Java Utililty Methods Date to Day

long time = date.getTime();
return new Date(time - ((time + timezoneOffset) % 86400000L));

long currDateMills = date.getTime();
long extraMills = day * 3600 * 1000 * 24;
Calendar result = Calendar.getInstance();
result.setTimeInMillis(currDateMills + extraMills);
return result.getTime();

if (dateParam == null) {
    throw new IllegalArgumentException("The dateParam  must not be null");
Calendar cal = Calendar.getInstance();
cal.setTimeInMillis(dateParam.getTime());
return cal.get(Calendar.DAY_OF_WEEK);

java.util.Calendar c = java.util.Calendar.getInstance();
c.setTime(date);
return c.get(java.util.Calendar.DAY_OF_MONTH);

Calendar cal = parseDateTime(strDate);
return cal.get(Calendar.DATE);

Calendar start = Calendar.getInstance();
start.setTime(startDate);
start.set(Calendar.HOUR_OF_DAY, 0);
start.set(Calendar.MINUTE, 0);
start.set(Calendar.SECOND, 0);
start.set(Calendar.MILLISECOND, 0);
Calendar end = Calendar.getInstance();
end.setTime(endDate);
...

Calendar calendar = Calendar.getInstance();
calendar.setTime(_startDate);
int startDay = calendar.get(Calendar.DAY_OF_YEAR);
int startYear = calendar.get(Calendar.YEAR);
calendar.clear();
calendar.setTime(_endDate);
int endDay = calendar.get(Calendar.DAY_OF_YEAR);
int endYear = calendar.get(Calendar.YEAR);
...

Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
calendar.set(Calendar.HOUR_OF_DAY, 0);
calendar.set(Calendar.MINUTE, 0);
calendar.set(Calendar.SECOND, 0);
calendar.set(Calendar.MILLISECOND, 0);
calendar.add(Calendar.DAY_OF_MONTH, 1);
calendar.add(Calendar.MILLISECOND, -1);
...

Calendar end = new GregorianCalendar();
end.setTime(date);
end.set(Calendar.HOUR_OF_DAY, 23);
end.set(Calendar.MINUTE, 59);
end.set(Calendar.SECOND, 59);
return end.getTime();

Calendar cal = Calendar.getInstance();
cal.setTime(date);
cal.set(Calendar.HOUR_OF_DAY, 23);
cal.set(Calendar.MINUTE, 59);
cal.set(Calendar.SECOND, 59);
cal.set(Calendar.MILLISECOND, 999);
return cal;