Getting proper day of the week and month

Question

I have an assignment for my classes:

The class should have a methods of calculating the number of days between two dates, returns the day of the week and giving the sign of the zodiac for a given date.

And here is the code I've written:

import java.util.GregorianCalendar;

public class Data {
    private GregorianCalendar date;

    public Data(int year, int month, int day) {
        date = new GregorianCalendar(year, month + 1, day);
    }

    public int differenceInDaysFrom(int year, int month, int day) {
        GregorianCalendar tempDate = new GregorianCalendar(year, month, day);
        int daysBetween = (int)(tempDate.getTimeInMillis()-date.getTimeInMillis())/(1000 * 60 * 60 * 24);
        return Math.abs(daysBetween);
    }

    public String dayOfTheWeek() {
        String[] stringDays = new String[]{ "Monday",
                                            "Tuesday",
                                            "Wednesday",
                                            "Thursday",
                                            "Friday",
                                            "Saturday",
                                            "Sunday" };
        return stringDays[date.get(GregorianCalendar.DAY_OF_WEEK) - 1];
    }

    public void zodiacSign() {
        int day = date.get(GregorianCalendar.DATE);
        int month = date.get(GregorianCalendar.MONTH);

        System.out.println(day + " " + month);
    }
}

1. When I initialize date with YYY\MM\DD everything works perfect when checking dayOfTheWeek for the near-future dates but when I put my birth date (1991\11\14) it returns Wednesday but I was born on Thursday.

2. When I'm trying to get day and mont for checking the zodiac sign it totally freak out and returns 0 when I enter 11 (for month, days works good).

3. What is more... When I started wangling with +1 to month even differenceInDaysFrom stopped working properly

Answer 1

for the problem of your birthday (wed or Thursday):

first you have to pass month 10 as Nov. since 0=January. this has been spotted out by other answers.

then you need to declare your String array as:

    new String[] { "Sunday", "Monday", "Tuesday", 
"Wednesday", "Thursday", "Friday", "Saturday" };

because, DAY_OF_WEEK, 1=Sunday, 2=MONDAY, check javaDoc of Calendar class. Then you should get "Thursday"

for the zodiac method. you entered 11, so your date object received month parameter is 11+1=12. 12 is not valid month (0-11 are valid, as mentioned above, Jan=0) Therefore you got freak out. :)

Answer 2

Check this out:

Days d = Days.daysBetween(startDate, endDate);
int days = d.getDays();
http://joda-time.sourceforge.net/faq.html#datediff

One of your problems is that you +1 on month, and months go from 0 - 11 (Stupid I know) so 11+1 is 12 which is not valid. (I think there is a strictness you can set)

Answer 3

Instead of month + 1 you need month-1, also wrap 11 -> 0.

date = new GregorianCalendar(year, (month == 0) ? 11 : month - 1, day);