of days since 0BC for both dates and then subtract them:

public void run() {
 ....

 int dayDifference = calculateDate(day1, month1, year1) - calculateDate(day2, month2, year2);

....
}

Answer 3

tl;dr

java.time.temporal.ChronoUnit.DAYS.between(
    LocalDate.of( 2012 , Month.MARCH , 23 ) ,
    LocalDate.of( 2012 , Month.MAY , 17 ) 
)

55

java.time

The modern approach uses java.time classes that supplant the troublesome old legacy date-time classes.

LocalDate

The LocalDate class represents a date-only value without time-of-day and without time zone.

A time zone is crucial in determining a date. For any given moment, the date varies around the globe by zone. For example, a few minutes after midnight in Paris France is a new day while still “yesterday” in Montréal Québec .

If no time zone is specified, the JVM implicitly applies its current default time zone. That default may change at any moment, so your results may vary. Better to specify your desired/expected time zone explicitly as an argument.

Specify a proper time zone name in the format of continent/region , such as America/Montreal , Africa/Casablanca , or Pacific/Auckland . Never use the 3-4 letter abbreviation such as EST or IST as they are not true time zones, not standardized, and not even unique(!).

ZoneId z = ZoneId.of( "America/Montreal" ) ;  
LocalDate today = LocalDate.now( z ) ;

If you want to use the JVM's current default time zone, ask for it and pass as an argument. If omitted, the JVM's current default is applied implicitly. Better to be explicit, as the default may be changed at any moment during runtime by any code in any thread of any app within the JVM.

ZoneId z = ZoneId.systemDefault() ;  // Get JVM’s current default time zone.

Or specify a date. You may set the month by a number, with sane numbering 1-12 for January-December.

LocalDate ld = LocalDate.of( 1986 , 2 , 23 ) ;  // Years use sane direct numbering (1986 means year 1986). Months use sane numbering, 1-12 for January-December.

Or, better, use the Month enum objects pre-defined, one for each month of the year. Tip: Use these Month objects throughout your codebase rather than a mere integer number to make your code more self-documenting, ensure valid values, and provide type-safety .

LocalDate ld = LocalDate.of( 1986 , Month.FEBRUARY , 23 ) ;

ChronoUnit.DAYS

To get a count of days between two dates, call on the ChronoUnit enum object DAYS .

long days = ChronoUnit.DAYS.between( earlierLocalDate , laterLocalDate ) ;

---

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 .

Where to obtain the java.time classes?

• Java SE 8 , Java 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 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, 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 .