Why is one of the approach works on setting date, and another isn't?

Question

In both cases, the date what I want to set in this example in millis is 1395227280627, and in human readable format is 3/19/2014 12:08:00 PM

1) Here is the first approach, which does not work correctly:

Calendar ret1=GregorianCalendar.getInstance();
ret1.set(Calendar.YEAR, year);
ret1.set(Calendar.MONTH, month);
ret1.set(Calendar.DAY_OF_YEAR, day);
ret1.set(Calendar.HOUR_OF_DAY, hour);
ret1.set(Calendar.MINUTE, minute);
ret1.set(Calendar.SECOND, 0);
Log.e("Time in millis:", Long.toString(ret1.getTimeInMillis()));

The output of this approach is 1390129680626 in millis and in human readable format is 1/19/2014 12:08:00 PM. The issue is, the month is not getting correctly set.

2) The second approach, which correctly works is:

Calendar ret2=GregorianCalendar.getInstance();
ret2.set(year, month, day, hour, minute, 0);
Log.e("Time in millis:", Long.toString(ret2.getTimeInMillis()));

The output of this approach is 1395227280627 in millis, and 3/19/2014 12:08:00 PM in human readable format, so exactly what I want. I was curious on what gone wrong, and after some research, loads of ppl stated that the java calendar is horrible, and has a lot of very weird thing, including some broken parts. I have started to backtrack the approach that works, here is the result:

Backtracking calendar.set(year, month, day, hour, minute, second)

/**
 * Sets the year, month, day of the month, hour of day, minute, and second fields.
 * Other fields are not changed; call {@link #clear} first if this is not desired.
 * The month value is 0-based, so it may be clearer to use a constant like {@code JANUARY}.
 */
public final void set(int year, int month, int day, int hourOfDay, int minute, int second) {
    set(year, month, day, hourOfDay, minute);
    set(SECOND, second);
}

So the second part translates to exactly what I did in the first approach, check.

Backtracking calendar.set(year, month, day, hourOfDay, minute)

/**
 * Sets the year, month, day of the month, hour of day, and minute fields.
 * Other fields are not changed; call {@link #clear} first if this is not desired.
 * The month value is 0-based, so it may be clearer to use a constant like {@code JANUARY}.
 */
public final void set(int year, int month, int day, int hourOfDay, int minute) {
    set(year, month, day);
    set(HOUR_OF_DAY, hourOfDay);
    set(MINUTE, minute);
}

So the hourOfDay and minute part translates to exactly what I did in the first approach, check.

Backtracking calendar.set(year, month, day)

/**
 * Sets the year, month, and day of the month fields.
 * Other fields are not changed; call {@link #clear} first if this is not desired.
 * The month value is 0-based, so it may be clearer to use a constant like {@code JANUARY}.
 */
public final void set(int year, int month, int day) {
    set(YEAR, year);
    set(MONTH, month);
    set(DATE, day);
}

So the year, month and day part exactly translates to what I did in the first approach.

The conclusion is, every call I make in the first approach gets called in the second approach in exactly the same way, so I don't understand, what is happenning. Can anyone help me out here, and explain why is this happenning?

Answer 1

I think the issue is that you are using the wrong calendar setting for setting the day

ret1.set(Calendar.DAY_OF_YEAR, day);

Which corresponds to a number between 1-365 (i.e. setting to 19 would effective set month to january 19)

i think you want

ret1.set(Calendar.DAY_OF_MONTH, day);