What's the difference between adding DAY_OF_MONTH or DAY_OF_YEAR to a Calendar object?

Solution 1:

For adding it really makes no difference, but this

Calendar c = Calendar.getInstance();
System.out.println(c.get(Calendar.DAY_OF_MONTH));
System.out.println(c.get(Calendar.DAY_OF_YEAR));

prints

28
363

Solution 2:

Calendar.add Adds or subtracts the specified amount of time to the given calendar field, based on the calendar's rules.

Here you have a list of the fields of Calendar that you can add or subtract:

• MILLISECOND is the number of milliseconds between 0 and 999

• SECOND is the number of seconds between 0 and 59

• MINUTE is the number of minutes between 0 and 59

• HOUR is the number of hours between 0 and 11

• HOUR_OF_DAY is the number of hours between 0 and 23

• DAY_OF_WEEK is the day in relation of the week between 1 and 7

• DAY_OF_MONTH is the day in relation of the month between 1 and 31

• DAY_OF_YEAR is the day in relation of the year between 1 and 366

• WEEK_OF_MONTH is the week in relation of the month starting from 1

• WEEK_OF_YEAR is the week in relation of the year starting from 1

• MONTH is the month in relation of the year between 0 and 11

• YEAR is the number of years starting from 1

Hours, days and weeks have multiple fields but it doesn't matter which one you choose¹. For example using -8 for DAY_OF_WEEK will work.

calendar.add(Calendar.DAY_OF_MONTH, -2); // subtract 2 days
calendar.add(Calendar.DAY_OF_WEEK, -2);  // subtract 2 days
calendar.add(Calendar.DAY_OF_YEAR, -2);  // subtract 2 days

calendar.add(Calendar.YEAR, -2);         // subtract 2 years

¹_{It doesn't matter only using Calendar.add, with other operations the results might be different.}

Solution 3:

Use Calendar.DATE for your purposes. In your case these three constants are synonyms.