Date handle functions in Java

I showed a small function about how to get a day of week based on the inputted date in my previous article. But there are still some more functions related to Date that i usually have to deal with, so i also want to share them here

1. Plus a date and a year

public static Date addYear(Date date, int value) {
        GregorianCalendar calendar = new GregorianCalendar();
        calendar.setTime(date);
        calendar.add(Calendar.YEAR, value);

        return calendar.getTime();
}

2. Plus a date and a month

public static Date addMonth(Date date, int value) {
        GregorianCalendar calendar = new GregorianCalendar();
        calendar.setTime(date);
        calendar.add(Calendar.MONTH, value);

        return calendar.getTime();
}

3. Plus a date and a day

public static Date addDay(Date date, int value) {
        GregorianCalendar calendar = new GregorianCalendar();
        calendar.setTime(date);
        calendar.add(Calendar.DAY_OF_MONTH, value);

        return calendar.getTime();
}

4. Plus a date and minute

public static Date addMinute(Date date, int value) {
        GregorianCalendar calendar = new GregorianCalendar();
        calendar.setTime(date);
        calendar.add(Calendar.MINUTE, value);

        return calendar.getTime();
}

5. Calculate years old

// bornDate is a date string based on [yyyyMMdd] format
public static String calAge(String bornDate) throws Exception {
        // If the input date is null
        if (bornDate == null || bornDate.length() == 0) {
            bornDate = "00000000";
        }

        Calendar cal = new GregorianCalendar(new Integer(bornDate.substring(0, 4)), 
                                             new Integer(bornDate.substring(4, 6)) - 1, 
                                             new Integer(bornDate.substring(6, 8)));
        
        Calendar now = new GregorianCalendar();
        
        int age = now.get(Calendar.YEAR) - cal.get(Calendar.YEAR);
        
        if(cal.get(Calendar.MONTH) > now.get(Calendar.MONTH)
          || (cal.get(Calendar.MONTH) == now.get(Calendar.MONTH)
          && cal.get(Calendar.DAY_OF_MONTH) > now.get(Calendar.DAY_OF_MONTH))) {
            age--;
        }

        return age + " years old";
}

6. Get first day of week

public static Date getFirstDayOfWeek(Date date) {
        GregorianCalendar calendar = new GregorianCalendar();
        calendar.setTime(date);
        calendar.set(
                Calendar.DAY_OF_WEEK,
                calendar.getActualMinimum(Calendar.DAY_OF_WEEK));

        return calendar.getTime();
}

7. Get day of week

 public static int getDayOfWeek(Date date) {
        GregorianCalendar calendar = new GregorianCalendar();
        calendar.setTime(date);

        return calendar.get(Calendar.DAY_OF_WEEK);
}

8. Get first day of month

public static Date getFirstDayOfMonth(Date date) {
        GregorianCalendar calendar = new GregorianCalendar();
        calendar.setTime(date);
        calendar.set(
                Calendar.DAY_OF_MONTH,
                calendar.getActualMinimum(Calendar.DAY_OF_MONTH));
        
        return calendar.getTime();
}

9. Get last day of month

public static Date getLastDayOfMonth(Date date) {
        GregorianCalendar calendar = new GregorianCalendar();
        calendar.setTime(date);
        calendar.set(
                Calendar.DAY_OF_MONTH,
                calendar.getActualMaximum(Calendar.DAY_OF_MONTH));
        
        return calendar.getTime();
}

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