Is this a date in Feburary or in March? cal.set(2010, 1, 10)

Question

I have set this calendar in my app:

Calendar cal = Calendar.getInstance();
cal.set(2010, 1, 10); 

I'm using this SimpleDateFormat to get the month as a word:

SimpleDateFormat formatMonth = new SimpleDateFormat("MM");

In one class it comes out as February 10th, 2010.

In another it comes out as March 10th, 2010.

Which is correct?

Answer 1

The month argument to Calendar.set() is zero-based, so 1 means February. The first behavior is the correct one.

I suspect something in your other class is mistakenly trying to compensate for zero-based month indexes, and that results in an off-by-one error.

Answer 2

Given all the hassles associated with the JDK date handling, you should really be looking to use Joda time instead. The above code would be rewritten as

DateTime dt = new DateTime().withDate(2010,2,10).withTime(12,13,14,0);

and represents 10 February 2010 at 12:13:14.000 in UTC. No ambiguity, thread safe and immutable.

You should note that SimpleDateFormat is not thread safe.

Answer 3

The calendar class has constants for months

 Calendar.JANUARY

for example. You should be using those.