Java Utililty Methods Day of Week

Calendar cal = Calendar.getInstance();
cal.setTime(d);
if (cal.getFirstDayOfWeek() == Calendar.MONDAY) {
    cal.add(Calendar.WEEK_OF_YEAR, -1);
cal.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
cal.set(Calendar.HOUR_OF_DAY, 23);
cal.set(Calendar.MINUTE, 59);
...

Calendar calendar = Calendar.getInstance(Locale.CHINA);
calendar.setTimeInMillis(date.getTime());
calendar.set(Calendar.DAY_OF_WEEK, 7);
calendar.set(Calendar.HOUR_OF_DAY, HOURS_OF_DAY);
calendar.set(Calendar.MINUTE, 59);
calendar.set(Calendar.SECOND, 59);
return new Date(calendar.getTimeInMillis());

Calendar c = new GregorianCalendar();
c.setFirstDayOfWeek(Calendar.SUNDAY);
c.setTime(date);
c.set(Calendar.DAY_OF_WEEK, c.getFirstDayOfWeek() + 6); 
return c.getTime();

Calendar calendar = Calendar.getInstance();
calendar.setFirstDayOfWeek(Calendar.SUNDAY);
calendar.setTime(date);
calendar.set(Calendar.DAY_OF_WEEK, calendar.getFirstDayOfWeek() + 6); 
return calendar.getTime();

Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
if (calendar.get(Calendar.DAY_OF_WEEK) == Calendar.SUNDAY) {
    calendar.add(Calendar.DAY_OF_YEAR, -1);
calendar.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
calendar.set(Calendar.HOUR_OF_DAY, 23);
calendar.set(Calendar.MINUTE, 59);
...

Calendar c = new GregorianCalendar();
c.setFirstDayOfWeek(Calendar.MONDAY);
c.setTime(date);
c.set(Calendar.DAY_OF_WEEK, c.getFirstDayOfWeek() + 6); 
return c.getTime();

Calendar c = new GregorianCalendar();
c.setFirstDayOfWeek(Calendar.MONDAY);
c.setTime(date);
c.set(Calendar.DAY_OF_WEEK, c.getFirstDayOfWeek() + 6);
return c.getTime();

String conStr = null;
int dayOfWeek = 0;
if (week == 0) {
    conStr = str;
    dayOfWeek = getCalendar(conStr).get(Calendar.DAY_OF_WEEK);
} else {
    conStr = addDays(str, week * 7);
    dayOfWeek = getCalendar(conStr).get(Calendar.DAY_OF_WEEK);
...

int minuscnt = whichDay(s);
minuscnt = minuscnt == 1 ? 0 : 7 - minuscnt + 1;
return addDays(s, minuscnt);

Date thismonday = getMondayOfWeek(date);
Calendar monday = getCalendar();
monday.setTime(thismonday);
monday.add(Calendar.DAY_OF_YEAR, -7);
return monday.getTime();