Unable to set GregorianCalendar Month and Date

问题

Im trying to set the month and date of a Gregorian Calendar:

GregorianCalendar startCalendar = new GregorianCalendar();

startCalendar.set(GregorianCalendar.MONTH, 3);
System.out.println(startCalendar.MONTH);
startCalendar.set(GregorianCalendar.DATE, 9);
System.out.println(startCalendar.DATE);

The output is:

2
5

It doesn't seem to matter which numbers i use (ie. if i replace the 3 and 9), it always has the same output

回答1:

References:

GregorianCalendar (Java Platform SE 8 )
Calendar (Java Platform SE 8 )

MONTH and DATE are field numbers and aren't the actual value of the fields. You should use get() method to get the number set.

GregorianCalendar startCalendar = new GregorianCalendar();

startCalendar.set(GregorianCalendar.MONTH, 3);
System.out.println(startCalendar.get(GregorianCalendar.MONTH));
startCalendar.set(GregorianCalendar.DATE, 9);
System.out.println(startCalendar.get(GregorianCalendar.DATE));

回答2:

startCalendar.MONTH is the same as Calendar.MONTH, and is a static field declared in the Calendar class as:

public final static int MONTH = 2;

To get the month from the calendar, you need to call get():

startCalendar.get(Calendar.MONTH)

Note that you should always qualify static fields by the actual class declaring them (e.g. Calendar.MONTH), never by a reference variable (e.g. startCalendar.MONTH) and never by subclass (e.g. GregorianCalendar.MONTH).

So, your code should be:

GregorianCalendar startCalendar = new GregorianCalendar();

startCalendar.set(Calendar.MONTH, 3);
System.out.println(startCalendar.get(Calendar.MONTH));
startCalendar.set(Calendar.DATE, 9);
System.out.println(startCalendar.get(Calendar.DATE));

来源：https://stackoverflow.com/questions/36110408/unable-to-set-gregoriancalendar-month-and-date

标签

java

calendar

gregorian-calendar