adding days to a date

date, gregorian-calendar, java

Solution

The `Calendar` object has an `add` method which allows one to add or subtract values of a specified field.

For example,

Calendar c = new GregorianCalendar(2009, Calendar.JANUARY, 1);
c.add(Calendar.DAY_OF_MONTH, 1);

The constants for specifying the field can be found in the "Field Summary" of the `Calendar` class.

Just for future reference, The Java API Specification contains a lot of helpful information about how to use the classes which are part of the Java API.

Update:

I am getting the error found void but expected int, in 'newDay = startDate.add(5, 1);' What should I do?

The `add` method does not return anything, therefore, trying to assign the result of calling `Calendar.add` is not valid.

The compiler error indicates that one is trying to assign a `void` to a variable with the type of `int`. This is not valid, as one cannot assign "nothing" to an `int` variable.

Just a guess, but perhaps this may be what is trying to be achieved:

// Get a calendar which is set to a specified date.
Calendar calendar = new GregorianCalendar(2009, Calendar.JANUARY, 1);

// Get the current date representation of the calendar.
Date startDate = calendar.getTime();

// Increment the calendar's date by 1 day.
calendar.add(Calendar.DAY_OF_MONTH, 1);

// Get the current date representation of the calendar.
Date endDate = calendar.getTime();

System.out.println(startDate);
System.out.println(endDate);

Output:

Thu Jan 01 00:00:00 PST 2009
Fri Jan 02 00:00:00 PST 2009

What needs to be considered is what `Calendar` actually is.

A `Calendar` is not a representation of a date. It is a representation of a calendar, and where it is currently pointing at. In order to get a representation of where the calendar is pointing at at the moment, one should obtain a `Date` from the `Calendar` using the `getTime` method.

Problem

Original source